Isolating The Problem

To diagnose a problem in the least amount of time and to eliminate guesswork, follow a logical sequence of quick checks as outlined below:

1. Sit in car with windows and doors closed, and engine running at 1000 RPM or higher, then perform the "FUNCTIONAL TEST " as shown in this article.
2. During the Functional Test, ensure that air delivery is not coming from both A/C and heater outlets when only one mode is indicated. A split air delivery is indicative of a vacuum leak.
3. Also note whether program events (air delivery mode change, blower speed change, etc.) occur without change in discharge air temperature. This would indicate the programmer is operating without moving temperature air door. Check the air mix door link-to-programmer connection.
4. If neither the programmer events or discharge air temperature change, an incorrect vacuum or electrical signal to the programmer is indicated; and possibly a programmer malfunction.
5. Malfunction of a specific vacuum-operated door function could indicate a vacuum disconnect of the vacuum diaphragm at that door.
6. A visual inspection is an easy method of checking for disconnects or malfunctions. Once the problem has been generalized, try to relate it to one of the following areas: temperature control problem; blower control problem; auxiliary vacuum problem; refrigeration system problem. Then refer to the appropriate diagnosis chart in this article.
7. After the problem has been diagnosed and repaired, perform another FUNCTIONAL TEST  to ensure proper operation.