System Check

SYSTEM CHECK

Test conditions:

^ Engine warm and above 1200 rpm
^ Vehicle interior 24°C ±3°C (75°F ±5°F)

1. Check air distribution for proper operation in each function. If fault is found, it must be corrected before proceeding to the ATC checkout.

2. Set function selector to VENT position. Check blower operation in low and high. If OK, move selector to AUTO. If blower does not operate properly in all positions, correct inoperative component and proceed. Refer to Blower Speed Controller Diagnosis.

3. Cycle temperature lever from 65°-85°F and observe blower speed change and discharge temperature change. The chart in Fig. 27 shows the relationship of these functions.

4. Move the temperature lever back to 65°F and observe the blower and temperature outputs.

5. With the temperature lever still at 65°F, move the function lever to NORM A/C. The outside air/ recirc door should open and the A/C compressor clutch should engage to produce colder discharge temperatures.

6. Move the temperature lever to 72°-75°F Blower speed should reduce down to low or medium low and the discharge temperature rise to a more moderate level.

Fig. 27 ATC Performance Check At 75 Degrees +/- 5 Degrees - Interior Temperature:

Component Identification

ATC malfunctions can be divided into three groups:

- Improper discharge temperature control
- Improper blower speed control
- Improper system air discharge control

The most common cause of failures in the system are vacuum leaks (these leaks can be anywhere in the vehicle), and aspirator hose connections. The following is a detailed checkout procedure to fully analyze the ATC system and isolate the inoperative components.