Cab Heater and Air Conditioner, Water-Valve Controlled 83.02

Transcription

1 Preliminary Checks Before testing the operation of the air conditioning system, make the following checks: 1. Make sure the drive belt on the refrigerant compressor is not damaged and is correctly tensioned. Also check the compressor mountings for tightness. For instructions and other information, refer to the applicable refrigerant compressor section in this group. 2. Using a feeler gauge, check for correct refrigerant compressor clutch clearance. For instructions, refer to the applicable refrigerant compressor section in this group. 3. Check for broken, burst, or cut hoses. Also check for loose fittings on all parts. 4. Check for road debris buildup on the condenser coil fins. Using air pressure and a whiskbroom or a soapy spray of water, carefully clean off the condenser. Be careful not to bend the fins. 5. Check the color of the moisture indicator sight glass. If the color is blue, the refrigerant charge is dry. If the indicator is not blue, the system is contaminated with moisture. Recover the refrigerant, evacuate the system, replace the receiverdrier, and add a full refrigerant charge. 6. If there is not enough airflow, make sure that leaves or other debris have not entered the fresh air ports under the windshield. If debris have entered, it could clog the fins of the evaporator core and block airflow. Also be sure that all ducts are connected to the dash louvers and that the air-control flaps in the heater housing are moving properly. Performance Tests Following is a brief description of symptoms or conditions that could exist if something goes wrong with a refrigerant part. Air Conditioning Protection Unit (ACPU) NOTE: For more information about the ACPU, see Subject 050. The ACPU was installed on vehicles built before April 16, IMPORTANT: The ACPU control system consists of an electronic control module, high and low pressure switches, and the thermostatic switch. The control module monitors system conditions (low or high refrigerant charge) and controls the operation of the refrigerant compressor and the on-off fan drive. On Century Class Conventionals, the ACPU is located under the hood on the right side of the frontwall. On Argosy COEs, the ACPU is located on the right side of the vehicle behind the bumper. See Fig. 1 and Fig /14/98 1. ACPU Control Module 2. High Pressure Switch 3. Low Pressure Switch f Fig. 1, ACPU Mounting, Century Class Conventional The control module registers fault codes that warn of existing or impending problems in the air conditioning system. Table 1 provides a list of ACPU messages broadcast to the Instrumentation Control Unit (ICU) message display screen. Additionally, corresponding fault codes are provided. Use Table 1 to assist in troubleshooting the ACPU control system. For further information on system fault codes, see the section in Group 54 that discusses the Instrumentation Control Unit. Additionally, if ServicePro is available, a technician diagnostic routine is available covering the ACPU system. Century Class Trucks Workshop Manual, Supplement 23, December /1

2 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled 06/24/98 f ACPU Control Module 2. Low Pressure Switch 3. High Pressure Switch Cooling Check 1 Fig. 2, ACPU Mounting, Argosy COE When outside temperature and humidity are high, it will take longer to cool the cab, especially if the fresh air vents are left open. To determine if the air conditioner is cooling enough: 1. Set the engine speed at 1500 rpm. The engine fan should be on. 2. On Century Class Conventionals, open the hood. On Century Class Conventionals and Argosy COEs, open the cab doors. 3. Turn on the cab air conditioner. Set the controls at air conditioning (not max AC), fresh air (not recirculated air), and maximum blower speed. The compressor must be engaged during this test. 4. In the sleeper (if equipped), turn the temperature control knob all the way counterclockwise to COOL. Turn the fan control knob to position 3 (high). 5. Allow the system to run for at least 10 minutes (longer on hot and humid days). 6. In the cab, place a thermometer inside the center dash outlet. In the sleeper, place a thermometer inside the lower outlet. Make sure the controls are set so that air flows out of the duct being tested Record the temperatures and take pressure readings at the service valves. Record the readings again after three minutes. If the temperature readings have not stabilized, run the system for an additional three minutes and record the readings again. 8. Compare the measured temperature readings to the readings in the temperature/pressure tables in Specifications 400. If the duct s air temperature is higher than normal readings, the system isn t cooling enough. For possible causes, see the troubleshooting chart. Receiver-Drier The receiver-drier is normally at outside temperature. To the touch, the entire length of the unit should be the same temperature. If noticeable cool spots exist, replace the receiver-drier. A blockage at the inlet of the unit will cause high head pressures. Outlet blockages will cause low head pressures and little or no cooling. If the moisture indicator is pink or white (showing that the system is wet), the receiver-drier is saturated with moisture and must be replaced. Cooling System Although they are not physically connected, there is a close tie between a vehicle s air conditioner and its cooling system. Poor air conditioner cooling can be the result of a problem in the cooling system. If the cooling system does not work correctly, the heat of the engine will rise to abnormal levels. The added heat will transfer to the air conditioner, other underhood parts, and maybe make its way into the cab. The added heat makes it necessary for the air conditioner to work harder and, at the same time, it reduces the air conditioner s ability to cool down the air in the cab. Also, if the water regulating valve isn t closing all the way, heat will enter the cab, giving the impression that the air conditioning system is not working. Refer to Group 20 for cooling system troubleshooting and to the engine manufacturer s service manual for other details about cooling system problems. 300/2 Century Class Trucks Workshop Manual, Supplement 23, December 2004

