CXM/DXM CXM/DXM Digital Heat Pump Controllers Application, Operation & Maintenance Instructions 97B0003N08 Revision: 01/10/05 Table of Contents CXM / DXM Control Features Comparison 2 Part I - CXM Control 3 CXM Overview 3 Physical Dimensions and Layout 3 Product Specification 3 Safety Features 5 Diagnostic Features 6 Unit Operation Description 6 Typical Schematic 7 Part II - DXM Control 8 DXM Overview 8 Physical Dimensions and Layout 8 Basic Control Features 9 Field Selectable Inputs 9 Safety Features 10 Diagnostic Features 12 Unit Operation Description 12 Special Application Notes 13 Communications 14 Typical Schematic 16 Part III - CXM/DXM Notes CXM/DXM Sensors 17 Thermostats 18 CXM and DXM Inputs and Outputs Reference 19 Troubleshooting Chart 20 Functional Troubleshooting 21 Performance Troubleshooting 22 Revisiom History 24
CXM / DXM Electronic Control Features Comparison Basic Features CXM CXM-Lon CXM-MPC DXM DXM-Lon DXM-MPC High and Low Refrigerant Pressure Protection S S S S S S Water Coil Freeze Protection S S S S S S True 24VA Thermostat Signals S S S S S S Thermostat Inputs Compatible with Triacs S S S S S S Condensate Overfl ow Sensor S S S S S S Anti-Short-Cyle Time Delay S S S S S S Random Start S S S S S S Alarm (selectable dry contact or 24VA) S S S S S S Water Valve Relay S S S S S S Water Valve Relay with Compressor Delay N/A N/A N/A S S S Emergency Shutdown N/A DDC DDC S DDC DDC Night Setback with Override N/A DDC DDC S DDC DDC Outdoor Air Damper Control N/A N/A N/A S S S Advanced Features Intelligent Reset S S S S S S High and Low Voltage Protection S S S S S S Air Coil Freeze Protection S S S S S S Freeze Setpoint Field Select (water, antifreeze) S S S S S S Electric Heat Control Outputs S S S S S S Boilerless Electric Heat Control N/A N/A N/A S S S Intelligent Reversing Valve Operation N/A DDC DDC S S S High/Low Fan Speed Outputs N/A N/A N/A S S S Intelligent Fan Speed Control N/A N/A N/A S S S Thermostat Type Select (Y,O or Y,W) N/A N/A N/A S N/A N/A Reversing Valve Signal Select (O or B) N/A N/A N/A S N/A N/A Dehumidistat Input N/A N/A N/A S S S Reheat Dehumidifi cation Control* N/A N/A N/A O O O Multiple Units on One Thermostat/Wall Sensor N/A DDC DDC S DDC DDC Service and Reliability Features Service Test Mode S S S S S S LED Fault and Status Lights S S S S S S Fault Memory after Reset S S S S S S Unit Performance Sentinel S S S S S S Harness-Type Factory Wiring Connections S S S S S S Fully Noise-Tested Design S S S S S S CE Approval S S S S S S Removable Low Voltage Connector N/A N/A N/A S S S DDC / Energy Management Features Echelon LonMark Compliant N/A S N/A N/A S N/A BACNET Compliant N/A N/A S N/A N/A S Johnson N2 Compliant N/A N/A S N/A N/A S Modbus Compliant N/A N/A S N/A N/A S Leaving Air and Water Temperature Sensor N/A S S N/A S S Digital Wall Sensor N/A O O N/A O O S = Standard O = Optional DDC = Feature can be provided by DDC System CXM-Lon = CXM with LonMark Module DXM-Lon = DXM with LonMark Module CXM-MPC = CXM with MPC Module DXM-MPC = DXM with MPC Module * = Check with your Factory Representative for model availability MPC = Multiple ProtoCol (BACNET, N2, Modbus) Page 2 CXM/DXM Electronic Heat Pump Control
CXM Overview The CXM control is a microprocessor based heat pump controller that is simple to use, yet provides all the necessary features to improve the operation and safety of water source heat pumps. CM Part Number: 17B0001N01 CXM Control Board General Operating Parameters The following are general operating parameters for the CXM control: Operating Environment: -40 F to 176 F and up to 95% relative humidity, non-condensing. Storage Environment: -40 F to 185 F and up to 95% relative humidity, non-condensing. Power Requirements: CXM only power draw - Normally 5 VA draw at 24VAC. Maximum 9 VA draw at 24VAC. A dedicated 24VAC, 50-60Hz, 1Ph, 40VA transformer minimum is required for typical wshp application. Relay Contact Ratings: The following relays are mounted on the CXM control. Compressor Relay: 40VA at 24VAC. Alarm Relay: 28VA at 24VAC. Part I - CXM Electronic Heat Pump Control PART I CXM ELECTRONIC HEAT PUMP CONTROL Grounding: The control board is grounded through two of the metal standoffs. Field connection ratings for the CXM Control: "A" terminal: 20VA at 24VAC. Product Specification Features Anti-short cycle protection High and Low pressure cutouts Water Coil freeze protection Air Coil freeze protection Random Start Unit Performance Sentinel Over/Under Voltage protection Diagnostic LED Reset Lockout at unit or disconnect Intelligent Reset Condensate Overflow sensor Test Mode Electric Heat Outputs Accessory Water Valve Connection CXM Physical Dimensions and Layout Factory 0.250 Quick Connects 4.00 Field Thermostat Connections 6.00 C R Y Y W O G R C AL1 AL2 A P1 BR BRG Test JW3 JW2 JW1- AL2 Dry CCG CC Off On FP1 Low Temp FP2 Low Temp Micro Comp Relay Status LED P2 1 HP HP LP LP FP1 FP1 FP2 FP2 RV RV CO 12 CO 1 4 P3 24Vdc EH1 EH2 5.50 Factory Low Voltage Molex connector for unit harness Factory Low Voltage Molex connector for electric heat harness 3/8 standoff Alarm Relay CO 17B0001N01 1.50 3.50 4 Mounting Screws: #6 sheet metal screw 1 long CXM Electronic Heat Pump Control Page 3
Part I - CXM Electronic Heat Pump Control Field Selectable Inputs Test Mode - Test Mode allows the service personnel to check the operation of the control in a timely manner. By momentarily shorting the test terminals, the CXM control enters a 20 minute Test Mode period in which all time delays are sped up 15 times. Upon entering Test Mode, the Status LED will fl ash a code representing the last fault. For Diagnostic ease at the thermostat, the alarm relay will also cycle during test mode. The Alarm relay will cycle on and off similar to the status LED to indicate a code representing the last fault, at the thermostat. Note: Code 1 indicates there is no fault in memory; stated differently, the control has not faulted since the last power-down to power-up sequence. Test mode can be exited by shorting the test terminals for 3 seconds. Test mode can also be entered and exited by cycling the G input, 3 times within a 60 second time period. During Test mode, the control monitors to see if the FP1 and FP2 thermistors are in the appropriate place. If the control is in Test mode, the control will lockout, with Code 9, after 30 seconds if: a) the compressor is On in cooling mode and the FP1 sensor is colder than the FP2 sensor. Or, b) the compressor is On in heating mode and the FP2 sensor is colder than the FP1 sensor. Retry Mode - If the control is attempting a retry of a fault, the status LED