Heating and Air Conditioning: Description and Operation
INTRODUCTIONBoth the heater and the heater/air conditioning systems share many of the same functioning 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.
HVAC Unit Housing:
To service the heater core or evaporator, the unit housing must be removed from the vehicle.
HEATER AND AIR CONDITIONING CONTROL
Both the heater-only and heater-A/C Systems use a combination of; electrical, cable, and vacuum controls. These controls provide the vehicle operator with a number of setting options to help control the climate and comfort within the vehicle. Refer to the owner's manual in the vehicle glove box for more information on the features, use, and suggested operation of these controls.
The heater-only or heater-A/C control panel is located to the right of the instrument cluster on the instrument panel. The control panel contains rotary-type knobs. There is a blower motor speed switch, mode control switch, temperature control, and airflow control.
The heater-only or heater-A/C control panel cannot be repaired. If faulty or damaged, the entire unit must be replaced. The control knobs and the illumination lamps are available for service replacement.
HEATER AND AIR CONDITIONING
Common Blend-Air HVAC (Heating, Ventilation, Air Conditioning) System - Typical:
All vehicles are equipped with a common heater-A/C housing assembly. The system combines air conditioning, heating, and ventilating capabilities in a single unit housing mounted under the instrument panel. On heater-only systems, the evaporator coil is omitted from the housing and replaced with an air restrictor plate.
Outside air enters the vehicle through the cowl top opening at the base of the windshield, and passes through a plenum chamber to the heater-A/C system blower housing. Air flow velocity can then be adjusted with the blower motor speed selector switch on the heater-A/C control panel. The air intake openings must be kept free of snow, ice, leaves, and other obstructions for the heater-A/C system to receive a sufficient volume of outside air.
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 heater-A/C housing. The closed, warm, damp and dark environment created within the heater-A/C 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 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 heater-A/C system operation.
The heater and optional air conditioner are blend-air type systems. In a blend-air system, a blend-air door controls the amount of unconditioned air (or cooled air from the evaporator on models with air conditioning) that is allowed to flow through, or around, the heater core. A temperature control knob on the heater-A/C control panel determines the discharge air temperature by moving a cable, which operates the blend-air door. This allows an almost immediate manual control of the output air temperature of the system.
The mode control knob on the heater-only or heater-A/C control panel is used to direct the conditioned air to the selected system outlets. The mode control switch uses a cable to control the mode door, while the recirculation air door is operated by a vacuum actuator motor.
On air conditioned vehicles, the outside air intake can be shut off by selecting the recirculation mode (Recirc) with the mode control knob. This will operate a vacuum actuated recirculating air door that closes off the outside fresh air intake and recirculates the air that is already inside the vehicle.
The optional air conditioner for all models is designed for the use of non-CFC, R-134a refrigerant. The air conditioning system has an evaporator to cool and dehumidify the incoming air prior to blending it with the heated air. This air conditioning system uses an evaporator probe to maintain minimum evaporator temperature and prevent evaporator freezing, and cycles the compressor clutch.
A/C REFRIGERANT LINES
Discharge Line
A/C Compressor Lines:
The discharge line is the line that goes from the compressor to the condenser. It has no serviceable parts except the rubber O-rings. If the line is found to be leaking or is damaged it must be replaced as an assembly.
Liquid Line
The liquid line is the line that goes from the condenser to drier. It has no serviceable parts except the rubber O-rings. If the line is found to be leaking or is damaged it must be replaced as an assembly.
Suction Line
The suction line is the large line that connects to the expansion valve and goes to the compressor. It also has a small line that goes to the filter/drier. The suction line uses a gasket on the expansion valve side and rubber O-rings on all other connections.
There are no serviceable parts on the suction line other than the rubber O-rings and expansion valve gasket. If the line is found to be leaking or is damaged it must be replaced as an assembly.
A/C SERVICE PORT VALVE CORES
A/C Service Port Valves:
The A/C service port valve cores are serviceable items. The high side valve is located on the filter-drier, and the low side valve is situated on the suction line, near the washer fluid reservoir filler.
BLOWER MOTOR RESISTOR
Blower Motor Resistor Block:
Blower Motor Resistors:
The blower motor resistor is located in the cowl, at the base of the windshield. There are two different resistor blocks depending on whether the vehicle is equipped with A/C or not. The blower motor resistors will get hot when in use. Do not touch resistor block if the blower motor has been running.