3 ACPU Fault Codes and Tests ICU Text Message Problem MID SID FMI REFRIG PRES HIGH REFRIG PRES LOW Refrigerant charge above normal, high pressure Refrigerant charge is below normal, low pressure CLUTCH CIR OPEN Open circuit CLUTCH CIR SHORT Short circuit BAT VOLTAGE LOW Low battery voltage LO PRES SW OPEN Low pressure switch, open circuit HI PRES SW OPEN High pressure switch, open circuit HI PRES SW CALIBRT High pressure switch, life cycle exceeded Condenser is clogged, or the system is overcharged. Clean the condenser, then check system pressure. If okay, start the engine. After system pressure reaches 290 to 310 psi (1999 to 2137 kpa) on vehicles built before December 11, 1998 or 340 to 375 psi (2344 to 2586 kpa) on vehicles built from December 11, 1998 the fan should come on. If it doesn t, the fan hub could be damaged. Check system pressure. If the low-side pressure is below 35 psi (241 kpa) there is a loss of refrigerant charge. Perform a leak test. Repair any leaks, evacuate the system, replace the receiver-drier, and add a full charge of refrigerant. If the pressure is okay, use an ohmmeter to measure the resistance between the low pressure switch wires. Replace the switch if resistance is not kilo ohms. Check the wiring to the compressor clutch. Repair or replace as needed. Check the wiring to the compressor clutch. Repair or replace as needed. Check for excessive electrical loads, a damaged alternator, or a discharged battery. Repair or replace as needed. Check that the correct switches are installed. Check the switch wiring. Repair or replace as needed. Use an ohmmeter to measure the resistance between the low pressure switch wires. Replace the switch if resistance is not kilo ohms when the switch is open. Check that the correct switches are installed. Check the switch wiring. Repair or replace as needed. Use an ohmmeter to measure the resistance between the high pressure switch wires. Replace the switch if resistance is not kilo ohms when the switch is open. Replace the high pressure switch. After replacing the high pressure switch, reset the high pressure cycle to zero. For more information on resetting this parameter, see the Freightliner ServiceLink on-line help program. Century Class Trucks Workshop Manual, Supplement 23, December /3

4 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled ACPU Fault Codes and Tests ICU Text Message Problem MID SID FMI TSTAT CIR ERRATIC Evaporator coil thermostatic switch Table 1, ACPU Fault Codes and Tests Test the thermostatic switch following the instructions provided elsewhere in this subject. Expansion Valve Problems that start in the expansion valve show up as follows: when stuck closed, the evaporator coil and the expansion valve will be at outside temperature; when stuck open, both the coil and the valve will be extremely cold with frost or ice buildup. Because the expansion valve channels are very small, blockages in the system tend to be found here (the valve is very sensitive to contamination). Usually, the contaminant is water; less than a drop of water is all it takes to make the valve inoperative. When water reaches the valve, the extreme cold that results from the pressure drop freezes the water, forming a block of ice in the valve. After the system shuts down and the valve warms up, the ice melts, and the valve operates again, only to freeze-up when the moisture returns. On-and-off operation of the expansion valve means that the receiver-drier is not removing moisture from the system. These contaminants should cause the moisture indicator to turn white and then pink. Refrigerant Compressor Compressor problems usually show in one of four ways: abnormal noise, seizure, leakage, or low suction and discharge pressures. Resonant compressor noises are not causes for alarm. Irregular noise or rattles are likely to be caused by broken parts. To check for seizure, deenergize the magnetic clutch and see if the drive plate can be turned. If it won t turn, the compressor has seized. Low discharge pressure may be caused by not enough refrigerant, not enough belt tension, or a blockage somewhere in the system. These things should be checked before servicing the compressor. Evaporator The evaporator coils are basically trouble-free when airflow over the fins is not blocked. External or, less often, internal blockages will cause low suction pressure as well as little or no cooling. If a leak exists in the system, and it cannot be traced to other parts or fittings, suspect damage to one of the evaporator coils. Condenser The condenser is usually trouble-free. Normally, the temperature of the condenser outlet line is noticeably cooler than the inlet line. However, when road debris, such as leaves or dirt, build up, airflow over the condenser fins is blocked. Air is not able to absorb enough heat to turn the hot refrigerant gas into a liquid. High head pressures will result. In these cases, carefully clean off the outer surfaces of the condenser with compressed air or a soap and water solution. Be careful not to bend the fins. High head pressures will also occur if the condenser s tubing is abnormally bent, blocking the flow of refrigerant. Frost will appear at the point where the flow is restricted. Less common internal blockages (bits of foreign material or metallic grit buildup) will stop the flow of refrigerant. A quick test to check that poor system performance is caused by the condenser is to direct a spray of water onto the condenser while the system is running. If the air conditioner cools better because of the assist provided by the water, it is a sign that the condenser is not working. When troubleshooting a suspected condenser problem, remember that the problem may be caused by the radiator transferring high levels of heat to the condenser. Refer to Group 20 of this manual for cooling system troubleshooting and to the engine 300/4 Century Class Trucks Workshop Manual, Supplement 23, December 2004

