SECTION 14-102.04 14-102.04/ 1 2007OC19 DESCRIPTION The heating, ventilation and air conditioning (HVAC) system is designed to optimize passenger comfort. The system regulates interior vehicle atmosphere, filters the return air and forces conditioned air to circulate throughout the vehicle s interior. See Figure 1. The heating system includes floor convectors, fans, an auxiliary heating unit used as an emergency unit, temperature sensors, air cleaners and a heating system control unit. The air conditioning system includes a roof-mounted air conditioning unit, a compressor and operator s controls. Coolant lines connect the heating elements of the HVAC unit, and the operator s controls, to the engine coolant system. See Figure 2. Refrigerant lines connect refrigerant elements of the HVAC unit to the A/C compressor. See Figure 3. Recover the refrigerant to prevent it from getting into the atmosphere, where it would be harmful to the ozone layer. It is a danger serious enough that federal laws have been established concerning the use of refrigerants and the certification of qualified technicians. OPERATION Four components are always found in any refrigeration system. These elements are: a compressor, which moves the refrigerant, a condenser coil, which removes heat from the refrigerant, an expansion valve, which meters the amount of refrigerant sent to the evaporation coil, an evaporation coil (with integrated heater coil), which picks up heat from the load. Interior air is drawn through the return air grille. This air passes through a filter, the evaporator coil and the heater coil, where it is dehumidified and cooled or heated depending on the mode of system operation. When the compressor starts to function, the pumping action of the compressor reduces the pressure in the suction line and evaporator coil, causing the refrigerant gas to flow into the compressor. Under compression, the refrigerant gas temperature and pressure increase. The compressor pumps this high-temperature and high pressure refrigerant gas onto the condenser. The outside air passing through the condenser coil is cooler than the temperature of the hot refrigerant gas. When this occurs, the refrigerant changes state from gas to liquid. The liquid refrigerant leaves the condenser and flows to the reservoir. The reservoir stores the liquid refrigerant to meet the various demands of the expansion valve. Figure 1 - Heat Distribution and Air Circulation
2007OC19 2 /14-102.04 1 FROM ROOF UNIT ENGINE TO ROOF UNIT 5 2 5 4 4 4 5 1. SOLENOID VALVE 2. DRIVER S BLOWER 3. DEFROSTER UNIT 4. DRAIN VALVES 5. CONVECTORS 5 3 02523 4 Figure 2 - Heating Line The refrigerant leaves the reservoir through the liquid line and flows through the filter-dryer, which removes moisture from the system. The expansion valve meters the liquid into the evaporator coil, the refrigerant picks up the heat from the air and causes the refrigerant inside the evaporator coil to boil and change to vapor. The air is cooled and returned to the vehicle. The compressor pumps the heated gas out of the evaporator coil and into the condenser coil causing the cycle to repeat itself. By removing heat from the vehicle faster than it can enter, the unit maintains the desired temperature. The A/C unit operates in three different modes: HEATING MODE Heating is controlled by the thermostat. A single signal opens all solenoid valves and starts the recirculating pump, the convectors and the blowers. VENT MODE When the desired temperature is obtained, fresh air enters the A/C unit and the evaporator fans run. The compressor clutch, the circulating pump and coolant valves remain closed. COOL MODE The cool mode automatically starts as soon as the temperature goes above the set point. The A/C compressor clutch is engaged, energizing the electrically operated solenoid valve, which controls the flow of the refrigerant. COMPRESSOR Figure 3 - Refrigerant Lines (Typical)
14-102.04/ 3 2007OC19 OPERATOR S ENVIRONMENT This section only gives a brief overview of the operator s controls. For additional details, see the Nova Bus Operator s Manual. OVERHEAD CONTROL PANEL The main interior climate control switches are located on the overhead control panel, over the driver s head. See the Operator s Manual. HEATER/DEFROSTER The driver's heater/defroster is located in the driver's area in the front dash panel. It consists of a motor with a fan, a radiator, an air cleaner, an air intake line with a control flap, a valve with a control lever, and a switch. The defroster is controlled through the front ventilation control panel, to the right of the driver. See Figure 4 and Table 1. See the System Checking and Maintenance heading of this section for the maintenance procedures. OPERATOR'S BLOWER A blower motor, mounted in the duct above the driver's window, provides additional air circulation to the operator's compartment through two adjustable air outlets below the duct. For more information, see the operator s manual. 