will slow fl ash (slow fl ash=one fl ash every 2 seconds) to indicate the control is in process of retrying. Note: In the following field configuration options, jumper wires should be clipped ONLY when power is removed from the CXM control. Water Coil Freeze Protection Limit Setting - Jumper 3 (JW3-FP1 Low Temp) provides field selection of temperature limit setting for FP1 to be 30 F or 10 F. Not Clipped=30 F. Clipped=10 F. Table 1: LED & Alarm Relay Operations Air Coil Freeze Protection Limit Setting - Jumper 2 (JW2- FP2 Low Temp) provides field selection of temperature limit setting for FP2 to be 30 F or 10 F. Not Clipped=30 F. Clipped=10 F. Alarm Relay Setting - Jumper 1 (JW1-AL2 Dry) provides field selection of Alarm Relay terminal AL2 to be jumpered to 24VAC or to be dry (no connection). Not Clipped=AL2 connected to R. Clipped=AL2 dry contacts (no connection). DIP Switches Note: In the following field configuration options, DIP switches should only be moved when power is removed from the CXM control, to insure proper operation. DIP Switch 1: Unit Performance Sentinel Disable - provides field selection to disable the UPS feature. On = Enabled. Off = Disabled. DIP Switch 2: Stage 2 Selection- provides selection of whether compressor has an on delay. If set to stage 2, the compressor will have a 3 second delay before energizing. Also, if set for stage 2, the alarm relay will NOT cycle during test mode. On = Stage 1. Off = Stage 2 DIP Switch 3: - Not Used. DIP Switch 4: DDC Output at EH2 - provides selection for DDC operation. If set to DDC Output at EH2, the EH2 terminal will continuously output the last fault code of the controller. If set to EH2 normal, then the EH2 will operate as standard electric heat output. On = EH2 Normal. Off = DDC Output at EH2. NOTE: Some CXM controls only have a 2 position DIP switch package. If this is the case, then this option can be selected by clipping the jumper which is in position 4 of SW1: Jumper not clipped = EH2 Normal. Jumper clipped = DDC Output at EH2. DIP Switch 5: Factory Setting - Normal position is On. Do not change selection unless instructed to do so by the Factory. Description of Operation LED Alarm Relay Normal Mode On Open Normal Mode with UPS Warning On Cycle (closed 5 sec., Open 25 sec.) CXM is non-functional Off Open Fault Retry Slow Flash Open Lockout Fast Flash Closed Over/Under Voltage Shutdown Slow Flash Open (Closed after 15 minutes) Test Mode - No fault in memory Flashing Code 1 Cycling Code 1 Test Mode - HP Fault in memory Flashing Code 2 Cycling Code 2 Test Mode - LP Fault in memory Flashing Code 3 Cycling Code 3 Test Mode - FP1 Fault in memory Flashing Code 4 Cycling Code 4 Test Mode - FP2 Fault in memory Flashing Code 5 Cycling Code 5 Test Mode - CO Fault in memory Flashing Code 6 Cycling Code 6 Test Mode - Over/Under shutdown in memory Flashing Code 7 Cycling Code 7 Test Mode - UPS in memory Flashing Code 8 Cycling Code 8 Test Mode - Swapped Thermistor Flashing Code 9 Cycling Code 9 Special Notes and Examples: - Slow Flash = 1 flash every 2 seconds - Fast Flash = 2 flashes every 1 second - Flash code 2 = 2 quick flashes, 10 sec. pause, 2 quick flashes, 10 sec. pause, etc. - On pulse 1/3 sec.; off pulse 1/3 sec. Page 4 CXM Electronic Heat Pump Control
Part I - CXM Electronic Heat Pump Control Safety Features The following safety features are provided to protect the compressor, heat exchangers, wiring and other components from damage caused by operation outside of design conditions. Anti-Short Cycle Protection- The control features a 5 minute anti-short cycle protection for the compressor. Note: The 5 minute anti-short cycle also occurs at power up. Random Start - The control features a 5-80 second random start upon power up. Extended Compressor Operation Monitoring - If the compressor relay has been on for 4 continuous hours, then the control will automatically turn off the compressor relay and wait the short cycle protection time. All appropriate safeties including the LP will be monitored during the off time. If all operation is normal, then if the compressor demand is still present, the control will turn the compressor back on. Fault Retry - In Fault Retry mode, the Status LED begins slow flashing to signal that the control is trying to recover from a fault input. The CXM control will stage off the outputs and then try again to satisfy the thermostat "Y" input call. Once the thermostat input calls are satisfied, the control will continue on as if no fault occurred. If 3 consecutive faults occur without satisfying the thermostat "Y" input call, then the control will go to Lockout mode. The last fault causing the lockout will be stored in memory and can be viewed by going into test mode. Note: If 1 Try is selected for FP1 and FP2, then there will be no retries for FP1 and FP2 faults. The control will only try one time for these faults. Lockout - In Lockout mode, the Status LED will begin fast flashing. The compressor relay is turned off immediately. Lockout mode can be soft reset via the thermostat Y input or can be hard reset via the disconnect. The last fault causing the lockout will be stored in memory and can be viewed by going into test mode. Lockout with Emergency Heat - While in Lockout mode, if W becomes active, then Emergency Heat mode will occur. High Pressure Switch - When the High Pressure Switch opens due to high refrigerant pressures, the Compressor relay is de-energized immediately since the High Pressure Switch is in series with the compressor contactor coil. The High Pressure Fault recognition is immediate as well. High Pressure Lockout Code = 2 Example: 2 quick flashes, 10 sec pause, 2 quick flashes, 10 sec. pause, etc. Low Pressure Switch - The Low Pressure Switch must be open and remain open for 30 continuous seconds during "on" cycle to be recognized as a Low Pressure fault. If the low pressure switch is open for 30 seconds prior to compressor power up it will be considered a low pressure (loss of charge) fault. The Low Pressure Switch input is bypassed for the initial 120 seconds of a compressor run cycle. Low Pressure Lockout Code = 3 Water Coil Freeze Protection (FP1) - The control will recognize an FP1 fault, during a compressor run cycle if: a) the thermistor temperature is below the selected freeze protection limit setting, AND b) the thermistor temperature is rising (getting warmer) at a rate LESS than 2 F per 30 second time period. The FP1 input is bypassed for the initial 120 seconds of a compressor run cycle. FP1 Lockout Code = 4 Air Coil Freeze Protection (FP2) - The control will recognize an FP2 fault, during a