5 manufacturer s service manual for other details about cooling system problems. Thermostatic Switch IMPORTANT: Before troubleshooting the thermostatic switch, be sure there is a full charge of refrigerant in the system. The compressor will not operate or will cycle too often if there is not enough refrigerant in the system. Quick or delayed cycling of the compressor may be caused by a thermostatic switch that is working, but is out of adjustment. If, after doing the tests below, the switch seems to be out of adjustment, replace it (the thermostatic switch cannot be recalibrated). 1. Be sure the compressor clutch is operating correctly. See the applicable refrigerant compressor section in this group. 2. Expose the evaporator coil. See Subject 180 for instructions. 3. Start the engine. Place the air conditioner control at its coldest setting. Turn on the air conditioner and the fan. 4. Place an accurate thermometer in contact with a tube on the evaporator coil. Be sure the thermometer is in good contact with the tube or you will get a wrong reading. When the temperature drops below 31 to 36 F ( 1 to 2 C), the compressor clutch should disengage and remain this way until the temperature rises to 39 to 44 F (4 to 7 C). 5. If the compressor did not engage when the temperature was above the accepted high range, do the following test: 5.1 Connect a voltmeter or a test light from one of the terminals on the thermostatic switch to ground. Repeat this test with the other terminal on the switch. 5.2 With the engine running and the air conditioner and blower on, both terminals will show voltage when the compressor should be engaged. One terminal will show voltage when the compressor should be disengaged. If there is no voltage, there is a problem in the electrical system from the batteries to the thermostatic switch. Check all circuits for the cause, and repair or replace the wiring or parts. In all other cases where the compressor is not engaging and disengaging properly, the thermostatic switch is the cause. Replace it with a new switch. 6. Shut down the engine and, to prevent accidental electric shock or shorting during dash assembling, disconnect the batteries. 7. Assemble the dash. See Subject 180 for instructions. Discharge Temperature Control (DTC) System The water regulating valve clicks when it opens and closes. The clicks can be used to confirm operation of the water valve. The valve is normally open (NO). When the potentiometer is turned to full cold and the cab is warm, the controller should send electricity to the solenoid that closes the water valve and stops coolant flow through the heater core. By listening for the sound of the valve opening and closing, the technician can determine if the water valve is operating. See Fig. 3 for the wiring schematic for the cab Discharge Temperture Control (DTC) module. See Table 2 for the electrical pinout descriptions of the DTC module. DTC Module Pinout Pin Electrical Function A Ground B Potentiometer Input ( ) Cold C Potentiometer Input (wiper) D Potentiometer Input (+) Hot E Solenoid Valve Output ( ) F Solenoid Valve Output (+) G Ignition +12V Table 2, DTC Module Pinout Use the troubleshooting procedures in Table 3 first. Use the troubleshooting procedures in Table 3 before using the procedures in Table 4. Use the troubleshooting procedures in Table 3 and Table 4 before using the procedures in Table 5. Century Class Trucks Workshop Manual, Supplement 23, December /5

6 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled 2 3 A GND B POT ( ) POT (CCW Cold) C DTC Module w/sensor C POT ( IN ) D POT ( + ) POT (Center Tap) POT (CW Hot) B A Temperature POT E Water Valve ( ) F Water Valve (+) G V IGN (12V) 1 B WV Solenoid (338W+) GND 98 B D GND V IGN (12V) A WV Solenoid (338W ) 09/19/2003 f Water Valve Solenoid (NO) 2. DTC Module With Sensor 3. Potentiometer Fig. 3, Cab Discharge Temperature Control Schematic Use the troubleshooting procedures in Table 3 before using the procedures in Table 6. Use the troubleshooting procedures in Table 3 before using the procedures in Table 7. See Table 8 for the electrical pinout descriptions of the DTC module. Line Restrictions A restricted suction line causes low suction pressure at the compressor and little or no cooling. A restriction in a line between the compressor and the expansion valve can cause high discharge and low suction pressure, and insufficient cooling. Usually, areas of ice or frost buildup mean a blockage. Parts that often freeze-up are probably corroded or inoperative and should be replaced. Parts (such as the expansion valve) that freeze-up once in a while may do so because of moisture in the system, which will cause the moisture indicator to turn white or pink. If this happens, recover the refrigerant charge, evacuate/recycle the system refrigerant, replace the receiver-drier, and install a new charge. Test No. 1 Measure voltage at the water valve by backprobing the connector. Voltage should be approximately 12V. CDTC System Initial Electrical Diagnosis Test Procedure Test Criteria Test Result Action Engine running Engine at normal operating temperature Temperature setting at full cold OK Go to test no. 2. Not OK Go to test no /6 Century Class Trucks Workshop Manual, Supplement 23, December 2004

7 Test No. 2 Measure voltage at the water valve by backprobing the connector. Voltage should be approximately 0V. CDTC System Initial Electrical Diagnosis Test Procedure Test Criteria Test Result Action 3 Repeat test no. 1 using a known good ground instead of water valve ground wire. Voltage should be approximately 12V. 4 Check the ground wire to the controller (terminal A). Engine running Engine at normal operating temperature Temperature setting at full hot Engine running Engine at normal operating temperature Temperature setting at full cold OK Not OK There are no apparent electrical problems with the system. With the engine at normal operating temperature, hot air should come from the vents when the temperature setting is full hot. When switched to full cold, cooler air should come from the vents within approximately 10 minutes. If the system does not operate as stated above, refer to one of the following: For little or no heat symptom, see Table 6. For blowing warm/hot air symptom, see Table 7. Perform tests in Table 4, CDTC System Temperature Potentiometer Test. OK Go to test no. 4. Not OK OK Not OK Table 3, CDTC System Initial Electrical Diagnosis Perform tests in Table 4, CDTC System Temperature Potentiometer Test. Perform tests in Table 4, CDTC System Temperature Potentiometer Test. Repair controller ground circuit. CDTC System Temperature Potentiometer Test Test No. Test Procedure Test Result Action 1 Disconnect the temperature potentiometer from the harness. Using an ohmmeter, measure the potentiometer resistance as follows: A to B (knob full CCW) 8000 to 12,000 ohms A to B (knob full CW) 40 to 60 ohms B to C (knob full CCW) 40 to 60 ohms B to C (knob full CW) 8000 to 12,000 ohms OK Not OK Go to test no. 2. Replace temperature potentiometer. NOTE: Resistance ranges are approximate. Century Class Trucks Workshop Manual, Supplement 23, December /7