1 2 3 4 See Table 1 Front Ventilation Control Panel for the corresponding numbers. Figure 4 - Front Ventilation Control Panel (Typical) ENGINE ENVIRONMENT COMPRESSOR See Figure 5. The most important part of the refrigeration system is the compressor. Its function is to pump the low pressure gas out of the evaporator so that a rapid and continuous boiling action is maintained in the coil. The low pressure gas is compressed and forced into the condenser coil where it is cooled by air passing through the coil. The high pressure and reduced temperature causes it to re-liquefy. The compressor is a six cylinder, open-drive reciprocating type and is driven by the motor shaft coupled to a v-shaped belt. It is attached to a support bracket mounted on the engine. See the System Checking and Maintenance heading of this section for the maintenance procedures. RECIRCULATING PUMP See the System Checking and Maintenance heading of this section for the replacement procedures. FRONT VENTILATION CONTROL PANEL N O NAME FUNCTION 1 Defroster fan knob This knob controls the defroster fan. In the 0 position (extreme left), the fan is off. The other positions control the operating speeds of the defroster fan. 2 Windshield and floor distribution control lever 3 Interior/exterior air intake control lever When turned to the left, this lever directs the flow of air 100% toward the windshield. If moved completely to the right, it directs air to the driver's feet up to a maximum of 50% of the total flow by acting on air direction flaps. This lever controls the mix of recirculated air (100% to the left) and outside air (100% to the right) flowing into the defroster by moving the vent under the defroster. 4 Heat control lever This lever controls the intensity of the defroster heat. It gradually opens the hot water valve on the defroster as it is moved to the right. In addition, at a certain position to the left, it acts on a switch that activates the backup heating system (when the fan switch is not in the 0 position). Table 1 Front Ventilation Control Panel
2007OC19 4 /14-102.04 COMPRESSOR TURNBUCKLE COMPRESSOR TENSIONER 02530 Figure 5 - Compressor Mounted in the Engine Bay SYSTEM CHECKING AND MAINTENANCE DEFROSTER This test must be performed indoors. CHECKING See Figure 4 and Table 1. 1. Check whether the filter is clean. Clean it by blowing compressed air through it or replace it as needed. 2. Check whether the air recirculation flaps move easily by operating the interior/exterior air intake control lever (3) of the front ventilation control panel. 3. Check whether the air direction flaps (floor/windshield) move easily by operating the windshield and floor distribution control lever (2) of the front ventilation control panel. This procedure must be performed in run and lights mode. 4. Check whether the contact of the switch on the liquid supply valve is made when the heat control lever (4) of the ventilation control panel is actuated. 5. Start the bus and turn the defroster fan knob (1) of the front ventilation control panel to the right at position 1. The fan is operating at low speed. 6. Check that there are no vibrations or abnormal noise. 7. Turn the defroster fan knob (1) of the front ventilation control panel to the right at position 2. The fan is operating at medium speed. 8. Turn the defroster fan knob (1) of the front ventilation control panel to the right at position 3. The fan is operating at fast speed. 9. Turn the defroster fan knob (1) of the front ventilation control panel to the left at position 0. The fan comes to a complete stop. FRONT DOOR VENTILATION FAN The knob also controls the front door ventilation fan. The knob has four positions. At the 0 position, the fan is not operating. The three others positions refer to three different operating speeds. CHECKING 1. Turn the front door ventilation knob (1) to the right at position 1. The fan is operating at low speed. 2. Turn the front door ventilation knob (1) to the right at position 2. The fan is operating at medium speed. 3. Turn the front door ventilation knob (1) to the right at position 3. The fan is operating at fast speed. 4. Turn the front door ventilation knob (1) to the left at position 0. The fan comes to a complete stop. LATERAL VENTILATION A three-position toggle switch is used to control the fan located over the operator s area.
