Section II. System Response Diagnosis

Vacuum controlled ATC malfunctions can be divided into three basic groups:

1. Improper discharge temperature control
2. Improper blower speed control
3. Improper system inlet control

The predominant causes of failures in the system are vacuum leaks (anywhere in the vehicle), cable adjustments, and aspirator hose connections. The following is a detailed checkout procedure to fully analyze the response of the ATC system and isolate the inoperative component.

Response Checkout Procedure

Test Equipment:

Vacuum gage 0-30 in.hg. Voltmeter 0-15 V D.C. Continuity Tester

Test Conditions:

Engine Warm (10 minutes running) Engine above 1200 RPM Vehicle Interior 75 +/- 5~F

STEP 1 - Install vacuum gauge with tee in line at ATC servo (large clear line behind glove box).

STEP 2 - Connect voltmeter across blower motor leads.

VIEW 1 - BLOWER TROUBLESHOOTING:

STEP 3 - To check the response of the system, set the function control lever in the A/C position, then with engine warm and interior at 75 +/- 5~F, slowly move temperature lever from 65 to 85. Allow sufficient time for the system to settle out at each setting. Then move lever back to 65. Refer to View 2 and the vacuum/blower and temperature response test for normal results.

VACUUM/BLOWER AND TEMPERATURE RESPONSE TEST

TEST STEP TEST RESULT CONCLUSION ACTION TO TAKE

A0. Vacuum Response Vacuum low at 85, high Normal Go to A1
at 65

No vacuum change Incorrect ^ Check vacuum supply to
Vacuum sensor
Response

^ Check temperature cable

attachment and movement

VIEW 1 - BLOWER TROUBLESHOOTING:

A1. Blower Response Should change from Normal Go to A2
high to lower speeds
and back to high Incorrect See View 1
A2. Temperature Response Should be warm at 85, Normal Recheck basic refrigerant
cool at 65 and heating systems

Incorrect See Section III., ATC
Temperature Control Diagnosis