8 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled CDTC System Temperature Potentiometer Test Test No. 2 Connect the potentiometer. Disconnect the harness from the controller. Using an ohmmeter, measure the potentiometer resistance through the harness pins at the controller as follows: C to D (knob full CCW) 8000 to 12,000 ohms C to D (knob full CW) 40 to 60 ohms B to C (knob full CCW) 40 to 60 ohms B to C (knob full CW) 8000 to 12,000 ohms Test Procedure Test Result Action NOTE: Resistance ranges are approximate. OK Not OK Table 4, CDTC System Temperature Potentiometer Test Temperature potentiometer and wires are okay. Perform tests in the table titled CDTC System Controller Test. Repair wiring between temperature potentiometer and CDTC controller. Test No. 1 Disconnect the harness from the CDTC controller. Measure voltage across pins A and G. Voltage should be approximately 12V. 2 Connect the harness to the CDTC controller. Measure voltage by backprobing one meter lead to pin F and placing the other lead to a known good ground. Voltage should be approximately 12V. CDTC System Controller Test Test Procedure Test Criteria Test Result Action 3 Measure voltage by backprobing pins F and E of the CDTC controller connector. Voltage readings should be: Slightly less than 12V when the control knob is full cold (CCW) 0V when the control knob is full hot (CW). Ignition on CDTC controller disconnected Ignition on CDTC controller connected Ignition on CDTC controller connected OK Go to test no. 2. Not OK Check power supply wire and fuse to CDTC controller. Check CDTC controller ground circuit. Repair as necessary. OK Go to test no. 3. Not OK OK Not OK Table 5, CDTC System Controller Test Replace the CDTC controller. No problem found. Repeat tests Table 3. Replace the CDTC controller. 300/8 Century Class Trucks Workshop Manual, Supplement 23, December 2004

9 CDTC System Special Test-Symptom: Little or No Heat and Passes All Electrical Tests Test No. Test Procedure Test Result Action 1 Check to make sure that the coolant source from the OK Go to test no. 2. engine is connected to the inlet pipe on the water valve. Not OK Route hose to correct connections. 2 Check to make sure that the water inlet hose at the water valve is hot. OK Not OK Check for blocked heater core and repair as necessary. Check for closed heater hose shutoff valve. If okay or not present, repair engine cooling system as necessary. Table 6, CDTC System Special Test-Symptom: Little or No Heat and Passes All Electrical Tests CDTC System Special Test-Symptom: Blows Warm/Hot Air and Passes All Electrical Tests Test No. 1 Remove the water valve and visually inspect the inside of the outlet tube to see if the plunger is broken or if debris is preventing the plunger from seating properly. Test Procedure Test Result Action OK If the vehicle: Has a 2002 or newer Detroit Diesel engine, or Has an MBE engine, or If water pump pressure or flow is higher than a standard truck, then Install a water flow restrictor, part number RCV H (available in the PDCs). Install the flow restrictor in the heater hose between the engine and the inlet side of the water valve. IMPORTANT: Make sure the flow restrictor is installed so that the flow direction arrow is toward the water valve, which is the direction of coolant flow. Not OK If plunger is broken, replace the water valve. If debris is present, clean the cooling system. Table 7, CDTC System Special Test-Symptom: Blows Warm/Hot Air and Passes All Electrical Tests DTC Module Pinout Pin Electrical Function A Ground 2 B Potentiometer (CCW cold) 98U C Potentiometer (center tap) 98T D Potentiometer (CW hot) 98J E Water Valve ( ) 98X F Water Valve (+) 98W DTC Module Pinout Pin Electrical Function G Ignition Power (12V) 98N Table 8, DTC Module Pinout Fault Analysis Flow Chart See Fig. 4 for the fault analysis flow chart. Century Class Trucks Workshop Manual, Supplement 23, December /9

10 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled ICE BLOCKING EVAPORATOR Check for low suction pressure. Check thermo static switch. INSUFFICIENT COOLING NO OR LOW AIR FLOW Check blower operation. CHECK AIR FLOW BLOWER NOT OPERATING Check for blown circuit breaker, damaged blower switch, broken wire, loose connections, damaged blower motor. NORMAL BLOWER OPERATION Check for restriction or leakage in air ducts or clogged evaporator core. NORMAL AIR TEMPERATURE Check for air leaks through cab doors and windows. HIGH SUCTION PRESSURE DISCHARGE PRESSURE LOW NORMAL HIGH NORMAL AIR FLOW Inspect system for visual defects. Check air temperature. HIGH AIR TEMPERATURE NORMAL SUCTION PRESSURE Check compressor. Expansion valve stuck open, or thermostatic switch not working. DISCHARGE PRESSURE LOW Check for over charge or block age downstream of the measure ment point and before the expansion valve. NORMAL Check for belt tension, restriction in suction line, or compressor. Check seal around evaporator or therm ostatic switch. LOW SUCTION PRESSURE DISCHARGE PRESSURE LOW NORMAL TO HIGH 04/30/2003 System Tables Fig. 4, Fault Analysis Flow Chart Check for blockage upstream of the measurement point and before the compressor. Check for blockage downstream of the measurement point and before the expansion valve. f /10 Century Class Trucks Workshop Manual, Supplement 23, December 2004