14-102.04/ 5 2007OC19 TENSION NEW - 175 ± 5 LB (79 ± 2 KG) TENSION IN SERVICE - 150 LB (68 KG) TURNBUCKLE 02531 TENSIONER Figure 6 - Belt Tension Adjustment CHECKING 1. Push the switch to the normal postion. The fan is operating at a normal speed. 2. Push the switch to the fast postion. The fan is operating at high speed. 3. Check that there are no vibrations or abnormal noise. MAINTENANCE All heater/defroster functions are controlled by switches or by the potentiometer. Regular maintenance must include a periodic lubrication and cable and switch hook-ups adjustments. Seasonal replacement of the air filter is also required. All these components of the heater/defroster can be accessed by the defroster access door. COMPRESSOR See Figure 5. For installation and removal procedures, and for torque values, see the manufacturer s Service Manual, distributed by Nova Bus. CHECKING The compressor requires practically no maintenance other than making sure there is enough oil and refrigerant in the system at all times. The lubrication system of the compressor will fail if the system loses its charge of oil or refrigerant. Both oil and refrigerant must be circulating through the compressor whenever it is running to prevent serious damage to the unit. Check the compressor mounting bolts and alignment periodically. Check compressor drive belt tension. Check carefully for indications of oil or refrigerant leakage. Leaks should be remedied promptly to prevent excessive refrigerant and oil loss. When repairing the compressor or replacing parts, make sure the parts are clean and not nicked or scratched. During disassembly, clean and inspect all parts; and when reassembling, wrap them in a clean cloth to prevent marring the surface. Lubricate all parts with compressor oil during assembly; make sure they are installed in the same position as previously. BELT TENSION ADJUSTMENT The tension of a new belt is 175 ± 5 lb (79 ± 2 kg). The operating tension must never exceed 150 lb (68 kg). If the tension is insufficient, the compressor will not be driven at the correct speed and the efficiency of the unit will be diminished. The belt could also slip, which would damage the compressor pulley and clutch if the situation persists. If the tension is excessive, the main bearings will be subjected to an additional load and will wear prematurely. To adjust the tension, either tighten the turnbuckle, or adjust the tensioner, depending on the option installed, until you reach the desired tension. See Figure 6. During the first month of operation, check the belt tension each week. OIL LEVEL CHECK The compressor MUST be hot when touched before verifying the oil level. Check if the compressor oil is at the required level by looking at the sight glass on the left-hand side of the compressor. Make sure the oil level is in conformity with the requirements found in the manufacturer s service manual.
