Heating and Air Conditioning: Description and Operation
INTRODUCTIONBoth the heater and the heater/air conditioning systems share many of the same components. This information will deal with both systems together when component function is common, and separately when they are not.
For proper operation of the instrument panel controls, refer to the Owner's Manual provided with the vehicle.
All vehicles are equipped with a common A/C-heater unit housing assembly When the vehicle has only a heater system, the evaporator and recirculating air door are omitted.
An optional zone control HVAC unit is available. This unit has dual blend-air doors that can be regulated independently of each other. The temperature setting can be different from driver's side to passenger side. There is also a rear (aux.) heating and A/C system available when the vehicle is equipped with zone control.
SYSTEM OPERATION
A/C Control Panel:
Rear Blower Switch:
The auxiliary rear heating-air/conditioning unit is located in the right rear quarter panel. The rear heater A/C control operates in conjunction with the front heater A/C control. A four position two speed blower (override) switch is located on the front Heater A/C control panel. The operator can use the rear heater A/C blower switch to operate the blower, regardless of the rear control setting. In the OFF position, the rear control will not function. In the ON (RR) position, the rear control will function normally providing three speeds. The mode setting is controlled by the front A/C control panel.
Air from inside the vehicle is drawn into the air intake grille in the right rear quarter trim panel. The air enters the blower and is pushed through the heater core and A/C evaporator coil. The air direction, floor or overhead, is determined by the position of the driver's temperature control lever on the front HVAC system control. If the temperature control lever is below 20% heat, the auxiliary HVAC system airflow will come from the overhead air outlets. In between 20% and 80%, the airflow will remain in the last position selected. In other words, if the driver started out in full heat and then adjusted their temperature lever to 30% heat as they became comfortable, the rear air would come out the floor outlets the whole time.
Air Distribution Ducts
The air distribution ducts for the A/C, Heater, Defroster, and Second Seating Air Distribution are not serviceable in vehicle.
The only ducts that are serviceable in the vehicle are the side window demister ducts and the ducts that feed the front door outlets for the first rear passenger(s) seating.
A/C Pressure Transducer:
A/C Pressure Transducer
The A/C Pressure Transducer monitors the refrigerant gas pressure on the high side of the system. The transducer is located on the liquid line. The pressure transducer turns off the voltage to the compressor clutch coil when refrigerant gas pressure drops to levels that could damage the compressor. The transducer also is used to adjust condenser fan speeds and will turn off compressor at high refrigerant pressures. The pressure transducer is a sealed factory calibrated unit. It must be replaced if defective. 0-ring replacement is required whenever the pressure transducer is serviced. Be sure to use the 0-ring specified for the transducer.
Valve Service Ports:
A/C Service Ports
The A/C service port valve cores are located within the A/C lines. The High Side (Discharge) valve service port is located on the liquid line near the right frame rail. The Low Side (Suction) valve service port is located on the suction line near the compressor.
The High Side service port is a two piece port and is serviceable. The Low Side service port is not serviceable, the suction line would have to be replaced.
Rear Blower Speed Switch
The rear blower speed switch controls the rear blower with the choice of low and high speeds. When the switch is on it allows the blower speed switch located on the rear headliner to control rear blower speed. This switch will override the rear headliner blower switch. For operation instructions refer to the Owner's Manual. The rear blower speed switch is serviced separately from the A/C control module.
Compressor High-Pressure Relief Valve
The High Pressure Relief Valve prevents damage to the air conditioning system if excessive pressure develops. Excessive pressure can be caused by condenser air flow blockage, refrigerant overcharge, or air and moisture in the system.
The high pressure relief valve vents only a small amount of refrigerant necessary to reduce system pressure and then reseats itself. The majority of the refrigerant is conserved in the system. The valve is calibrated to vent at a pressure of 3450 to 4140 kPa (500 to 600 psi). If a valve has vented a small amount of refrigerant, it does not necessarily mean the valve is defective.