compressor run cycle if: a) the thermistor temperature is below the selected freeze protection limit setting, AND b) the thermistor temperature is rising (getting warmer) at a rate LESS than 2F per 30 second time period. The FP2 input is bypassed for the initial 120 seconds of a compressor run cycle. FP2 Lockout Code = 5 Condensate Overflow - The Condensate Overflow sensor must sense overflow levels for 30 continuous seconds to be recognized as a CO fault. Condensate Overflow will be monitored during compressor run cycle. CO Lockout Code = 6 Over/Under Voltage Shutdown - An Over/Under Voltage condition exists when the control voltage is outside the range of 18VAC to 31.5VAC. Over/Under Voltage Shutdown is self resetting in that if the voltage comes back within range of 18.5VAC to 31VAC for at least 0.5 seconds, then normal operation is restored. This is not considered a fault or lockout. If the CXM is in over/under voltage shutdown for 15 minutes, the alarm relay will close. Over/Under Voltage Shutdown Code = 7 Unit Performance Sentinel-UPS (patent pending) - The UPS feature warns when the heat pump is operating inefficiently. A UPS condition exists when: a) in heating mode with compressor energized, if FP2 is greater than 125 F for 30 continuous seconds, or b) in cooling mode with compressor energized, if FP1 is greater than 125 F for 30 continuous seconds, OR FP2 is less than 40 F for 30 continuous seconds. If a UPS condition occurs, the control will immediately go to UPS warning. The status LED will remain on as if the control is in Normal mode. (see "LED and Alarm Relay Operation Table" ). Outputs of the control, excluding LED and Alarm Relay, will NOT be affected by UPS. The UPS condition cannot occur during a compressor off cycle. During UPS warning, the alarm relay will cycle on and off. The cycle rate will be On for 5 seconds, Off for 25 seconds, On for 5 seconds, Off for 25 seconds, etc. Unit Performance Sentinel Warning Code = 8 CXM Electronic Heat Pump Control Page 5
Part I - CXM Electronic Heat Pump Control Swapped FP1/FP2 Thermistors - During Test mode, the control monitors to see if the FP1 and FP2 thermistors are in the appropriate place. If the control is in Test mode, the control will lockout, with Code 9, after 30 seconds if: a) the compressor is On in cooling mode and the FP1 sensor is colder than the FP2 sensor. Or, b) the compressor is On in heating mode and the FP2 sensor is colder than the FP1 sensor. Swapped FP1/FP2 Thermistor Code = 9. Diagnostic Features The Status LED on the CXM control advises the serviceman of the current status of the CXM control. The status LED can display either the current CXM mode or the last fault memory if in test mode. See Table 1 for a complete listing of codes. If the Fault type is "Primary" (HP, LP, FP1, FP2, or CO) then the Fault type will always be retained in memory (Primary faults will over write Secondary faults). If the Fault type is "Secondary" (Over/Under Voltage, UPS or Swapped FP1/FP2) then the Fault type will only be retained if there are no "Primary" faults in memory. The Secondary Fault types will not "overwrite" the Primary fault memory. Unit Operation Description PowerUp - The unit will not operate until all the inputs and safety controls are checked for normal conditions. Note: The compressor will have a 5 minute anti-short cycle delay at power-up. Standby - In Standby mode, Y and W inputs are not active. Inputs O and G may be active. Compressor will be off. Cooling - To enter Cooling mode, Y and O become active. The first time after power-up that there is a call for compressor, the compressor will follow a 5 to 80 second random start delay. There will also be a 5 minute compressor anti-short cycle protection time as well. After the random start delay and the anti-short cycle delay, the compressor relay is energized. On all subsequent compressor calls, the random start delay is omitted. Heating Stage 1 - To enter Heating Stage 1 mode, Y becomes active. The first time after power-up that there is a call for compressor, the compressor will follow a 5 to 80 second random start delay. There will also be a 5 minute compressor anti-short cycle protection time as well. After the random start delay and the anti-short cycle delay, the compressor relay is energized. On all subsequent compressor calls, the random start delay is omitted. Heating Stage 2 - To enter Heating Stage 2 mode, W becomes active (Y already active). The G input must be active or the W input is ignored. The Compressor relay remains on. EH1 is turned on immediately. With continuing Heating Stage 2 demand, EH2 will turn on after 10 minutes. The EH2 will not turn on (or will turn off if already on) if FP1 temperature is greater than 45 F and FP2 is greater than 110 F. Emergency Heat - In Emergency Heat mode, W becomes active while Y is not active. The G input must be active or the W input is ignored. EH1 is turned on immediately. With continuing Emergency Heat demand, EH2 will turn on after 5 minutes. The FP1 and FP2 temperatures do not effect emergency heat operation. Engineering Guide Specifications The following engineering guide specifications for the CXM control should be a part of all product submittals. CXM Control A microprocessor-based compressor controller (CXM) shall be provided to monitor and control unit operation. The control shall provide compressor and electric heater sequencing, high and low pressure monitoring, field selectable water and air coil freeze protection sensing, condensate overflow sensing, over/under voltage monitoring, and unit performance sentinel. The control shall also provide for water valve connection, a test mode, short cycle protection, random start-up, as well as fault LED, fault memory, and intelligent fault retry. The control shall employ a quick attach harness assembly for low voltage connections to the CXM control board to aid in troubleshooting or replacement. An integral terminal block with screw terminals shall be provided on the CXM control for all field low voltage connections. Table 1a: Fault Description Table Fault Fault LED Code Fault Condition No Fault In Memory 1 There has been no fault detected since the last power down/power up sequence High Pressure Switch 2 HP Open Instantly Low Pressure Switch or LOC 3 Freeze Protection Coax - FP1 4 Freeze Protection Air Coil - FP2 5 Condensate overflow 6 Over/Under Voltage Shutdown LP open for 30 continuous seconds before or during a call (bypassed for first 120 seconds) FP1 below Temp limit for 30 continous seconds (bypassed for first 120 seconds of operation) FP2 below Temp limit for 30 continous seconds (bypassed for first 120 seconds of operation) Sense overflow (grounded) for 30 continous seconds 7 (Autoreset) "R" power supply is <18VAC or >31.5VAC UPS Warning 8 Unit Performance Warning signal has Swapped FP1/FP2 9 FP1 and FP2 are in reversed positions Page 6 CXM Electronic Heat Pump Control
