Part 1 of 2
HEATER AND AIR CONDITIONINGFig 1. Heating, Ventilation, Air Conditioning (HVAC) Unit Housing:
Both the standard heater-only and the optional heater/air conditioning systems share many of the same functional components. This will deal with both systems together when component function is common, and separately when they are not. Ail 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.
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 a low pressure cycling clutch switch mounted on the accumulator to maintain minimum evaporator temperature and prevent evaporator freezing by cycling the compressor clutch.
Other than the heater core, the evaporator and the blower motor and wheel unit, the internal components of the heater and air conditioning system unit housing are serviced only as a unit with the upper or lower housing unit. To service the heater core or evaporator, the unit housing must be removed from the vehicle and disassembled.
Fig.2 Common Blend-Air HVAC System - Typical:
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 b~ 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 bland 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 beater 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. Models with the optional heater-A/C system also have a recirculation air door within the unit housing, which is operated by a vacuum actuator motor. On air conditioned vehicles, the outside air intake can be shut off by selecting the recirculation mode with the air flow control knob. This will move the recirculation air door to close off the outside fresh air intake and recirculates the air that is already inside the vehicle. On models with the standard heater-only system, the use of outside air cannot be controlled. This system uses outside air at all times.
On air conditioned models, the air conditioning compressor is engaged by turning the blower control knob counterclockwise from the OFF position to any of the available blower speed settings. The compressor will also be engaged if the mode control knob is placed in or between the Mix or Defrost positions.
AIRFLOW DISTRIBUTION
Fig.3 HVAC Outlets:
Based upon the system mode selected, conditioned air can exit the standard heater-only or optional heater-A/C unit housing through one or a combination of the three main housing outlets: defrost, panel or floor. The defrost outlet is located on the top of the housing, the panel outlet is located on the face of the housing and the floor outlet is located on the bottom of the housing. Once the conditioned air exits the unit housing, it is further directed through molded plastic ducts to the various outlets in the vehicle interior. These outlets and their locations are as follows:
- Defroster Outlet - A single large defroster outlet is located in the center of the instrument panel top cover, near the base of the windshield.
- Side Window Demister Outlets - There are two side window demister outlets, one is located at each outboard end of the instrument panel top cover, near the belt line at the A-pillars.
- Panel Outlets - There are four panel outlets in the instrument panel, one located near each outboard end of the instrument panel facing the rear of the vehicle and two located near the top of the instrument panel center bezel.
- Front Floor Outlets - There are four front floor outlets, two located above each side of the floor panel center tunnel near the dash panel.
- Rear Floor Outlets - There are two rear floor outlets, one located on each side of the floor panel center tunnel near the front of each rear seat foot well.
Fig.4 HVAC Ducts:
The defroster outlet receives airflow from the unit housing through the molded plastic defroster duct, which is snapped onto the unit housing defroster outlet and secured by two tabs to mounting slots in the dash panel. The airflow from the defroster outlet is directed by fixed vanes in the defroster outlet grille and cannot be adjusted. The defroster outlet grille is integral to the instrument panel top cover.
The side window demister outlets receive airflow from the unit housing through the air outlet distribution duct, two molded plastic demister hoses and, on the right side only, an intermediate duct. The air outlet distribution duct is secured to the instrument panel with screws and receives airflow through the panel outlet of the unit housing. The airflow from the side window demister outlets is directed by fixed vanes in the demister outlet grilles and cannot be adjusted. The side window demister outlet grilles are integral to the instrument panel top cover.
The panel outlets also receive airflow from the unit housing through the air outlet distribution duct. Molded plastic panel outlet ducts and, on the left side only, an intermediate elbow direct airflow from the distribution duct to the outboard panel outlets, while a center air outlet duct directs airflow from the distribution duct to the two center panel outlets. The airflow from each of the panel outlets is adjustable. A knob in the center of each panel outlet grille is used in a joystick fashion to adjust a center diffuser that changes the airflow direction, and a knob on the outer edge of each panel outlet grille opens or closes a shutter to turn airflow on or OFF through that outlet.
The front and rear floor outlets receive airflow from the unit housing through the floor distribution duct. The front floor outlets are integral to the molded plastic floor distribution duct, which is secured to the bottom of the unit housing. A molded plastic rear seat duct elbow is fitted to the bottom of the floor distribution duct and directs airflow through a molded plastic duct beneath the carpet on the right side of the floor panel center tunnel to the right rear floor outlet. The right floor duct also features a crossover fitting that joins the right floor duct to the left floor duct over the top of the floor panel center tunnel to direct airflow to the left rear floor outlet. None of the floor outlets can be adjusted.