The High Pressure Relief Valve is located on the compressor manifold at the discharge passage.
NOTE: Special effort must be used to keep all R-134a system components moisture free. Moisture in the oil is very difficult to remove and will cause a reliability problem with the compressor.
Condensate Drain
Condensation from the evaporator housing is drained through the dash panel and on to the ground. This drain must be kept open to prevent water from collecting in the bottom of the housing.
If the drain is blocked condensate cannot drain, causing water to back up and spill into the passenger compartment. It is normal to see condensate drainage below the vehicle.
Engine Cooling System Requirements
To maintain ample temperature levels from the heating-A/C system, the cooling system must be in proper working order.
The use of a bug screen is not recommended. Any obstructions forward of the condenser can reduce the effectiveness of the air conditioning system.
Evaporator Probe
The Evaporator probe is located on the HVAC. The probe prevents evaporator freeze-up by signaling the Powertrain Control Module to cycle the compressor ON and OFF. The probe monitors the temperature of the refrigerant after expansion.
The evaporator probe is inserted into the evaporator between the coils. The probe is a sealed unit and cannot be adjusted or repaired. It must be replaced if found defective.
Handling Tubing And Fittings
Kinks in the refrigerant tubing or sharp bends in the refrigerant hose lines will greatly reduce the capacity of the entire system. High pressures are produced in the system when it is operating. Extreme care must be exercised to make sure that all connections are pressure tight. Dirt and moisture can enter the system when it is opened for repair or replacement of lines or components. The refrigerant oil will absorb moisture readily out of the air. This moisture will convert into acids within a closed system.
CAUTION:
- The system must be completely empty before opening any fitting or connection in the refrigeration system. Open fittings with caution even after the system has been emptied. If any pressure is noticed as a fitting is loosened, retighten fitting and evacuate the system again.
- A good rule for the flexible hose lines is to keep the radius of all bends at least 10 times the diameter of the hose. Sharper bends will reduce the flow of refrigerant. The flexible hose lines should be routed so they are at least 3 inches (80 mm) from the exhaust manifold. Inspect all flexible hose lines to make sure they are in good condition and properly routed.
- The use of correct wrenches when making connections is very important. Improper wrenches or improper use of wrenches can damage the fittings.
- The internal parts of the A/C system will remain stable as long as moisture free refrigerant and refrigerant oil is used. Abnormal amounts of dirt, moisture or air can upset the chemical stability. This may cause operational troubles or even serious damage if present in more than very small quantities.
- When opening a refrigeration system, have everything you will need to repair the system ready. This will minimize the amount of time the system must be opened. Cap or plug all lines and fittings as soon as they are opened. This will help prevent the entrance of dirt and moisture. All new lines and components should be capped or sealed until they are ready to be used.
- All tools, including the refrigerant dispensing manifold, the manifold gauge set, and test hoses should be kept clean and dry
HVAC Control Module:
HVAC Control Module
The HVAC control module regulates the operation of the various actuator motors. The actuator motors are used to move the mode, blend-air, and Recirculation doors.
The control module is included in the A/C control head located on the instrument panel. The control head includes the blower speed switch, rear wiper and washer operation, front & rear window defogger, recirculation door operation, and A/C compressor operation if equipped.
NOTE: The Recirculation function on the HVAC control module automatically defaults to the OFF position after a ignition key cycle. To reactivate the Recirculation function, the Recirculation button must be repressed.
Door Outlets:
Side Door Heater A/C Outlets
The driver's and passenger side doors have supplemental air outlets and duct work. The air is channeled from the instrument panel to the door duct and either to the lower floor or upper door outlets. The air can be adjusted to blow on the first rear passenger seat(s).
Demister Inlet:
Side Window Demister
The side window demisters direct air from the heater assembly. The outlets are located on the top forward corners of the front door panels. The demisters operate when the control mode selector is on FLOOR, MIX or DEFROST setting.
