Pre-Diagnostic Preparations

Satisfactory heater and air conditioner performance depends upon proper operation and adjustment of all operating controls and refrigeration system components. 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. Inspect the condition, routing, and installation of the temperature control cable. See the Temperature Control Cable Removal and Installation procedure for more information.
2. Inspect and adjust the serpentine drive belt. Refer to - Cooling System for the procedures.
3. Start the engine and hold the idle speed at 1,300 rpm.
4. On vehicles with air conditioning, move the temperature control knob to the extreme left (Cool) position, and set the mode control switch knob in the Bi-Level position. The outside (recirculation) air door should be open to outside air. If not OK, SEE the Vacuum System Tests.
5. Open the vehicle windows. Test the blower motor operation in all speeds. If not OK, see the diagnosis for the blower motor components. Leave the blower motor switch in the High speed position.
6. On vehicles with air conditioning, the compressor should be running and the air conditioning system in operation. If not OK, see the A/C Performance or Compressor Clutch Coil test procedures.
7. Check the mode control switch operation. The heater and air conditioner systems should respond as described in the owner's manual 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 the Vacuum System test procedures.
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.