11 Problem Little or No Airflow The blower is not operating. There are restrictions or leaks in the air ducts. Ice has formed on the evaporator coil. Problem Little or No Airflow Check for an open circuit breaker. An open circuit indicates a short in the electrical system, which must be located and repaired. Check the air conditioner relays for operation. Replace, as necessary. Make sure the blower motor switch is working. Replace, if necessary. Check the wiring to the blower motor. If any connections are loose, securely tighten them. Make sure the wiring conforms to the applicable diagram under Specifications 400. Check the blower motor for operation. Replace if sticking or otherwise inoperative. Check the resistor block. Replace, if necessary. CAUTION Never try to bypass the fuse in the resistor block. To do so could cause the blower motor to overheat, resulting in serious damage to the heater/ air-conditioning system. Examine all air ducts and remove any blockages. Stop any leaks or replace any portion where the leaks cannot be stopped. Defrost the evaporator coil before resuming operation of the air conditioner. Review "Performance Tests" in this subject for possible causes and corrective action. Problem Warm Airflow When the Air Conditioner Is On There is no refrigerant charge in the system. Moisture in the system. The refrigerant compressor is not operating. Ice has formed on the evaporator coil. Problem Warm Airflow When the Air Conditioner Is On Perform a leak test. Repair any leaks, evacuate the system, replace the receiver-drier, and add a full charge of refrigerant. If moisture is in the system, ice crystals may form at the expansion valve, blocking the flow of refrigerant (off and on). Recover the refrigerant charge, replace the receiver-drier, evacuate the system, and add a full charge of refrigerant. If the refrigerant charge is low, charge and leak test the system. Repair any leaks. The refrigerant compressor clutch or drive belt needs repair or replacement. For instructions, see the applicable refrigerant compressor section elsewhere in this group. Defrost the evaporator coil before resuming operation of the air conditioner. Review "Performance Tests" in this subject for possible causes and corrective action. Century Class Trucks Workshop Manual, Supplement 23, December /11

12 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled Problem Low Evaporator Coil Outlet Pressure (Low Compressor Suction Pressure) Problem Low Evaporator Coil Outlet Pressure (Low Compressor Suction Pressure) The expansion valve is not working. Replace the expansion valve. There are restrictions in the line to the Remove the line restrictions. expansion valve. There is an insufficient refrigerant charge in the system. Locate the leak. Recover the charge, replace the receiver-drier, and add a full refrigerant charge. Problem High Compressor Discharge Pressure Problem High Compressor Discharge Pressure The shutters are not opening. Replace the shutter solenoid valve, Air Conditioning Protection Unit high pressure switch, or both. Airflow through the condenser is restricted. Remove the debris from the condenser. There is an internal restriction in the Replace the condenser. condenser. Ice buildup on the condenser or a cool spot on the line from the condenser to the receiver-drier. Air is present in the system. Heavy frosting on the suction line suggests that the evaporator coil is flooded. The engine is overheated. Restriction in the compressor discharge line. Perform a leak test. Repair any leaks, evacuate the system, and add a full charge of refrigerant. Defrost the evaporator coil before resuming operation of the air conditioner. See the engine manufacturer s operations manual for corrective measures. Repair or replace the line. Problem Evaporator Outlet Air Temperature Increases as the Compressor Discharge Pressure Drops Problem Evaporator Outlet Air Temperature Increases as the Compressor Discharge Pressure Drops There are leaks in the system. Leak test the system. The expansion valve setting is too low. Replace the expansion valve. Add a full charge of refrigerant. Too much oil is in the system. An indication of this is clutch or belt slippage at governed engine speed. Check and remove excess refrigerant oil. For instructions, see the applicable refrigerant compressor section elsewhere in this group. Problem Compressor Operates Too Often or Continuously Problem Compressor Operates Too Often or Continuously There is too little refrigerant in the system. Perform a leak test. Repair any leaks, and add a full charge of refrigerant. 300/12 Century Class Trucks Workshop Manual, Supplement 23, December 2004

13 Problem Compressor Operates Too Often or Continuously Ice has formed on the evaporator coil. Defrost the evaporator coil before resuming operation of the air conditioner. Check the operation of the thermostatic switch, and replace as necessary. There is a restriction in the refrigerant Remove the restriction from the line. system. Dirt and debris are clogging the condenser Remove all dirt and debris from the condenser fins. fins. The thermostatic switch isn t working. Replace the thermostatic switch. Problem Quick or Delayed Cycling of the Compressor Problem Quick or Delayed Cycling of the Compressor The thermostatic switch operates, but is Replace the thermostatic switch. Do not attempt to adjust it. out of adjustment. Loss of refrigerant is causing a delayed Leak test and add a full charge of refrigerant. cycling of the compressor. Problem Temperature in the Cab Too Low or No Heat Problem Temperature in the Cab Too Low or No Heat The water regulating valve is not opened. Move the temperature control knob toward warm. The water regulating valve is not opening Adjust the water regulating valve cable. all the way. The water regulating valve is not working. Replace the water regulating valve. A heater hose is pinched or twisted. Repair or replace the heater hose. Coolant is leaking from the system. Check for leakage at the heater core, and at all hose connections from the heater core to the engine. Check the radiator coolant level, as instructed in the vehicle driver s manual, and add coolant, if necessary. Check and repair any leaks at the radiator. Dust or dirt is clogging the heater core Remove and clean the heater core. fins. Problem Condensed Water Is Leaking from the Air Conditioner Problem Condensed Water Is Leaking from the Air Conditioner The drain tubes are plugged. Clean the drain holes and drain tubes. Century Class Trucks Workshop Manual, Supplement 23, December /13

