Section I. General Checkout Procedure

Test Condition: Engine warm and operating above 1200 RPM Vehicle interior 75 +/- 5~F

STEP 1 - Check air distribution for proper operation in each Function Selector lever position. Airflow should be directed as follows:

OFF POSITION - No airflow VENT POSITION - Airflow out panel registers only PANEL POSITION - Airflow out panel registers only HI-LO POSITION - Airflow out panel registers and floor duct
FLOOR POSITION - Airflow out floor duct with a slight amount out the defroster
MIX POSITION - Airflow split between floor duct and defroster outlets
DEFROST POSITION - Airflow out the defroster outlets

If the results are not as described above, the most likely cause of concern is vacuum leaks. These vacuum leaks may occur at any point in the system. To locate a vacuum leak, refer to the following tests located in Shop Manual, Section 36-70:

^ Hissing ATC vacuum system or control assembly selector valve test.
^ All function selector valve positions leak test.
^ Some temperature control level positions leak test.
^ ATC system airflow schematic and vacuum control chart.

VIEW 1 - BLOWER TROUBLESHOOTING:

STEP 2 - To check manual blower operation, set the function selector lever to the vent position. Check the blower operation in Low, Medium, and High speeds. If the blower operation is O.K., move the blower selector lever to the Auto position and proceed to Step 3. If the blower does not operate properly in all manual speeds, refer to (View 1) blower troubleshooting. Correct the inoperative component and proceed.
STEP 3 -To check for proper Auto blower speeds and temperature lever relationships, set the function selector lever to vent and the blower selector lever to Auto. Next, slowly cycle the temperature lever setting from 65 to 85, then slowly returning back to 65.

Typical Results

^ When operating at the 65 setting, the auto blower speed should be high and the discharge temperature should be equivalent to outside (ambient) air.
^ When the temperature lever is set at 65 or 85, the autoblower should be at the highest speed. As the lever is moved the blower will shift down through medium high and medium low to the low speed and then back up to the highest speed at the opposite end.
^ The discharge temperature should be at or near ambient temperature at the 65 setting and increase to a hot discharge at the 85 setting.

VIEW 2 - ATC PERFORMANCE CHECK AT 75~ +/- 5~F INTERIOR TEMPERATURE:

^ When returning back to the 65 setting, the reverse sequence of blower speeds and discharge temperatures should occur, View 2 shows the relationship of these outputs as the temperature lever is moved.

VIEW 1 - BLOWER TROUBLESHOOTING:

If the proper relationships are not obtained, refer to (View 1) for blower troubleshooting and Section II for temperature response.
STEP 4 - Check A/C compressor clutch operation and proper Outside/Recirc door position. This may be accomplished by setting the temperature selector lever at 65 and by moving the function selector lever from the Vent position to the Panel position, Typical Results

^ When moving the function selector lever from Vent to Panel, listen for A/C compressor clutch engagement while visually observing, through the glove box, the Outside/Recirc door movement to the Recirc position.
^ When in the Recirc position, the Outside/Recirc door will be positioned to allow clear view of the blower motor wheel and the noise of the blower operation will increase.
^ In addition to listening for A/C compressor clutch engagement, feel for cooler register discharge air temperatures to verify A/C compressor clutch engagement.

Service Procedure

If the A/C compressor clutch does not engage, refer to the ATC electrical wiring diagram located in Shop Manual, Section 36-70 or the respective E.V.T.M These diagrams show the clutch circuit to locate problem areas.

The most likely cause of the Outside/Recirc door not operating properly is vacuum leakage. This may occur internally in the Outside/Recirc door vacuum motor, in the vacuum line leading to the vacuum motor, at the ATC servo, or at the vacuum selector valve on the control assembly.

To check the vacuum motor, apply a vacuum source (12 in.-15 in.) directly to the vacuum motor and observe that the vacuum level is maintained. If not, replace vacuum motor. To check the vacuum line, pinch off sections of the line and apply a vacuum source (12 in.-15 in.) and listen for leaks. Replace lines as necessary. Refer to the ATC vacuum control chart located in Shop Manual, Section 36-70.