HEATER AND AIR CONDITIONING CONTROL
Fig.5 Heater-A/C Controls:
The standard heater-only or optional heater-A/C control panel is located to the right of the instrument cluster on the instrument panel. The heater-only control panel contains three rotary-type control knobs, while the heater-A/C control panel contains four. There are separate control knobs for the blower switch, the mode control switch, temperature control and, on the heater-A/C models, an air flow control knob.
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.
Refer to Instrument Panel Systems for the heater only or heater-A/C control panel and control knob service procedures.
Both the heater-only and heater-A/C systems use a combination of electrical, cable and, on heater-A/C equipped models, 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.
VACUUM CONTROL SYSTEM
Fig.5 A/C Vacuum Line:
Only models with the optional heater-A/C system have a vacuum control system. This system uses engine vacuum to operate the recirculation air door. The vacuum control system includes the following components:
- Vacuum harness - The vacuum harness is plastic tubing that carries engine vacuum from the source vacuum port in the engine compartment to the various other components of the system.
- Check valve - A one-way vacuum check valve is installed in the vacuum harness between the source vacuum port in the engine compartment and the heater-A/C control.
- Switch - A vacuum switch is integral to the heater-A/C control on the instrument panel.
- Actuator - A vacuum actuator is mounted to the outside of the heater-A/C unit housing near the recirculation air door.
Fig.7 Recirculation Air Door Vacuum Actuator:
When engine vacuum is supplied to the actuator, the actuator linkage moves the recirculation air door to the recirculation-air position. The actuator is spring loaded so that the recirculation air door moves to the default outside-air position when there is no vacuum supplied. Vacuum is switched to the actuator by placing the air flow control knob in the Recirculation position. The mode and the air flow control are mechanically interlocked so that the air flow control cannot be placed in the Recirculation position if the mode control knob is in or between the Mix and Defrost positions. The check valve prevents the vacuum in the vacuum control system from being depleted during low engine vacuum operating conditions.
Fig.8 HVAC Unit Housing:
BLOWER MOTOR
The blower motor is a 12-volt, direct current motor that spins a squirrel cage-type blower wheel that is secured to the blower motor shaft. The blower motor and wheel are located near the right end of the heater-only or heater-A/C housing unit in the passenger compartment below the right end of the instrument panel. The blower motor and blower wheel can be accessed for service from the passenger compartment without removing the system housing.
The blower motor and blower motor wheel cannot be adjusted or repaired, and if faulty or damaged, they must be replaced.
The blower motor will only operate when the ignition switch is in the ON position, and the blower control switch is in any position except OFF. The blower motor circuit is protected by a fuse in the instrument panel fuse block. The blower motor speed is controlled by regulating the battery feed through the blower control switch and the blower motor resistor. The blower motor and wheel are used to control the velocity of air moving through the heater-only or heater-A/C unit housing. The blower motor controls the velocity of the air flowing through the heater-A/C housing by spinning the blower wheel within the housing at the selected speed.
BLOWER MOTOR RESISTOR
Fig.9 Blower Motor Resistor Location:
There are two different blower motor resistor blocks used on this model, one for the standard heater-only system and one for the optional heater-A/C system. The blower motor resistor is installed in a mounting hole located on the right side of the cowl plenum panel below the base of the windshield. It snaps into the mounting hole and is accessed for service from within the cowl plenum panel by removing the cowl plenum grille and screen unit.
The blower motor resistors will get hot when in use. Do not touch resistor block if the blower motor has been running. The blower motor resistor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.
Fig.10 Blower Motor Resistors:
The resistor has multiple resistor wires, each of which will reduce the current flow through the blower motor to change the blower motor speed. The blower motor switch directs the ground path for the blower motor through the correct resistor wire to obtain the selected speed.
With the blower motor switch in the lowest speed position, the ground path for the motor is applied through all of the resistor wires. Each higher speed selected with the blower motor switch applies the blower motor ground path through fewer of the resistor wires, increasing the blower motor speed. When the blower motor switch is in the highest speed position, the blower motor resistor is bypassed and the blower motor receives a direct path to ground through the blower motor switch.
REFRIGERANT
The refrigerant used in this air conditioning system is a HydroFluoroCarbon (HFC), type R-134a. Unlike R-12, which is a ChloroFluoroCarbon (CFC), R-134a refrigerant does not contain ozone-depleting chlorine. R-134a refrigerant is a non-toxic, non-flammable, clear, and colorless liquefied gas.
Even though R-134a does not contain chlorine, it must be reclaimed and recycled just like CFC-type refrigerants. This is because R-134a is a greenhouse gas and can contribute to global warming.