14 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled the Refrigerant System Using ACPU Fault Codes For ACPU faults accompanied by fault messages, Fig. 5 and Table 9 list faults that the ACPU is capable of detecting. The wording of the fault message display may vary depending on the level of software installed in the instrument cluster. Use ServicePro to clear fault codes. See Fig. 6 for the ACPU system schematic. Fault Code Definitions High Pressure: The high pressure condition is detected by monitoring high pressure switch activity after the fan has been engaged. This fault can be caused by fan drive failure, condenser airflow blockage, or refrigerant overcharging. High Pressure Switch Open: Indicates that the wiring to the high pressure switch is an open circuit. This can be caused by an unseated connector, a break in the wiring harness, or moisture intrusion into the connectors or switch. When continuity to the switch resumes, this fault becomes inactive. High Voltage: Indicates a high supply voltage condition (greater than 16 volts). This can be caused by a defective alternator, voltage regulator or surges on the supply line. The high voltage warning goes away when the supply voltage returns to normal (below 16 volts). Low Pressure: This is detected by monitoring the ambient temperature and activity of the low pressure switch. It indicates a loss of refrigerant. Low Pressure Switch Open: Indicates that the wiring to the low pressure switch is an open circuit. This can be caused by an unseated connector, break in the wiring harness, or moisture intrusion into the connectors or switch. When continuity to the switch resumes, this fault code becomes inactive. Low Voltage: Indicates a low supply voltage condition. This can be caused by a defective alternator, discharged batteries or excessive loads. The low voltage warning goes away when the supply voltage returns to normal (above 11 volts). 08/18/97 A/C SYST REFRIG PRES HIGH 190 S A/C SYST REFRIG PRES LOW 190 S A/C SYST LO PRES SW OPEN 190 S A/C SYST CLUTCH CIR OPEN 190 S A/C SYST CLUTCH CIR SHORT 190 S A/C SYST TSTAT CIR ERRATIC 190 S A/C SYST BAT VOLTAGE LOW 190 S A/C SYST HI PRES SW OPEN 190 S A/C SYST HI PRES SW CALIBRT 190 S f High Pressure Fault 2. Low Pressure Fault 3. Low Pressure Switch Open 4. Open Wire to Clutch 5. Shorted Clutch 6. Erratic Thermostatic Switch 7. Low Battery Voltage 8. High Pressure Switch Open 9. High Pressure Switch Life has Exceeded 260,000 Cycles Fig. 5, ACPU Fault Messages Open Clutch: If no current is sensed when the AC clutch is engaged, an open connection to the clutch coil is inferred. When continuity to the clutch resumes, this fault becomes inactive. If this fault is detected, the AC is held off for the remainder of the ignition cycle. Shorted Clutch: This is detected by excessive current flowing to the compressor clutch. This indicates /14 Century Class Trucks Workshop Manual, Supplement 23, December 2004

15 power ground ACPU 12V IGNIT GND RED BLACK F D FIREWALL HARNESS 97B GND H4 B1 MAIN CAB HARNESS 97B GND AF5 NA3 10A PDO21 PDM GND BUS IGNIT digital I/O digital I/O digital Input J1587+ J1587 THERMOSTAT PINK VIOLET GREEN A B C J1587+ J T B3 B4 H1 97T LC1 B11 LC1 B4 TO THERMOSTAT P2 CLUSTER (LEFT SIDE) output FAN REQUEST ORANGE G 234A ELEC ENG HARNESS TO ECM output A/C CLUTCH BLUE E (NOT USED) H 97C 97C A/C CLUTCH 3.3 OHMS NOMINAL analog Input HPx YELLOW 12V ENGINE HARNESS signal return HPx RETURN YELLOW/BLACK 2.49K HIGH PRESS analog Input LPx WHITE signal return LPx RETURN WHITE/BLACK 2.49K LOW PRESS 08/14/97 f541631a Fig. 6, ACPU System Schematic either a shorted clutch coil or shorted wiring to the clutch. If this fault is detected, the AC is held off for the remainder of the ignition cycle. Erratic Thermostatic Switch: The thermostatic switch input has been detected to be switching on and off at a rapid rate. This indicates a bad AC selector, fan switch, thermostatic switch, or intermittent connections in the wiring or connectors. High Pressure Switch Calibration: Cycle life of the high pressure switch has been exceeded (260,000 cycles). Replace the switch and reset the ACPU by pressing the HPX button in ServiceLink. NOTE: Use ServiceLink to clear fault codes. ACPU Table Century Class Trucks Workshop Manual, Supplement 23, December /15

16 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled ACPU Table Dash Message Definition Action See Fig. 7. High pressure fault. The system is exhibiting abnormal high pressure activity. Fan drive failure Inspect for proper operation of the solenoid valve/relay and/or related components. Blocked air flow Remove the restriction from the condenser. Refrigerant overcharge Recover refrigerant and charge to the manufacturer recommended specification. See Fig. 8. See Fig. 9. Low pressure fault. This is detected by monitoring the ambient temperature and the switching activity of the low pressure switch. Open in wiring to the low pressure switch. Indicates that the wiring to the low pressure switch is damaged. High pressure switch out of tolerance Fan circuit has not been turned on in the Engine Control Module Partial or total loss of refrigerant A damaged low pressure switch Unseated connector Break between wiring harness and pressure switch Moisture intrusion into the connectors or switch Incorrect pressure switch installed Perform steps 3.1 through 3.7 in the following section to test fan and compressor operation and replace the high pressure switch if necessary. Disconnect the main harness to the ACPU module. If the engine fan engages, replace the ACPU module. If the engine fan doesn t engage, check the fan circuit in the ECM, and have the ECM programmed to accept ACPU input. Check the system for leaks. Disconnect the low side pressure switch connector and measure the resistance value of the switch. If the resistance shows 2490 ohms, the switch is operating properly, if resistance shows less than 5 ohms, replace the switch. NOTE: This check must be done with the switch installed, the ignition in the off position, and the system properly charged. Check the connectors at the module and the pressure switch for loose pins. Using an ohmmeter, probe the white and white/black pins of the module harness. Resistance should read 2490 ohms with the switch installed and proper charge. Check seals and inspect wires for hole punctures. Install the correct pressure switch. 300/16 Century Class Trucks Workshop Manual, Supplement 23, December 2004

