Heating and Air Conditioning: Description and Operation
HEATING & AIR CONDITIONING - SERVICE INFORMATIONDESCRIPTION
COOLING SYSTEM REQUIREMENTS
To maintain the performance level of the Heating & Air Conditioning System, the engine cooling system must be properly maintained. Any obstructions in front of the radiator or condenser will reduce the performance of the Air Conditioning and Engine Cooling Systems.
The engine cooling system includes the heater core and the heater hoses. Refer to Cooling before attempting any service to the Engine Cooling System.
HEATER AND AIR CONDITIONER
WARNING: THE AIR CONDITIONING SYSTEM CONTAINS REFRIGERANT UNDER HIGH PRESSURE. SEVERE PERSONAL INJURY MAY RESULT FROM IMPROPER SERVICE PROCEDURES. REPAIRS SHOULD ONLY BE PERFORMED BY QUALIFIED SERVICE PERSONNEL.
AVOID BREATHING THE REFRIGERANT AND REFRIGERANT OIL VAPOR OR MIST. EXPOSURE MAY IRRITATE THE EYES, NOSE, AND/OR THROAT. WEAR EYE PROTECTION WHEN SERVICING THE AIR CONDITIONING REFRIGERANT SYSTEM. SERIOUS EYE INJURY CAN RESULT FROM DIRECT CONTACT WITH THE REFRIGERANT. IF EYE CONTACT OCCURS, SEEK MEDICAL ATTENTION IMMEDIATELY.
DO NOT EXPOSE THE REFRIGERANT TO OPEN FLAME. POISONOUS GAS IS CREATED WHEN REFRIGERANT IS BURNED. AN ELECTRONIC LEAK DETECTOR IS RECOMMENDED.
IF ACCIDENTAL SYSTEM DISCHARGE OCCURS, VENTILATE THE WORK AREA BEFORE RESUMING SERVICE. LARGE AMOUNTS OF REFRIGERANT RELEASED IN A CLOSED WORK AREA WILL DISPLACE THE OXYGEN AND CAUSE SUFFOCATION.
THE EVAPORATION RATE OF R-134a REFRIGERANT AT AVERAGE TEMPERATURE AND ALTITUDE IS EXTREMELY HIGH. AS A RESULT, ANYTHING THAT COMES IN CONTACT WITH THE REFRIGERANT WILL FREEZE. ALWAYS PROTECT THE SKIN OR DELICATE OBJECTS FROM DIRECT CONTACT WITH THE REFRIGERANT.
THE R-134a SERVICE EQUIPMENT OR THE VEHICLE REFRIGERANT SYSTEM SHOULD NOT BE PRESSURE TESTED OR LEAK TESTED WITH COMPRESSED AIR. SOME MIXTURES OF AIR AND R-134a HAVE BEEN SHOWN TO BE COMBUSTIBLE AT ELEVATED PRESSURES. THESE MIXTURES ARE POTENTIALLY DANGEROUS, AND MAY RESULT IN FIRE OR EXPLOSION CAUSING INJURY OR PROPERTY DAMAGE.
CAUTION: Liquid refrigerant is corrosive to metal surfaces. Follow the operating instructions supplied with the service equipment being used.
Never add R-12 to a refrigerant system designed to use R-134a. Damage to the system will result. R-12 refrigerant oil must not be mixed with R-134a refrigerant oil. They are not compatible. Do not use R-12 equipment or parts on the R-134a system. Damage to the system will result.
Do not overcharge the refrigerant system. This will cause excessive compressor head pressure and can cause noise and system failure.
Recover the refrigerant before opening any fitting or connection. Open the fittings with caution, even after the system has been discharged. Never open or loosen a connection before recovering the refrigerant. The refrigerant system must always be evacuated before charging.
Do not open the refrigerant system or uncap a replacement component until you are ready to service the system. This will prevent contamination in the system.
Before disconnecting a component, clean the outside of the fittings thoroughly to prevent contamination from entering the refrigerant system.
Immediately after disconnecting a component from the refrigerant system, seal the open fittings with a cap or plug.
Before connecting an open refrigerant fitting, always install a new seal or gasket. Coat the fitting and seal with clean refrigerant oil before connecting.
Do not remove the sealing caps from a replacement component until it is to be installed.
When installing a refrigerant line, avoid sharp bends that may restrict refrigerant flow. Position the refrigerant lines away from exhaust system components or any sharp edges, which may damage the line. Tighten refrigerant fittings only to the specified torque. The aluminum fittings used in the refrigerant system will not tolerate overtightening.
When disconnecting a refrigerant fitting, use a wrench on both halves of the fitting. This will prevent twisting of the refrigerant lines or tubes.
Refrigerant oil will absorb moisture from the atmosphere if left uncapped. Do not open a container of refrigerant oil until you are ready to use it. Replace the cap on the oil container immediately after using. Store refrigerant oil only in a clean, airtight, and moisture-free container.
Keep service tools and the work area clean. Contamination of the refrigerant system through careless work habits must be avoided.
A manual dual-zone temperature control type heating-air conditioning system is standard on this model.
This vehicle is equipped with a common HVAC housing assembly. The system combines Air Conditioning, Heating, and Ventilating capabilities in a single unit housing mounted under the Instrument Panel.
RESIDUAL ENGINE HEAT SYSTEM (REST)
The Residual Engine Heat System (REST) system enables the vehicle to be heated with the Ignition "OFF". The REST switch (4) in the Heater-A/C Controls activates this system.