2007OC19 6 /14-102.04 1 2 4 6 8 10 11 12 13 14 3 5 7 9 1. SCREW 2. HOUSING 3. NUT 4. IMPELLER 5. WASHER 6. SPRING SEAL 7. CERAMIC SEAL 8. RUBBER SEAL 9. O-RING 10. SCREW 11. HOUSING 12. RECIRCULATING PUMP 13. CLAMP 14. BASE MOUNT 15. ELECTRICAL CABLES 15 Figure 7 - Typical Recirculating Pump Assembly See the manufacturer s Compressor Operation and service Manual, distributed by Nova Bus. RECIRCULATING PUMP See Figure 7. Assembly may vary according to customer order; see the Parts Manual. REMOVAL 1. Close the cut-off valves between the pump and the auxiliary heating unit. 2. Drain the heating system to a level slightly below the pump level using the drain valve found at the pump intake. 3. Detach the electrical cable connection from the pump (1). 4. Disconnect the water-antifreeze lines from the pump. REASSEMBLY Reassemble all the parts as shown in Figure 8. Reassemble the ceramic seal (7) and the spring seal (6) such that the hard side of the spring seal is in contact with the ceramic seal. INSTALLATION 1. Reassemble the pump. 2. Attach the lines firmly to the pump. 3. Close the drain valve. 4. Open the two cut-off valves. 5. Put the electrical cable connection (15) back in place and apply a layer of sealing material. 6. Fill the circuit with coolant. FRONT DISASSEMBLY 1. Clean the outside of the pump (12). 2. Hold the pump in a contour vice made of soft material. 3. Loosen the housing (2) of the pump body and remove the o-ring (9). 4. Loosen the nut (3) and detach the impeller (4) carefully, using two screwdrivers. 5. Remove the spring seal (6), the ceramic seal (7) and the rubber seal (8). 6. Inspect all parts and replace if necessary. Always replace the seals. HEATING SYSTEM VALVE Figure 8 - Heating System Valve
14-102.04/ 7 2007OC19 See section 09: Engine Cooling for the circuit filling procedures and the recommended coolant. 7. Check that the pump is operating properly and that there are no leaks. HEATING SYSTEM VALVE See Figure 8. From time to time, the diaphragm of the heating system valve gets clogged with mineral deposits from water and dirt and needs to be replaced. AIR CLEANERS There are nine air cleaners that can be cleaned or replaced as required. Their location in the bus compartment is as follows: Two air cleaners on the roof unit, attached to the return air grille. One air cleaner on the defroster, accessible from the front One air cleaner on each floor fan, for a total of six. They are accessible by lifting the grids under the chairs and held in place by Velcro, which may be cleaned with compressed air without disassembly. CONVECTORS Before proceeding, make sure a container is available for recovering the liquids that escape from the valve. 1. Depressurize the cooling system by opening the surge tank cap, accessible from the engine compartment. 2. Drain the passenger compartment circuit. See heading Draining the Coolant Circuit in this section. 3. Open the n o 3 and 4 road side (left-hand side) overhead lights. 4. Remove the four screws from the valve head. 5. Disconnect the electronic connectors from the valve. 6. Remove the valve head. 7. Remove the diaphragm from the valve. Note the orientation of the diaphragm tongue to reinstall the diaphragm properly. 8. Reinstall the diaphragm; make sure the orientation of the tongue is the same as it was before removal. 9. Install the valve head on the body of the valve. 10. Fill the cooling system. The heating units are comprised of blades and tubes. If the units must be replaced, they should either be detached from the flexible tubes or cut from the tubing, then welded with a solder of 95 % tin and 5 % antimony (MP5001 standard). The system must be drained of water before replacing these units, and the system must be bled and free of all leaks before being put back into operation. CHECKING 1. Remove the protective panels at the bottom and top of the bus compartment walls. 2. Open the exterior access doors of the motor. 3. Start the bus and leave the heating system in automatic mode for 15 minutes or long enough for the coolant to heat. 4. Inspect all of the welded joints of the copper pipes and all hose clamps. Look for leaks and seepage. 5. Pay particular attention to the connections located above the passengers. 6. Tighten the clamps of the flexible hoses on the roof unit. 7. Turn the bus engine off. 8. Check that all convectors are clean. Clean them with compressed air, if necessary. REPLACEMENT See section 09: Engine Cooling for the circuit filling procedures and the recommended coolant. A dirty convector transmits heat much less efficiently than one with clean blades. 11. Open the heating system to check if the system operates properly. 12. Check the level of the coolant and add if necessary.