17 ACPU Table Dash Message Definition Action See Fig. 10. Open wire to the A/C clutch. Detected by inadequate current A break in the wiring between the ACPU through the compressor clutch. If no module and the A/C current is sensed when the A/C compressor clutch drive is turned on, an open connection to the clutch coil is indicated. See Fig. 11. See Fig. 12. See Fig. 13. See Fig. 14. See Fig. 15. Shorted wire or A/C clutch. Detected by excessive current through the compressor clutch. Erratic evaporator thermostatic switch. The thermostat input has been detected to be switching on and off at a rapid rate. Low system voltage. Indicates voltage has dropped below 11.0 volts. Open in wiring to the high pressure switch. Indicates that the wiring to the high pressure switch is damaged. Cycle life of the high pressure switch has been exceeded. Poor electrical contact between the compressor and the vehicle ground No clutch output from the ACPU This means either a shorted clutch coil or shorted wiring to the clutch No clutch output from the ACPU An erratic power signal between the A/C cab controls and the ACPU module Possibly caused by a defective alternator, discharged batteries or excessive electrical loads Unseated connector Break between wiring harness and pressure switch Moisture intrusion into the connectors or the switch Incorrect pressure switch installed High pressure switch has exceeded more than 260,000 cycles Use an ohmmeter to check the wiring for continuity. Using an ohmmeter, test the resistance between the clutch and the compressor, and between the compressor and the engine block. If necessary, loosen the mounting on the compressor and retighten it to repair the contacts. Replace the ACPU with a binary switch. For instructions, see Service Bulletin With the use of an ohmmeter, check the resistance of the clutch coil. If the reading is less than 2.8 ohms, replace the clutch. Replace the ACPU with a binary switch. For instructions, see Service Bulletin Check for a bad A/C-On switch, thermostat, or an intermittent connection in the wiring or connection between the cab controls and the ACPU module (pin c). Check voltage at the control module harness by probing pins D (ground) and F (power). If voltage is less than 11.0 volts, start checking for voltage drops. Check connectors at the module and the pressure switch for loose pins. With the use of an ohmmeter, probe the yellow and yellow/black pins of the switch harness. Replace the switch if resistance is greater than 5 ohms. Check seals and inspect wires for continuity. Install the correct pressure switch. Replace the pressure switch with F/L part number Using ServiceLink, reset the high pressure cycle counter to zero. Century Class Trucks Workshop Manual, Supplement 23, December /17

18 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled ACPU Table Dash Message Definition Action No Dash Message. No Dash Message. No Dash Message. No Dash Message. Clutch is engaged, A/C is not cooling. A/C compressor is not engaging. A/C system is not cooling properly. Inoperative blower motor, or loose or broken compressor belts System air pressure is less than 60 psi (414 kpa) Cable to the heater control valve is disconnected or the valve is not completely closing Check for proper operation of the blower motors. Tighten or replace the compressor belts. Check for low air pressure. Check the cable at the heater control valve and behind the dash. Be sure the valve opens and closes completely. A/C compressor is not engaging. Engine rpm is less than 300 Check the cause of the low rpm. Table 9, ACPU Table NOTE: Use ServiceLink to clear fault codes. A/C SYST REFRIG PRES HIGH 190 S /13/97 A/C SYST CLUTCH CIR OPEN 190 S f /13/97 f Fig. 10, Open Wire to Clutch Fault Code Fig. 7, High Pressure Fault Code A/C SYST REFRIG PRES LOW 190 S /13/97 A/C SYST CLUTCH CIR SHORT 190 S f /13/97 f Fig. 11, Shorted Clutch Fault Code Fig. 8, Low Pressure Fault Code A/C SYST LO PRES SW OPEN 190 S /13/97 A/C SYST TSTAT CIR ERRATIC 190 S f /13/97 Fig. 9, Low Pressure Switch Open Fault Code f Fig. 12, Erratic Thermostatic Switch Fault Code the ACPU Use the following procedure for troubleshooting ACPU faults not accompanied by fault codes. 300/18 Century Class Trucks Workshop Manual, Supplement 23, December 2004

19 08/13/97 08/13/97 A/C SYST BAT VOLTAGE LOW 190 S Fig. 13, Low Battery Voltage Fault Code A/C SYST HI PRES SW OPEN 190 S f f Fig. 14, High Pressure Switch Open Fault Code 08/13/97 A/C SYST HI PRES SW CALIBRT 190 S f Fig. 15, High Pressure Switch Life Has Exceeded 260,000 Cycles Fault Code 1. Connect ServiceLink to the truck and download the fault codes. 1.1 Make repairs to correct existing fault codes. 1.2 Clear the fault codes using ServiceLink. 1.3 If the ACPU does not report on Service- Link, see Table Check for initial (lube) cycle. 2.1 With the main AC selector in the AC off position, start the truck. The compressor clutch should remain disengaged for about 15 seconds after starting the truck, then the compressor should engage for 15 seconds and shut off. This is the initial (lube) cycle. 2.2 If the compressor does not complete the initial (lube) cycle, see Table Test fan and compressor operation. 3.1 Apply the parking brakes and chock the tires. 3.2 Connect a refrigerant service cart to the truck air conditioning system. 3.3 Place cardboard in front of the air conditioning condenser so that it blocks all air from being drawn into the condenser. 3.4 Start the truck with the transmission in neutral, the main cab air conditioning selector switch in the on position, and the fan switch on high (position 4). 3.5 Check that the air conditioning compressor engages after about 15 seconds. 3.6 Check the reading of the high pressure gauge on the service cart when the fan comes on the first time. The fan should come on between 290 and 310 psi (1999 and 2137 kpa) on vehicles built before December 11, 1998 or between 340 and 375 psi (2344 and 2586 kpa) on vehicles built from December 11, This is the high pressure switch set point. The pressure may not reach the set point of the high pressure switch if the ambient air temperature is below 60 F (16 C). 3.7 If the compressor disengages after 15 seconds, see Table If the fan does not come on between 290 and 310 psi (1999 and 2137 kpa) on vehicles built before December 11, 1998 or between 340 and 375 psi (2344 and 2586 kpa) on vehicles built from December 11, 1998, see Table 13 and refer to step 3 in the ACPU Control Rules section of Service Bulletin Continue to observe the reading of the high pressure gauge on the service cart as the pressure falls. The compressor should re-engage at between 250 and 270 psi (1724 and 1862 kpa). This is the high pressure switch reset point. If the compressor does not re-engage at between 250 and 270 psi (1724 and 1862 kpa), see Table 14. Century Class Trucks Workshop Manual, Supplement 23, December /19

