OPERATION - HEATER AND AIR CONDITIONER
Both the manual temperature control (MTC) heating-A/C system and the heater-only system are blend-air type systems. In a blend-air system, a blend-air door controls the amount of conditioned air that is allowed to flow through, or around, the heater core. The temperature control determines the discharge air temperature by operating the blend door cable, which moves the blend-air door. This design allows almost immediate control of output air temperature.
Scheme 3
Note. Typical blend-air type HVAC system shown in illustration.
The heating-A/C system pulls outside (ambient) air through the fresh air intake (4) located at the cowl panel at the base of the windshield and into the air inlet housing above the heating, ventilation and air conditioning (HVAC) housing. On models equipped with A/C, the air passes through the A/C evaporator (7). Air flow is then directed either through or around the heater core (2). This is done by adjusting the position of the blend-air door (3) with the temperature control located on the A/C-heater control in the instrument panel. Air flow is then directed out the floor outlet (8), instrument panel outlet (10) or the defroster outlet (1) in various combinations by adjusting the position of the mode-air doors (9 and 11) using the mode control located on the A/C-heater control. The mode control uses a control cable to operate the mode-air doors.
The velocity of the air flow out of the outlets can be adjusted with the blower speed control located on the A/C-heater control.
The fresh air intake can be shut off by pressing the Recirculation button on the A/C-heater control. This will operate the electrically actuated recirculation-air door (5), which closes off the fresh air intake. With the fresh air intake closed, the conditioned air within the vehicle is pulled back into the HVAC housing through the recirculation air intake (6) located within the passenger compartment.
The A/C compressor can be engaged by pressing the A/C (snowflake) button on the A/C-heater control. It will automatically engage when the mode control is set in any Mix to Defrost position. This will remove heat and humidity from the air before it is directed through or around the heater core. The mode control on the A/C-heater control is used to direct the conditioned air to the selected system outlets.
The front and rear floor outlets receive airflow from the HVAC housing through the front and rear floor ducts. The front floor outlets are integral to the molded plastic front floor ducts, which are secured to each side of the HVAC housing. Two molded plastic rear seat ducts are attached to the two molded plastic rear floor ducts, which are secured to the rear of the HVAC housing. The rear seat ducts direct airflow beneath the carpet to the outlets located near the front of each rear seat foot well. None of the floor outlets can be adjusted.
The panel outlets receive airflow from the HVAC housing through the center air distribution duct and molded plastic panel outlet ducts. The airflow from each of the panel outlets is adjustable. A thumbwheel located at the bottom of each panel outlet grille is used 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 defroster outlet receives airflow from the HVAC housing through the molded plastic defroster duct, which is secured to the top of the instrument panel. The airflow from the defroster outlet is directed by fixed vanes in the defroster outlet grille and cannot be adjusted.
The side window demister outlets receive airflow from the HVAC housing through the defroster duct and molded plastic demister ducts. 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 cover and direct air from the HVAC housing through the outlets on the top corners of the instrument panel. The demisters operate when the mode control is set in any Floor to Defrost position.
OPERATION
Possible causes of an inoperative blower motor include
- Open fuse
- Inoperative blower motor resistor
- Inoperative blower motor switch
- Inoperative blower motor
- Inoperative blower motor circuit wiring or wire harness connectors
The variable A/C orifice tube provides improved A/C system cooling during city driving and when under heavy loads by controlling refrigerant flow through the two parallel flow paths integral to the orifice tube. Under normal loads, the refrigerant flows through the inlet filter screen, the fixed and variable ports and both metering orifices. As the load on the A/C system increases, the temperature of the refrigerant leaving the A/C condenser increases, which causes the bi-metal coil to expand and restrict the flow of refrigerant through the variable port of the tube. Restricting the flow of refrigerant through the variable port and its orifice provides a greater pressure differential between the high and low pressure sides of the A/C system, resulting in colder refrigerant vapor traveling through the A/C evaporator to help remove the heat from the conditioned air flowing into the passenger compartment.
The A/C orifice tube is not serviceable and the A/C liquid line must be replaced if the orifice tube is found inoperative. See DESCRIPTION .
Scheme 4
Condensation that accumulates within the HVAC housing is drained through a port located at the bottom of the HVAC housing (1). A rubber condensation drain tube (2) is installed onto the drain port and protrudes through a rubber grommet (3) in the left side floor panel (4) to ensure that any condensate completely drains out of the HVAC housing and to the ground.
Note. The condensation drain tube must be kept open to prevent water from collecting in the bottom of the HVAC housing.
The drain tube is designed to keep contaminants from entering the HVAC 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 condensation drainage below the vehicle in warm weather.
If the condensation drain tube is damaged or missing, it must be replaced.