How To Isolate The Problem

To diagnose an air conditioner problem in the shortest time and with the least effort, it is essential to follow a logical service procedure. Time spend in conducting system functional performance test and analyzing the defect in order to isolate it to a specific control function area will be repaid in reduced repair time. A recommended diagnosis procedure follows:

Fig 1: Automatic Climate Control Wiring Diagram

Courtesy of GENERAL MOTORS COMPANY

1. Attempt to get an accurate, detailed description of the system malfunction. This will help locate the problem area as testing procedures are followed.
2. Confirm system defect by operating system with engine at normal operating temperature and engine RPM at 1000 or higher, then perform the following System Functional Test in exact order shown. Set selector lever and temperature dial as indicated, then observe system for proper response;
3. During above sequence be sure to note the following:
   1. Check to assure that air delivery is not coming from both A/C outlets and heater outlets when only one mode is indicated. A split air delivery is indicative of a vacuum leak.
   2. Note whether program events (air delivery mode change, blower speed change, recirc air change, etc.) occur without change in discharge air temperature. This would indicate programmer is operating without moving temperature air door. Check air mix door link to programmer connection.
   3. If neither program events nor discharge air temperature change, a faulty vacuum or electrical signal to programmer or a programmer malfunction is indicated.
   4. Failure of a specific vacuum operated door function could indicate a vacuum disconnect of the vacuum diaphragm at that door.
4. Perform easiest checks first. A simple visual inspection of easily accessibly underhood and instrument panel components will possibly reveal a defect on the spot. It may be necessary to remove lower instrument panel cover to inspect control head.
5. Based on information gained during the preceding functional test, try to relate the problem to one of the following areas: temperature control problems, blower control problems, auxiliary vacuum problems, or refrigeration system problems.
6. Once a problem has been isolated to a specific area, refer to that particular diagnosis section on the following pages.
7. After problem has been properly diagnosed and repaired, it is important to perform the Functional Test again to insure proper operation of the entire system.