20 83.02 Cab Heater and Air Conditioner, Water-Valve Controlled Problem ACPU Not Reported on ServiceLink No power supply to the ACPU. Check the voltage between pins D (ground) and F (power) at the frontwall harness connector to the ACPU. If the voltage is less than 11.0 volts, start checking for voltage drops. Open J1587 circuit. Check for voltage between pins A (J1587+) and B (1587-) at the frontwall harness connector to the ACPU using a voltmeter in AC mode. The reading on the J1587 bus should be a constantly varying voltage between 0.5 and 5 volts. If there is no voltage signal on the J1587 bus with the ignition on, check for an open circuit in the J1587 bus. ACPU not responding. Replace the ACPU with a binary switch. For instructions, see Service Bulletin Table 10, Problem-ACPU Not Reported on ServiceLink Normal operation Active fault codes. Low air pressure. The high pressure switch is reporting a high pressure situation to the ACPU The low pressure switch is reporting a low pressure situation to the ACPU. Low or no battery power to the ACPU. Problem Compressor Doesn t Engage for Initial (Lube) Cycle If the AC is on, the compressor will operate longer than 15 seconds after the initial engagement. Use ServiceLink to download fault codes and perform necessary repairs. Check the air pressure. It must be above 60 psi (414 kpa) for the compressor to engage. Check the resistance between the leads to the high pressure switch. If it is greater than one ohm, check the air conditioning system pressures. If the high side pressure is below 250 to 270 psi (1724 to 1862 kpa), replace the high pressure switch and use ServiceLink to reset the HPX switch counter. Check the resistance between the leads to the low pressure switch. If it shows less than one ohm, check the air conditioning system pressures. If the low side pressure is above 34 psi (234 kpa), replace the low pressure switch. Check the voltage between pins D (ground) and F (power) at the frontwall harness connector to the ACPU. If the voltage is less than 11.0 volts, start checking for voltage drops. ACPU is not operating correctly. Replace the ACPU with a binary switch. For instructions, see Service Bulletin Table 11, Problem-Compressor Doesn t Engage for Initial (Lube) Cycle Problem The Compressor Doesn t Engage or Stays Engaged After the Initial (Lube) Cycle Active fault codes. Use ServiceLink to download fault codes and perform necessary repairs. High pressure switch reporting a high pressure situation to the ACPU. No power from the thermostat to the ACPU. Check resistance between the leads to the high pressure switch after the initial (lube) cycle. If the resistance is greater than one ohm and the pressure on the high side of the system is less than 250 to 270 psi (1724 to 1862 kpa), replace the high pressure switch and use ServiceLink to reset the high pressure switch counter. With the AC on, check for voltage between pins D (ground) and C (thermostat) at the frontwall harness connector to the ACPU. If the voltage is less than 11.0 volts check the circuit from the main cab HVAC selector switch, through the thermostatic switch, to the ACPU. 300/20 Century Class Trucks Workshop Manual, Supplement 23, December 2004

21 Problem The Compressor Doesn t Engage or Stays Engaged After the Initial (Lube) Cycle The thermostatic sensor detects an evaporator freeze condition. Determine if the freeze condition should exist. Refer to the steps for the thermostatic switch in this subject. The ACPU is not operating correctly. Replace the ACPU with a binary switch. For instructions, see Service Bulletin Table 12, Problem-The Compressor Doesn t Engage or Stays Engaged After the Initial (Lube) Cycle Fault code. Temperature too cold. Low refrigerant charge. Fan does not engage. Fan request lead is grounded. The set point of the high pressure switch is incorrect. Problem The Fan Doesn t Engage at the Set Point Check ServiceLink for fault codes, make necessary repairs, and clear fault codes with ServiceLink. If the ambient temperature is too cold (60 F [16 C] or below) the high side pressure may not reach the high pressure set point. If the system does not reach the high pressure set point, there may not be a proper charge in the air conditioning system. Disconnect the main connector to the ACPU and start the engine. If the fan does not come on immediately check to see if the fan request lead from the ACPU to the engine control module is grounded. Replace the high pressure switch and use ServiceLink to reset the HPX switch counter. The ACPU is not operating correctly. On increasing pressure, if the fan does not come on before the compressor shuts off, the ACPU is not operating correctly. Replace the ACPU with a binary switch. For instructions, see Service Bulletin Table 13, Problem-The Fan Doesn t Engage at the Set Point Problem The Compressor Doesn t Re-Engage at the Reset Point Fault code. Check ServiceLink for fault codes, make necessary repairs, and clear fault codes with ServiceLink. The reset point of the high pressure switch is incorrect. The thermostatic sensor detects an evaporator freeze condition. Replace the high pressure switch and use ServiceLink to reset the high pressure switch counter in the ACPU. Determine if a freeze condition should exist. Refer to the information on the thermostatic switch in this subject. The ACPU is not operating correctly. Replace the ACPU with a binary switch. For instructions, see Service Bulletin Table 14, Problem-The Compressor Doesn t Re-Engage at the Reset Point Century Class Trucks Workshop Manual, Supplement 23, December /21