Part I - CXM Electronic Heat Pump Control CXM Electronic Heat Pump Control Page 7
Part II - DXM Electronic Heat Pump Control PART II DXM ELECTRONIC HEAT PUMP CONTROL DXM Overview The DXM Electronic Control is a robust, microprocessor based heat pump controller that is advanced and featureladen for maximum application flexibility. The DXM control has all of the basic CXM control features plus additional inputs and outputs which allow for extensive system capability. The DXM control has relay outputs for compressor, fan, fan speed, reversing valve, alarm relay, and 2 configurable accessory outputs. There are 3 LEDʼs which provide status indication. There are inputs for safety pressure switches, freeze protection thermistors, condensate overflow sensor, DIP switch selection inputs, thermostat inputs, night setback inputs, and emergency shutdown input. There are also 2 communications ports: one for communications with DXM dual compressor heat pumps, and another for communications with DXM slaved heat pumps. CM Part Number: 17B0002N01 DXM Control Board Physical Dimensions and Layout General Operating Parameters The following are general operating parameters for the DXM control: Operating Environment: -40 F to 176 F and up to 95% relative humidity, non-condensing. Storage Environment: -40 F to 185 F and up to 95% relative humidity, non-condensing. Power Requirements: DXM only power draw - - Normally 8 VA draw at 24VAC - Maximum 12 VA draw at 24VAC. A dedicated 24VAC, 50-60Hz, 1Ph, 40VA transformer minimum is required for typical WSHP application. Relay and Connection Contact Ratings: The following relays are mounted on the DXM control: Compressor Relay: 40VA at 24VAC Alarm Relay: 28VA at 24VAC Reversing Valve: 28VA at 24VAC Accessory Relay 1: 28VA at 24VAC Accessory Relay 2: 28VA at 24VAC Fan Enable Relay: 1 HP at 240VAC Fan Speed Relay: 1 HP at 240VAC Connection ratings on the DXM control: A terminal: 20VA at 24VAC. Larger solenoid valve draw should be used with accessory relays. Grounding: The control board is grounded through two of the metal standoffs. 5" P1 Y1 Y2 W1 O/W2 G R C AL1 C R R C Sig P5 Com2 Sig DXM 17P0002N01 C P4 Com1 Fan Enable (240Vac) N.O. Fan Speed (240Vac) N.O. Com Com N.C. 3/8 standoff 7" AL2 R NSB C ESD OVR H A R NO1 NC1 COM NO2 NC2 COM R P3 P2 Alarm Relay Facttory Use JW4 AL2 Dry Acc1 Relay Acc2 Relay Micro U2 Off Micro U1 On Status 1 HP HP Test LP LP Fault FP1 FP1 FP2 FP2 RV Relay RV RV CO 12 CO P7 Test Jumpers JW3 - FP1 Low Temp 1 24Vdc JW2 - FP2 Low Temp EH1 JW1 - LP Norm. Open 4 EH2 P6 Off On Comp Relay CCG CC 6 1/2" Factory low voltage molex connection for unit harness Factory low voltage molex connection for electric heat harness S1 S2 1.62 5 5 1/2" 4 Mounting Screws #6 sheet metal screw 1 long Page 8 DXM Electronic Heat Pump Control
Part II - DXM Electronic Heat Pump Control Basic Control Features Anti-short cycle protection High and Low pressure cutouts High and Low voltage cutouts Water Coil freeze protection Air Coil freeze protection Random Start Status LED, Test LED, and Fault LED Reset Lockout at unit or disconnect Intelligent Reset Condensate Overflow sensor Test Mode Electric Heat Outputs Accessory Water Valve Connection Advanced Control Features Two accessory relays configurable for multiple applications Night setback with override capability Emergency shutdown capability Communications port for DXM dual compressor applications Communications port for DXM slave heat pump applications Intelligent fan speed capabilities Boilerless electric heat Removable thermostat connector for ease of installation and service Accepts heat pump (Y,O) or heat/cool (Y, W) thermostat types Accepts heat pump thermostats with O or B reversing valve control logic Dehumidistat input for advanced functions Field Selectable Inputs Test Mode Test Mode allows the service personnel to check the operation of the control in a timely manner. By momentarily shorting the test terminals, the DXM control enters a 20 minute Test Mode period in which all time delays are sped up 15 times. During Test Mode, the Test LED will turn on. For Diagnostic ease at the thermostat, the alarm relay will also cycle during test mode. The Alarm relay will cycle on and off similar to the fault LED to indicate a code representing the last fault, at the thermostat. Note: Code 1 indicates there is no fault in memory; stated differently, the control has not faulted since the last power-down to power-up sequence. Test mode can be exited by shorting the test terminals for 3 seconds. Test mode can also be entered and exited by cycling the G input, 3 times within a 60 second time period. During Test mode, the control monitors to see if the FP1 and FP2 thermistors are in the appropriate place. If the control is in Test mode, the control will lockout, with Code 9, after 30 seconds if: a) the compressor is On in cooling mode and the FP1 sensor is colder than the FP2 sensor. Or, b) the compressor is On in heating mode and the FP2 sensor is colder than the FP1 sensor. Retry Mode - If the control is attempting a retry of a fault, the status LED will slow fl ash (slow fl ash=one fl ash every 2 seconds) to indicate the control is in process of retrying. Note: In the following field configuration options, jumper wires should be clipped ONLY when power is removed from the DXM control. Water Coil Freeze Protection Limit Setting - Jumper 3 (JW3-FP1 Low Temp) provides field selection of temperature limit setting for FP1 to be 30 F or 10 F. Not Clipped=30 F. Clipped=10 F. Air Coil Freeze Protection Limit Setting - Jumper 2 (JW2- FP2 Low Temp) provides field selection of temperature limit setting for FP2 to be 30 F or 10 F. Not Clipped=30 F. Clipped=10 F. Alarm Relay Setting - Jumper 4 (JW4-AL2 Dry) provides field selection of Alarm Relay terminal AL2 to be jumpered to 24VAC or to be dry (no connection). Not Clipped=AL2 connected to R. Clipped=AL2 dry contacts (no connection). Low Pressure Normally Open Jumper 1 (JW1-LP Norm Open) Provides field selection for Low Pressure input to be Normally Closed or Normally Open. Not Clipped = LP Normally Closed. Clipped = LP Normally Open. DIP Switches Note: In the following field configuration options, DIP switches should only be moved when power is removed from the DXM control to insure proper operation. DIP Package #1 (S1) DIP Package #1 is 8 position and provides the following setup selections. DIP 1.1: Unit Performance Sentinel Disable - provides field selection to disable the UPS feature. On = Enabled. Off = Disabled. DIP 1.2: Compressor Relay Staging Operation - provides selection of Compressor Relay Staging Operation. The compressor relay can be selected to turn on with Stage 1 or Stage 2 call from the thermostat. This is used with Dual Stage units (2 compressors where 2 DXM controls are being used) or with Master/Slave applications. In Master/Slave applications, each compressor and fan will stage according to its appropriate DIP 1.2. If set to stage 2, the compressor will have a 3 second on-delay before energizing during a Stage 2 demand. Also, if set for stage 2, the Alarm relay will NOT cycle during Test Mode. On=Stage 1. Off=Stage 2. DIP 1.3: Thermostat Type (heat/cool) - provides selection of Thermostat Type. Heat Pump or Heat/Cool thermostats can be selected. When in Heat/Cool mode, Y1 is input call for Cooling Stage 1, Y2 is input call for Cooling Stage 2, W1 is input call for Heating Stage 1, and O/W2 is input call for Heating Stage 2. In Heat Pump mode, Y1 is input call for Compressor Stage 1, Y2 is input call for Compressor Stage 2, W1 is input call for Heating Stage 3 or Emergency Heat, and O/W2 is the input call for RV (heating or cooling dependent upon DIP 1.4). On=Heat Pump. Off=Heat/Cool. DXM Electronic Heat Pump Control Page 9
Part II - DXM Electronic Heat Pump Control DIP 1.4: Thermostat Type (O/B) - provides selection of Thermostat Type. Heat Pump Thermostats with O output on with Cooling or B output on with Heating can be selected. On=HP Stat with O output with Cooling. Off=HP Stat with B output with Heating. DIP 1.5: Dehumidifi cation Mode - provides selection of normal or dehumidification fan mode. In dehumidification mode, the Fan Speed relay will remain off during Cooling Stage 2. In normal mode, the Fan Speed relay will turn on during Cooling Stage 2. On=Normal fan mode. Off=Dehumidification mode. DIP 1.6: DDC Output at EH2 - DIP Switch 1.6 provides selection for DDC operation. If set to DDC Output at EH2, the EH2 terminal will continuously output the last fault code of the controller. If set to EH2 normal, then the EH2 will operate as standard electric heat output. On = EH2 Normal. Off = DDC Output at EH2. DIP 1.7: Boilerless Operation - provides selection of Boilerless Operation. In Boilerless mode, only the compressor is used for heating mode when FP1 is above the temperature specified by the setting of DIP 1.8. If DIP 1.8 is set for 50 F, then the compressor is used for heating as long as FP1 is above 50 F. Below 50 F, the compressor is not used and the control goes into Emergency Heat mode, staging on EH1 and EH2 to provide heating. If a thermal switch is being used in place of the FP1 thermistor, then only the compressor will be used for heating mode when the FP1 terminals are closed. If the FP1 terminals are open, then the compressor is not used and the control goes into Emergency Heat mode. On=normal. Off=Boilerless operation. DIP 1.8: Boilerless Changeover Temperature - provides selection of Boilerless changeover temperature setpoint. On=50 F. Off=40 F. Table 2: Accessory Relay 1 Configuration Dip 2.1 Dip 2.2 Dip 2.3 Acc1 Relay Option On On On Cycle with fan Off On On Digital NSB On Off On Water valve slow opening On On Off OAD Off Off Off Reheat option - Humidistat Off On Off Reheat option - Dehumidistat All other DIP combinations are invalid Table 3: Accessory Relay 2 Configuration Dip 2.4 Dip 2.5 Dip 2.6 Acc2 Relay Option On On On Cycle with compressor Off On On Digital NSB On Off On Water valve - slow opening On On Off OAD All other DIP combinations are invalid DIP Package #2 (S2) DIP Package #2 is 8 position and provides the following setup selections. DIP 2.1: Accessory1 relay personality - provides selection of Acc1 relay personality. See Table 2. DIP 2.2: Accessory1 relay personality - provides selection of Acc1 relay personality. See Table 2. DIP 2.3: Accessory1 relay personality - provides selection of Acc1 relay option. See Table 2. DIP 2.4: Accessory2 relay personality - provides selection of Acc2 relay personality. See Table 3. DIP 2.5: Accessory2 relay personality - provides selection of Acc2 relay personality. See Table 3. DIP 2.6: Accessory2 relay personality - provides selection of Acc2 relay option. See Table 3. DIP 2.7: Auto Dehumidifi cation Fan Mode or High Fan Mode - provides selection of Auto Dehumidification Fan Mode or High Fan Mode. In Auto Dehumidification Mode, the Fan Speed relay will remain off during Cooling Stage 2 IF the H input is active. In High Fan Mode, the Fan Enable and Fan Speed relays will turn on when the H input is active. On=Auto Dehumidification Mode. Off=High Fan Mode. DIP Switch 2.8: Factory Setting - Normal position is On. Do not change selection unless instructed to do so by the Factory. Safety Features The following safety features are provided to protect the compressor, heat exchangers, wiring and other components from damage caused by operation outside of design conditions. Anti-Short Cycle Protection - The control features a 5 minute anti-short cycle protection for the compressor. Note: The 5 minute anti-short cycle also occurs at power up. Random Start - The control features a 5-80 second random start upon power up. The random start delay will be present after a control power up and after returning from Night Setback or Emergency Shutdown modes. Extended Compressor Operation Monitoring - If the compressor relay has been on for 4 continuous hours, then the control will automatically turn off the compressor relay and wait the short cycle protection time. All appropriate safeties including the LP will be monitored during the off time. If all operation is normal, then if the compressor demand is still present, the control will turn the compressor back on. Fault Retry - In Fault Retry mode, the Status LED begins slow flashing to signal that the control is trying to recover from a fault input. The Fault LED will also begin flashing a code representing the last fault, which occurred. The DXM control will stage off the outputs and then try again to satisfy the thermostat call for compressor. Once the thermostat input calls are satisfied, the control will continue on as if no fault occurred. If 3 consecutive faults occur without satisfying the thermostat call for compressor, then the control will go to Lockout mode. The last fault causing the lockout will be stored in memory and is displayed by the Fault LED. Page 10 DXM Electronic Heat Pump Control