REFRIGERANT SYSTEM SERVICE PORT
NOTE: Unique service port coupler sizes are used on the R-134a system to ensure that the refrigerant system is not accidentally contaminated by the use of the wrong refrigerant (R-12), or refrigerant system service equipment.
The two refrigerant system service ports are used to charge, recover/recycle, evacuate, and test the air conditioning refrigerant system.
The high pressure service port (1) is located on the liquid line near the front of the engine compartment behind the front grille.
The low pressure service port (1) is located on the suction line on the left side of the engine compartment near the shock mounting.
OPERATION
HEATER AND AIR CONDITIONER
Outside fresh air enters the vehicle through the cowl top opening at the base of the windshield (1), and passes through a plenum chamber to the HVAC housing. Air flow can then be adjusted by the blower motor (2) speed switch on the A/C Heater Control Panel. The fresh air then travels through the evaporator (6) and the heater core (5) then out into the vehicle through the side and floor vents (3-4).
It is also important to keep the air intake openings clear of debris because leaf particles and other debris that is small enough to pass through the cowl plenum screen can accumulate within the HVAC housing. This closed, warm, damp and dark environment created within the HVAC housing is ideal for the growth of certain molds, mildews and other fungi. Any accumulation of decaying plant matter provides an additional food source for fungal spores, which
can enter the housing with the fresh air. Excess debris, as well as objectionable odors created by decaying plant matter and growing fungi can be discharged into the passenger compartment during HVAC system operation.
AIR CONDITIONING
The A/C Compressor (8) is driven by the engines accessory drive belt. The A/C compressor (8) compresses the gaseous refrigerant (7) which heats up and flows into the condenser (6). The heat resulting from the compression is absorbed from the refrigerant by the surface of the condenser (6). As the refrigerant cools down it liquefies becoming a high-pressure liquid (4). As the refrigerant (4) flows through the receiver/ drier (5) it is purified of chemical and mechanical impurities. It then travels to the expansion valve (3) which sprays the cooled, low pressure liquid (4) into the evaporator (1), located in the fresh air flow. The refrigerant (4) evaporates in the evaporator (1). This evaporation process absorbs heat from the fresh air flowing across the system of tubes and honeycombs, therefore cooling the air that is blown into the passenger compartment. The low pressure gas then returns to the A/C compressor.
The moisture in the fresh air is condensed out and the condensation drained to the outside through a drain in the HVAC housing. The air is dried. The A/C compressor sucks in the refrigerant which has become gaseous due to the absorption of heat and compresses it again. When the engine is running and with blower switched on, cooled air can flow into the passenger compartment through various outlet openings. The intensity of cooling depends on the passenger compartment temperature set and the blower output.
The mode control on the A/C Heater Control Panel is used to direct the conditioned air to the selected system outlets. The mode control switches directs engine vacuum to control the mode doors, which are operated by vacuum actuators. The mode control switches electrical current to control the mode doors, which are operated by actuators.
- Mode Control (1)
- Passenger Temperature Control (2)
- Air Conditioning Button (3)
- REST Button (4)
- Driver's Temperature Control (5)
- Fan Control (6)
- Rear Defogger Button (7)
HEATER SYSTEM
The Water Pump (7) pumps coolant through the engine (3). There the coolant absorbs heat from the engine (3), heating up the coolant. Then the heated coolant flows through into the Heater Core (4) where the heat is transferred to the air in the passenger compartment. The coolant flowing through the Heater Core (4) is controlled by a Coolant Circulation Valve (6) located in the coolant return. The coolant can be controlled separately for the left and right sides.
The coolant returns to the Water Pump (7) via the coolant return hose. A Coolant Circulation Pump (5) is installed between the Coolant Circulation Valve (6) and the Water Pump (7). The Coolant Circulation Pump (5) serves for maintaining a uniform flow of heating water through the Heater Core (4) even at low engine speeds and in the Residual Engine Heat Utilization (REST) mode. The major portion of the coolant flows from the engine (3) to the Thermostat (2) instead of flowing through the Heater Core (4). The Thermostat (2) routes the water through the radiator (8) or directly to the Water Pump (7) depending on the temperature.
In a blend-air system, a Blend Door controls the amount of unconditioned air (or cooled air from the Evaporator) that is allowed to flow through, or around, the Heater Core (3). A temperature control knob on the A/C Heater Control Panel determines the discharge air temperature by energizing the Blend Door Actuator, which operates the Blend Door. This allows an almost immediate control of the output air temperature of the system.
R.E.S.T. SYSTEM
The Coolant Circulation Pump pumps the heated coolant to the Heater Core when the engine is off. When the REST button (4) is pressed the temperature is controlled by the A/C Heater Control Module (in the same manner as when the Ignition is ON). The A/C Heater Control module switches the Coolant Circulation Pump on which drives the impeller via a magnetic clutch. A light in the switch will illuminate indicating that the REST system is active.
REST SYSTEM
The REST system is activated by a switch in the Heater-A/C Controls when the ignition is turned "OFF". This system circulates residual heat from the engine to the Heater Core. The coolant is recirculated by an auxiliary coolant pump mounted below the right front headlamp. The temperature is automatically adjusted according to the temperature setting in the Heater-A/C Controls. The REST system will automatically be shut off when:
- The Ignition Key is Turned "ON"
- After Approximately 30 Minutes of Operation
- If Battery Voltage Falls Below 11.5 Volts