R-134a refrigerant is not compatible with R-12 refrigerant in an air conditioning system. Even a small amount of R-12 added to an R-134a refrigerant system will cause compressor failure, refrigerant oil sludge or poor air conditioning system performance. In addition, the PolyAlkylene Glycol (PAG) synthetic refrigerant oils used in an R-134a refrigerant system are not compatible with the mineral-based refrigerant oils used in an R-12 refrigerant system.
R-134a refrigerant system service ports, service tool couplers and refrigerant dispensing bottles have all been designed with unique fittings to ensure that an R-134a system is not accidentally contaminated with the wrong refrigerant (R-12). There are also labels posted in the engine compartment of the vehicle and on the compressor identifying to service technicians that the air conditioning system is equipped with R-134a.
REFRIGERANT OIL
The refrigerant oil used in R-134a refrigerant systems is a synthetic-based, PolyAlkylene Glycol (PAG), wax-free lubricant. Mineral-based R-12 refrigerant oils are not compatible with PAG oils, and should never be introduced to an R-134a refrigerant system.
There are different PAG oils available, and each contains a different additive package. The 10S15 and 10S17 compressors used in this vehicle is designed to use an ND-8 PAG refrigerant oil. Use only refrigerant oil of this same type to service the refrigerant system.
After performing any refrigerant recovery or recycling operation, always replenish the refrigerant system with the same amount of the recommended refrigerant oil as was removed. Too little refrigerant oil can cause compressor damage, and too much can reduce air conditioning system performance.
PAG refrigerant oil is much more hygroscopic than mineral oil, and will absorb any moisture it comes into contact with, even moisture in the air. The PAG oil container should always be kept tightly capped until it is ready to be used. After, recap the oil container immediately to prevent moisture contamination.
A/C REFRIGERANT LINES
Fig.11 A/C Refrigerant Lines - Compressor:
Fig.12 A/C Refrigerant Lines - Condenser:
Fig.13 A/C Refrigerant Lines - Accumulator/Evaporator:
The refrigerant lines and hoses, and are used to carry the refrigerant between the various air conditioning system components. A barrier hose design with a nylon tube, which is sandwiched between rubber layers, is used for the R-134a air conditioning system on this vehicle. This nylon tube helps to further contain the R-134a refrigerant, which has a smaller molecular structure than R-12 refrigerant. The ends of the refrigerant hoses are made from lightweight aluminum or steel, and commonly use braze-less fittings.
Any kinks or sharp bends in the refrigerant plumbing will reduce the capacity of the entire air conditioning system. Kinks and sharp bends reduce the flow of refrigerant in the system. A good rule for the flexible hose refrigerant lines is to keep the radius of all bends at least ten times the diameter of the hose. In addition, the flexible hose refrigerant lines should be routed so they are at least 80 millimeters (3 inches) from the exhaust manifold.
The refrigerant Tines used for this vehicle are common between the two optional engines in order to reduce complexity. The following refrigerant lines are available for service replacement on this vehicle:
- Discharge line - The discharge line is a flexible hose type line that is connected from the discharge port of the compressor to the inlet (upper fitting) of the condenser. It has no serviceable parts except the rubber O-ring seals used on the fittings at each end of the line. If the discharge line is damaged or faulty, it must be replaced.
- Liquid line - The liquid line is a flexible hose type line that is connected between the outlet (lower fitting) of the condenser and the mid-line connector block of the suction and liquid line assembly The liquid line also contains the variable orifice valve. It has no serviceable parts except the rubber O-ring seals used on the fittings at each end of the line. If the liquid line or the variable orifice valve are damaged or faulty, the liquid line unit must be replaced.
- Suction line - The suction line is a flexible hose type line that is connected between the mid-line connector block of the suction and liquid line assembly and the suction port of the compressor. It has no serviceable parts except the rubber O-ring seals used on the fittings at each end of the line. If the suction line is damaged or faulty, it must be replaced.
Fig.14 A/C Service Ports:
- Suction and liquid line assembly - The suction and liquid line assembly is a formed tubing type line assembly that includes the mid-line connector block, a connector block for the evaporator, inlet and outlet line fittings for the accumulator and both A/C service ports. The A/C service port caps, the A/C service port valve cores, the gasket used to seal the connector block at the evaporator and the rubber O-ring seals for the line fittings at the accumulator are all available for service replacement. If any other part of the suction and liquid line assembly is damaged or faulty, the assembly must be replaced.
High pressures are produced in the refrigerant system when the air conditioning compressor is operating. Extreme care must be exercised to make sure that each of the refrigerant line connections is pressure-tight and leak free. It is a good practice to inspect all flexible hose refrigerant lines at least once a year to make sure they are in good condition and properly routed.