Satisfactory heater and air conditioner performance depends upon proper operation and adjustment of all operating controls and refrigeration system components. For circuit descriptions and diagrams, refer to 8W-42 - Air Conditioning/Heater in Group 8W - Wiring Diagrams. These inspections, tests, and adjustments should be used to locate the cause of a malfunction.
Operation must be tested as described in the following sequence: (1) Move the temperature control knob quickly to the full hot and the full cold positions. There should be a distinct sound of the blend-air door hitting its stops within the heater-A/C housing at the end of knob travel in each direction, with no spring-back of the knob. If not OK, inspect the condition, routing, installation and adjustment of the temperature control cable. See Temperature Control Cable in the Removal and Installation section and in the Adjustments section of this group for more information.
(2) Inspect and adjust the serpentine drive belt.
Refer to Group 7 - Cooling System for the procedures.
(3) Start the engine and hold the idle speed at 1,300 rpm.
(4) On vehicles with air conditioning, turn the temperature control knob to the extreme counterclockwise (Cool) position, and set the mode control switch knob in the Bi-Level (A/C) position. The outside (recirculation) air door should be open to outside air. If not OK, see Vacuum System in the Diagnosis and Testing section of this group.
(5) Open the vehicle windows. Test the blower motor operation in all speeds. If not OK, see Blower Motor in the Diagnosis and Testing section of this group. Leave the blower motor switch knob in the highest speed position.
(6) On vehicles with air conditioning, the compressor should be running and the air conditioning system in operation unless the ambient air temperature is below about -1 C (30 F). If not OK, see A/C Performance in the Diagnosis and Testing section of this group.
(7) Check the mode control switch operation. The heater and air conditioner systems should respond as described in the owner's manual in the vehicle glove box to each mode selected. Reduce the engine speed to normal idle. The vacuum will be high at low idle and the vacuum actuators should respond quickly. If not OK, see Vacuum System in the Diagnosis and Testing section of this group.
(8) If the vacuum tests, and the electrical component and circuit tests reveal no problems, disassemble the heater-A/C housing to inspect for mechanical misalignment or binding of the mode doors.