2007OC19 8 /14-102.04 WATER DRAINAGE ON THE ROOF 1. Check whether the bottom of the roof unit s molded structure is clean. Remove all debris that might obstruct water drainage. 2. Pour a glass of water into each water drain pipe on the roof unit, and check whether the water flows to the ground through these pipes. 3. If this is not the case, clear the drain pipes by blowing compressed air through them. HEATING CIRCUIT DUCTS CHECKING FOR LEAKS IN THE SYSTEM Before adding coolant, always check for leaks in the heating system, using the following procedure. Liquid in the cooling system must be hot. WARNING: The electric system of the components involved must be operational before executing the following procedure. 1. Block the top of the cooling system drain (drain line of the surge tank) with a bolt and a collar. Use a 3/8 in (10 mm) bolt. 2. Connect the regulator to the quick connect fitting of the filling unit. 3. Make sure the main valve of the ventilation unit is open (request for heating). 4. Make sure the draining valve under the dashboard is closed. 5. Make sure the valves of the auxiliary heating unit pipes are open. 6. Connect the air hose to the regulator and open the valve (set to 9 psi [62 kpa] for the ISC engine and to 12 psi [83 kpa] for the ISL engine). 7. For vehicles equipped with the automatic filling system: hold the switch in the test/auto position with a tie wrap for a minimum of 10 minutes. WARNING: When the switch is activated, the valve behind the control box should open. For vehicles equipped with the manual filling system: Press the knob under the quick connect fitting and maintain it pressed for a minimum of 10 minutes. 8. Check if a pressure drop occurred. If so, fix the leak(s). Use the leak detector to simplify the search or spray a soapy water solution. COOLANT CIRCUIT DRAINING PASSENGER COMPARTMENT CIRCUIT ONLY The engine must be off to drain the coolant. 1. Close the cut-off valve at the auxiliary heating unit output and the return valve of the bus compartment to cut off the compartment circuit from the circuit around the engine. 2. Place the heat control lever of the front ventilation control panel (see Figure 5) at the extreme right position to open the front defroster butterfly valve. 3. To facilitate the flow of liquid when draining, open the two roof unit air drain cocks, located at the end of each heat exchanger. 4. Open the main drain valve, located at the front center of the bus, next to the defroster. Have a recovery container handy. 5. Open the two small drain valves located in the middle of the bus, at the floor convectors intake; one is on the right and one is on the left. To reach the valves, remove the protective panels at the bottom of the walls. have a funnel, hose and recovery container handy. 6. Open the drain valve located above the fuel filler neck, and recover the coolant. ENGINE ONLY, INCLUDING THE AUXILIARY HEATER 1. Close the cut-off valve at the auxiliary heater unit intake and the return valve of the bus compartment to cut off the bus compartment circuit from the circuit around the engine. 2. To facilitate the draining of the liquids, open the plug on the front of the surge tank to create a vent. 3. Open the drain valve located under the retarder oil cooler. The retarder is located at the lowest point of the circuit. Have a recovery container handy.
14-102.04/ 9 2007OC19 COOLANT CIRCUIT FILLING If the recirculating pump has been drained, it must be filled with water before starting the system, since running it dry would be very damaging. See section 09: Engine Cooling for the circuit filling procedures and the recommended coolant. SPECIFICATIONS DEFROSTER Heat flow...67,000 Btu/h (19.6 kw) Air flow...500 cfm (235 l/sec) Motor... 24 V Current...14 A at 27 V Weight... 50 lb (22.7 kg) Thermal cutout... Closes the circuit at 298 o F (148 o C) FAN Bottom of front door (2 speeds)...150 cfm (70.7 l/sec) Driver's compartment (2 speeds)...150 cfm (70.7 l/sec) RECIRCULATING PUMP Heat flow...184 cfh (5200 l/h) at 0.2 bar Nominal voltage... 24 V Operating voltage...20-28 V Electrical consumption... 104 W Weight... 4.6 lb (2.1 kg) ROOF UNIT Heat flow...111,000 Btu (32.5 kw) Air flow... 2500-3600 cfm (1180-1700 l/sec) Motor... 24 V Current...105 A at 27 V Weight... 485 lb (220 kg) CONVECTORS Heat flow...40,000 Btu/h (11,72 kw) Radiator length... 47 in (1194 mm) Total max. air flow...600 cfm (283 l/sec) Motors... 24 V Current...4.5 A at 27 V Thermal cutout... 298 o F (148 o C)
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