Part II - DXM Electronic Heat Pump Control Note: If 1 Try is selected for FP1 and FP2, then there will be no retries for FP1 and FP2 faults. The control will only try one time for these faults. Lockout - In Lockout mode, the Status LED will begin fast flashing. The Fault LED will be flashing a code representing the last fault, which occurred that caused the lockout. The compressor relay is turned off immediately. Lockout mode can be soft reset via the thermostat by removing the call for compressor, or can be hard reset via the disconnect. The last fault causing the lockout will be stored in memory and is displayed by the Fault LED. Lockout with Emergency Heat - If the DXM is configured for Heat Pump thermostat mode (see DIP 1.3), the DXM is in Lockout mode, and the W input becomes active, then Emergency Heat mode will occur during Lockout. High Pressure Switch - When the High Pressure Switch opens due to high refrigerant pressures, the Compressor relay is de-energized immediately since the High Pressure Switch is in series with the compressor contactor coil. The High Pressure Fault recognition is immediate as well. The Fault LED will immediately begin flashing Code 2 when a High Pressure Fault occurs. High Pressure Lockout Code = 2 Example: 2 quick flashes, 10-sec pause, 2 quick flashes, 10- sec. pause, etc. Low Pressure Switch - The Low Pressure Switch must be open and remain open for 30 continuous seconds during a compressor on cycle to be recognized as a Low Pressure fault. If the low pressure switch is open for 30 seconds prior to compressor power up it will be considered a low pressure (loss of charge) fault. The Low Pressure Switch input is bypassed for the initial 120 seconds of a compressor run cycle. The Fault LED will immediately begin flashing Code 3 when a Low Pressure Fault occurs. Low Pressure Lockout Code = 3 Water Coil Freeze Protection (FP1) -The control will recognize an FP1 fault, during a compressor run cycle if: a) the thermistor temperature is below the selected freeze protection limit setting, AND b) the thermistor temperature is rising (getting warmer) at a rate LESS than 2 F per 30 second time period. The FP1 input is bypassed for the initial 120 seconds of a compressor run cycle. The Fault LED will immediately begin flashing Code 4 when a FP1 Fault occurs. FP1 Lockout Code = 4 Air Coil Freeze Protection (FP2) - The control will recognize an FP2 fault, during a compressor run cycle if: a) the thermistor temperature is below the selected freeze protection limit setting, AND b) the thermistor temperature is rising (getting warmer) at a rate LESS than 2 F per 30 second time period. The FP2 input is bypassed for the initial 120 seconds of a compressor run cycle. The Fault LED will immediately begin flashing Code 5 when a FP2 Fault occurs. FP2 Lockout Code = 5 Condensate Overflow - The Condensate Overflow sensor must sense overflow levels for 30 continuous seconds to be recognized as a CO fault. Condensate Overflow will be monitored at all times. The Fault LED will immediately begin flashing Code 6 when a Condensate Overflow Fault occurs. Condensate overflow will be monitored during compressor run cycle. CO Lockout Code = 6 Over/Under Voltage Shutdown - An Over/Under Voltage condition exists when the control voltage is outside the range of 18VAC to 31.5VAC. Over/Under Voltage Shutdown is self-resetting in that if the voltage comes back within range of 18.5VAC to 31VAC for at least 0.5 seconds, then normal operation is restored. This is not considered a fault or lockout. If the DXM is in over/under voltage shutdown for 15 minutes, the alarm relay will close. Over/Under Voltage Shutdown Code = 7 Unit Performance Sentinel-UPS (patent pending) - The UPS feature warns when the heat pump is operating inefficiently. A UPS condition exists when: a) In heating mode with compressor energized, if FP2 is greater than 125 F for 30 continuous seconds, or b) In cooling mode with compressor energized, if FP1 is greater than 125 F for 30 continuous seconds, OR FP2 is less than 40 F for 30 continuous seconds. If a UPS condition occurs, the control will immediately go to UPS warning. The status LED will remain on as if the control is in Normal mode. (see "LED and Alarm Relay Operation Table"). Outputs of the control, excluding Fault LED and Alarm Relay, will NOT be affected by UPS. The UPS condition cannot occur during a compressor off cycle. During UPS warning, the Alarm Relay will cycle on and off. The cycle rate will be On for 5 seconds, Off for 25 seconds, On for 5 seconds, Off for 25 seconds, etc Unit Performance Sentinel Warning Code = 8 Swapped FP1/FP2 Thermistors - During Test mode, the control monitors to see if the FP1 and FP2 thermistors are in the appropriate place. If the control is in Test mode, the control will lockout, with Code 9, after 30 seconds if: a) the compressor is On in cooling mode and the FP1 sensor is colder than the FP2 sensor. Or, b) the compressor is On in heating mode and the FP2 sensor is colder than the FP1 sensor. Swapped FP1/FP2 Thermistor Code = 9. ESD The ESD (Emergency Shut Down) mode is utilized when the ERV (Energy Recovery Ventilator) option is applied to an RE series rooftop unit to indicate an ERV fault. A contact closure at the ERV unit will connect common to the ESD terminal, which will shut down the rooftop/erv units. The green status light will flash code 3 when the unit is in ESD mode. The ESD mode can also be enabled from an external common signal to terminal ESD (see Thermostat Inputs section for details). ESD mode = code 3 (green status LED) DXM Electronic Heat Pump Control Page 11