System Airflow
The system pulls outside (ambient) air through the cowl opening at the base of the windshield. Then it goes into the plenum chamber above the heater-A/C unit housing. On air conditioned vehicles, the air passes through the evaporator. At this point the air flow can be directed either through or around the heater core. This is done by adjusting the blend air door with the TEMP control on the control head. An optional zone control HVAC control module is available. This unit has dual blend-air doors that can be regulated independently of each other. The temperature setting can be different from driver's side to passenger side. After the air passes the blend-air door(s), the air flow can then be directed from the Panel, Floor, and Defrost outlets. Air flow velocity can be adjusted with the blower speed selector switch on the control head.
Ambient air intake can be shut off by closing the recirculating air door. This will recirculate the air that is already inside the vehicle. This is done by depressing the RECIRC. button on the control head. On air conditioned vehicles, moving the control to Mix or Defrost depresses the A/C button and will engage the compressor. This will send refrigerant through the evaporator, and remove heat and humidity from the air before it goes through the heater core.
CAUTION: In cold weather, use of the Recirculation mode may lead to excessive window fogging. The Recirculation mode is automatically deactivated in Mix and Defrost modes to improve window clearing operation.
System Oil Level
It is important to have the correct amount of oil in the A/C system to ensure proper lubrication of the compressor. Too little oil will result in damage to the compressor. Too much oil will reduce the cooling capacity of the system and consequently result in higher discharge air temperatures.
NOTE: The oil used in the compressor is ND8 PAG R134a refrigerant oil. Only refrigerant oil of the same type should be used to service the system. Do not use any other oil. The oil container should be kept tightly capped until it is ready for use. Tightly cap afterwards to prevent contamination from dirt and moisture. Refrigerant oil will quickly absorb any moisture it comes in contact with. Special effort must be used to keep all R-134a system components moisture4ree. Moisture in the oil is very difficult to remove and will cause a reliability problem with the compressor.
It will not be necessary to check oil level in the compressor or to add oil unless there has been an oil loss. Oil loss at a leak point will be evident by the presence of a wet, shiny surface around the leak.
Refrigerant Oil Level Check
When all air conditioning system is first assembled, all components (except the compressor) are refrigerant oil free. After the system has been charged with R134a refrigerant and operated, the oil in the compressor is dispersed through the lines and components. The evaporator, condenser, and filter- drier will retain a significant amount of oil, refer to the Refrigerant Oil Capacities chart. When a component is replaced, the specified amount of refrigerant oil must be added. When the compressor is replaced, the amount of oil that is retained in the rest of the system must be drained from the replacement compressor. When a line or component has ruptured and oil has escaped, the compressor should be removed and drained. The filter-drier must be replaced along with the ruptured part. The oil capacity of the system, minus the amount of oil still in the remaining components, can be measured and poured into the suction port of the compressor.
Example: On a dual system the evaporator retains 60 ml (2 oz). The condenser retains 30 ml (1 oz) of oil, and system capacity may be 220 ml (7.40 oz) of oil.
220 ml minus 90 ml = 130 ml (4.40 oz).
CAUTION: The refrigerant oil used in a R-134a A/C system is unique. Use only oils which were designed to work with R-134a refrigerant. The oil designated for this vehicle is ND8 PAG (polyalkalene glycol).
Servicing Refrigerant Oil Level
1. Using a refrigerant recovery machine, remove refrigerant from the A/C system.
2. Remove refrigerant lines from A/C compressor.
3. Remove compressor from vehicle.
4. From suction port on top of compressor, drain refrigerant oil from compressor.
Refrigerant Oil Capacities:
5. Add system capacity minus the capacity of components that have not been replaced through suction port on compressor. Refer to the Refrigerant Oil Capacity Chart.
6. Install compressor, connect refrigerant lines, evacuate, and charge refrigerant system.