COMPRESSOR
The compressor used on this vehicle is a Nippondenso 10S17. This compressor uses an aluminum swash plate, teflon coated pistons and aluminum sleeveless cylinder walls.
NOISE
Excessive noise that occurs when the air conditioning is being used may be caused by:
- Loose bolts
- Mounting brackets
- Loose compressor clutch
- Excessive high refrigerant operating pressure
Verify the following before compressor repair is performed:
1. Compressor drive belt condition
2. Proper refrigerant charge
3. Thermal expansion valve (TXV) operating correctly
4. Head pressure is normal
COMPRESSOR FRONT SHAFT SEAL
The compressor front shaft seal is not serviceable. If a leak is detected at the shaft seal, the compressor must be replaced as a unit.
CONDENSATION DRAIN TUBE
Condensation that accumulates in the evaporator housing is drained from a tube through the dash and on to the ground. This tube must be kept open to prevent condensate water from collecting in the bottom of the housing.
The tapered end of the drain tube is designed to keep contaminants from entering the heater A/C unit housing. If the tube is pinched or 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. If the tube is damaged, it should be replaced.
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 can be replaced without having to remove the unit housing from the vehicle.
The evaporator probe is located in the unit housing and placed in the evaporator fins. The probe prevents evaporator freeze-up. This is done by cycling the compressor clutch OFF when evaporator temperature drops below freeze point. It cycles ON when the evaporator temperature rises above freeze point. The evaporator probe uses a thermistor probe in a capillary tube. The tube is inserted between the evaporator fins in the heater-A/C unit housing.
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 moisture4ree 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 every- thing 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.
HIGH PRESSURE CUT OUT SWITCH
High Pressure Cut Out Switch Location:
The high pressure cut out switch is located on the rear of the compressor. It turns off the compressor if the system pressure exceeds 3240 kPa (470 psi).
LOW PRESSURE CUT OFF SWITCH
Low Pressure Cut Off Switch:
The Low Pressure Cut Off Switch monitors the refrigerant gas pressure on the suction side of the system. The low pressure cut off switch is located on the expansion valve. The low pressure cut off switch turns off voltage to the compressor clutch coil when refrigerant gas pressure drops to levels that could damage the compressor. The low pressure cut out switch is a sealed factory calibrated unit. It must be replaced if defective.
SIDE WINDOW DEMISTERS
The demisters direct air from the unit housing through the outlets located on the top corners of the instrument panel. The demisters operate when the mode selector is anywhere between floor and defrost settings. Some air may be noticeable from the demister outlets when the mode selector is in the bi-level to floor positions.
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 unit housing. On air conditioned vehicles, the air passes through the evaporator. 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 instrument panel. The air flow can then be directed from the panel, floor and defrost outlets in various combinations using the mode selector. There are 17 different mode selections possible. Air flow velocity can be adjusted with the blower speed selector switch on the instrument panel.
On A/C equipped vehicles the ambient air intake can be controlled by opening and closing the recirculating air door. When placed in RECIRC air that is inside vehicle is removed continuously and recirculated through unit housing. Ambient air cannot be controlled on vehicles without A/C. The system uses outside air at all times.
The air conditioning compressor can be engaged by turning the fan switch counterclockwise from the off position. It can also be engaged by placing the mode control in the mix to defrost positions. This will remove heat and humidity from the air before it is directed through or around the heater core.
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 R-134a 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 moisture-free. 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
Refrigerant Oil Capacities:
When an air conditioning system is first assembled, all components (except the compressor) are refrigerant oil free. After the system has been charged with R-134a 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.
VACUUM CONTROL SYSTEM
A/C Vacuum Line:
Recirculation Air Door Vacuum Actuator:
The neon uses vacuum to operate only the recirculation door. All other controls are cable. When vacuum is supplied to the actuator, the door moves to the Recirculation position. The actuator is spring loaded so the door moves to the Outside-air position when there is no vacuum supplied. The operation of the door can be viewed by removing the blower motor and looking up into the unit inlet.
Normally, vacuum is supplied to the actuator by placing the Circulation control knob in the Recirculation position. The Mode and the circulation control are mechanically interlocked so the circulation control cannot be placed in the RECIRC position if the mode control is at or between the mix and defrost positions. Vacuum is supplied to the actuator only when circulation control is at the RECIRC position. If the circulation control is between the outside air position and RECIRC position the system will be in outside air. If the circulation control is in the RECIRC position and the mode control is moved from the floor to the defrost positions, the circulation control will move from the RECIRC position, to the outside air position beginning at the mix position. This is to prevent window fogging.