Part II - DXM Electronic Heat Pump Control Diagnostic Features The Status LED and Fault LED on the DXM control advises service personnel of the current status of the DXM control. The Status LED will indicate the current mode that the DXM control is in. The Fault LED will ALWAYS flash a code representing the LAST fault in memory. If there is no fault on memory, then the Fault LED will flash Code 1. See Table 4 for a complete listing of codes. Unit Operation Description Power Up The unit will not operate until all the inputs and safety controls are checked for normal conditions. Note: The compressor will have a 5-minute anti-short cycle delay at power-up. Standby/Fan Only In Standby mode, the compressor will be off. The Fan Enable, Fan Speed, and RV relays may be on if appropriate inputs are present. If there is a Fan 1 demand, then the Fan Enable relay will turn on immediately. If there is a Fan 2 demand, then the Fan Enable and Fan Speed relays will turn on immediately. Note: DIP1.5 (Dehum Fan Mode Select) has no effect upon Fan 1 and Fan 2 outputs. The RV relay will not directly track the input demands for RV, the DXM control will employ smart RV control. This ensures that the RV will only switch positions if the thermostat has called for a heating/cooling mode change. Heating Stage 1 In Heating Stage 1 mode, the Fan Enable and Compressor relays are turned on immediately. If configured as Stage 2 (DIP1.2=off), then the compressor and fan will not turn on until there is Stage 2 demand. The Fan Enable relay and Compressor relay are turned off immediately when the Heating Stage 1 demand is removed. The control reverts to Standby mode. If there is a Master/Slave situation or a Dual Compressor situation, all Compressor relays and related functions will track with their associated DIP1.2. Heating Stage 2 In Heating Stage 2 mode, the Fan Enable and Compressor relays remain on. The Fan Speed relay is turned on immediately. The Fan Speed relay is turned off immediately when the Heating Stage 2 demand is removed. The control reverts to Heating Stage 1 mode. If there is a Master/Slave situation or a Dual Compressor situation, all Compressor relays and related functions will track with their associated DIP1.2. Heating Stage 3 In Heating Stage 3 mode, the Fan Enable, Fan Speed and Compressor relays will remain on. EH1 output is turned on immediately. With continuing Heating Stage 3 demand, EH2 will turn on after 10 minutes. EH1 and EH2 are turned off immediately when the Heating Stage 3 demand is removed. The control reverts to Heating Stage 2 mode. During Heating Stage 3 mode, EH2 will be off (or will turn off if already on) if FP1 is greater than 45 F AND FP2 is greater than 110 F (FP2 greater than 110 F includes the condition that FP2 is shorted). This condition will have a 30-second recognition time. During Heating Stage 3 mode, EH1, EH2, Fan Enable and Fan Speed will be on if the G input is not active. Table 4: LED and Alarm Relay Output Table Description of Operation Status LED (green) Test LED (yellow) Fault LED (red) Alarm Relay Normal mode On - Off Open Normal mode with UPS On - Flashing Code 8 Cycle (closed 5 sec, open 25 sec) DXM is non-functional Off Off Off Open Fault Retry Slow Flash - Flashing fault code Open Lockout Fast Flash - Flashing fault code Closed Test Mode - On - - Night Setback Flashing Code 2 - - - ESD Flashing Code 3 - - - Invalid T-stat Inputs Flashing Code 4 - - - HP Fault Slow Flash - Flashing Code 2 Open LP Fault Slow Flash - Flashing Code 3 Open FP1 Fault Slow Flash - Flashing Code 4 Open FP2 Fault Slow Flash - Flashing Code 5 Open CO Fault Slow Flash - Flashing Code 6 Open Over/Under Voltage Slow Flash - Flashing Code 7 Open (closed after 15 minutes) Notes: a)"flashing Appropriate Code" means that the Fault LED will ALWAYS flash a code representing the LAST fault in memory. If there is no fault in memory, the Fault LED will flash code 1. b) Codes will be displayed with a 10 second Fault LED off period. c) Slow flash will be 1 flash per every 2 seconds. d) Fast flash will be 2 flash per every 1 second. e) On pulse 1/3 sec.; off pulse 1/3 sec. Page 12 DXM Electronic Heat Pump Control
Part II - DXM Electronic Heat Pump Control Emergency Heat In Emergency Heat mode, the Fan Enable and Fan Speed relays are turned on. EH1 is turned on immediately. With continuing Emergency Heat demand, EH2 will turn on after 5 minutes. EH1 and EH2 are turned off immediately when the Emergency Heat demand is removed. The Fan Enable and Fan Speed relays will turn off after a 60-second delay. The control reverts to Standby mode. During Emergency Heat mode, EH1, EH2, Fan Enable and Fan Speed will be on if the G input is not active. Cooling Stage 1 In Cooling Stage 1 mode, the Fan Enable, Compressor, and RV relays are turned on immediately. If configured as Stage 2 (DIP1.2=off), then the compressor and fan will not turn on until there is Stage 2 demand. The Fan Enable and Compressor relays are turned off immediately when the Cooling Stage 1 demand is removed. The control reverts to Standby mode. The RV relay remains on until there is a Heating demand. If there is a Master/Slave situation or a Dual Compressor situation, all Compressor relays and related functions will track with their associated DIP1.2. Cooling Stage 2 In Cooling Stage 2 mode, the Fan Enable, Compressor, and RV relays remain on. The Fan Speed relay is turned on immediately (see DIP1.5). The Fan Speed relay is turned off immediately when the Cooling Stage 2 demand is removed. The control reverts to Cooling Stage 1 mode. If there is a Master/Slave situation or a Dual Compressor situation, all Compressor relays and related functions will track with their associated DIP1.2. Night Low Limit (NLL) Staged Heating In NLL Staged Heating mode, the OVR input becomes active and is recognized as a call for Heating (OVR is an alternate means of calling for Heating mode). In NLL Staged Heating mode, the control will immediately go into Heating Stage 1 mode With an additional 30 minutes of NLL demand, the control will go into Heating Stage 2 mode. With another additional 30 minutes of NLL demand, the control will go into Heating Stage 3 mode. Special DXM Application Notes Generally the following applications are based upon configuring the accessory relays. Cycle with Fan - If Accessory relay 1 is configured to cycle with fan, Accessory relay 1 will be on any time the Fan Enable relay is on. Cycle with Compressor - If Accessory relay 2 is configured to cycle with compressor, Accessory relay 2 will be on any time the Compressor relay is on. Digital Night Setback - If an Accessory relay is configured for Digital NSB, the Accessory relay will be on any time the NSB input is connected to Ground C. Note: If there are no Accessory relays configured for Digital NSB, then the NSB and OVR inputs are automatically configured for mechanical operation. See Mechanical NSB operation below. Mechanical Night Set Back - When the NSB input is connected to Ground C, all thermostat inputs (G, Y1, Y2, W1, and O/W2) are ignored. A thermostat setback Heating call can then be connected to the OVR input. If the OVR input becomes active, then the DXM will enter NLL Staged Heating mode. NLL Staged Heating Mode would then provide heating during the NSB period. Water Valve/Slow Opening - If an Accessory relay is configured for Water Valve/Slow Opening, the Accessory relay will turn on 60 seconds prior to the Compressor Relay turning on. Outside Air Damper-If an Accessory relay is configured for OAD, the Accessory relay will normally turn be on any time the Fan Enable relay is on. But, following a return from NSB (NSB input no longer connected to Ground C ) to Normal Mode, the Accessory relay will not turn on for 30 minutes even if the Fan Enable relay is on. After this 30-minute timer expires, the Accessory relay will turn on if the Fan Enable relay is on. Thermostat Inputs Table 5 shows the resulting demand from differing combinations of inputs. Y1 - Y1 is the input for compressor stage 1 if DIP1.3=on. Y1 is the input for Cooling Stage 1 if DIP1.3=off. Y2 - Y2 is the input for compressor stage 2 if DIP1.3=on. Y2 is the input for Cooling Stage 2 if DIP1.3=off. W1 - If Y1 and Y2 are active and DIP1.3=on, then W1 is the input for Heating Stage 3. If Y1 and Y2 are not active and DIP1.3=on, then W1 is the input for Emergency Heat. If DIP1.3=off, then W1 is the input for Heating Stage 1. O/W2 - O/W2 is the input for Reversing Valve relay if DIP1.3=on and DIP1.4=on. O/W2 is the input for Heating Stage 2 if DIP1.3=off. O/W2 is the input for Heat Mode if DIP1.3=on and DIP1.4=off; this means that the thermostat outputs a B call when in Heating mode and does NOT have an O output. The DXM control will employ Smart RV control. This ensures that the RV will only switch positions if the thermostat has called for a heating/cooling mode change. G - G is the input for Fan Enable relay. NSB and Override - NSB is the input for Night Setback mode. When Digital NSB is selected via the Accessory relays DIPswitch inputs and the NSB input is connected to Ground C, then the appropriately configured Accessory relay is turned on to signal the digital thermostat to go to Night Setback Setpoints. Stated differently, when configured for Digital NSB mode, the Accessory relay directly tracks the NSB input. When Digital NSB is NOT selected via the Accessory relays DIPswitch inputs and the NSB input is connected to Ground C, then Y1, Y2, W1 and O/W2 and G are ignored. During this time period, if OVR is momentarily connected to 24VAC, then Y1, Y2, W1 and O/W2 and G are once again monitored for 2 hours. After the 2 hour Override period, the DXM reverts back to ignoring Y1, Y2, W1 and O/W2 and G, assuming the NSB input is still connected to Ground C. There will be a random start timer when coming back from NSB mode. DXM Electronic Heat Pump Control Page 13
Part II - DXM Electronic Heat Pump Control Note: The maximum number of DXM controls with daisychained "NSB" terminals is 75. Also, the maximum total wire resistance of the "NSB" wiring is 500 Ohms. ESD - ESD is the input for Emergency Shutdown mode. When the ESD input is connected to Ground C, all inputs are ignored and all outputs are turned off. There will be a random start timer when coming back from ESD. Note: The maximum number of DXM controls with daisy-chained "ESD" terminals is 75. Also, the maximum total wire resistance of the "ESD" wiring is 500 Ohms. OVR - OVR is the input for Night Setback Override or Night Low Limit Staged Heating input (NLL). When Digital NSB is NOT selected via the Accessory relays DIP switch inputs and NSB is connected to Ground C, then if OVR is momentarily connected to 24VAC (minimum 1 second) then the OVR input is recognized as a Night Setback Override signal and the DXM control reverts from Night Setback and begins monitoring thermostat inputs for heating and cooling calls for a 2 hour override period. If NSB is connected to ground "C", then if OVR is continuously connected to 24V AC, then the OVR input is recognized as a call for NLL staged heating and the control enters NLL staged heating. H - The H input function is determined by the setting of DIP2.7. If DIP2.7=on then the H input is defined as Automatic Dehumidification Mode and is used as an automatic counterpart to DIP1.5, meaning if H is connected to 24VAC then the Fan Speed Relay will not turn on during Cooling Stage 2. If H is not connected to 24VAC then the Fan Speed Relay will turn on during Cooling Stage 2. If DIP2.7=off then the H input is defined as High Speed Fan input and is used as an input to call for High Speed Fan. If the control is in normal operating modes such as Standby, Cooling or Heating AND the H input is connected to 24VAC, then the Fan Enable and Fan Speed relays will be on at all times (this operation is very similar to the G/Fan Enable operation). Table 5: Thermostat Inputs with resulting demands Other Outputs Table 12 displays input and output signals. Electric Heat Outputs EH1 and EH2 turn on whenever the DXM control is in the following modes: Heating Stage 3, Emergency Heat, and boilerless operation. Status LED The Status LED is green. The Status LED indicates what mode the DXM control is in. See Table 4: LED and Alarm Relay Operation. Test LED The Test LED is yellow. The Test LED will be on any time the control is in Test mode. See Table 4: LED and Alarm Relay Operation. Fault LED The Fault LED is red. The Fault LED ALWAYS flashes the corresponding code for the last fault that has occurred. If there is no fault in memory, then the fault LED will flash Code 1. If the Fault type is Primary (HP, LP, FP1, FP2, or CO) then the Fault type will always be retained in memory (Primary faults will over write Secondary faults). If the Fault type is Secondary (Over/Under Voltage, UPS or Swapped FP1/FP2) then the Fault type will only be retained if there are no Primary faults in memory. The Secondary Fault types will not overwrite the Primary fault memory. See Table 4: LED and Alarm Relay Operation. Communications There are two communications ports (Com1 and Com2) which provide robust communications to external DXM control boards via a simple noise resistant low speed protocol. Wiring to Com1 and Com2 does NOT require the use of shielded wiring for operation; standard thermostat wire can be used. Com1 Com1 is used to communicate thermostat and external calls to other DXM Master/Slave controls. In this configuration, up to 3 heat pumps can be controlled by one thermostat. Note: Each heat pump could potentially be a Dual Compressor unit thus there could be up to 6 DXM controls being controlled by one thermostat. However, only 1 DXM control in each heat pump will be daisychained on Com1. See schematic on page 16. The Master DXM control is defined as the DXM control, which is directly connected to the wall-mounted thermostat, time clock, fire alarm, and humidistat. The Master DXM communicates to the Slave DXM typical signals such as: Y1, Y2, W1, O/W2, G, NSB, ESD, OVR, and H. The Slave DXM controls should have no direct connections to any exterior devices such as thermostats, time clocks, fire alarms, humidistats, etc Page 14 DXM Electronic Heat Pump Control