Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Isolating The Problem: Notes
To diagnose an automatic air conditioning system problem in the shortest time, and with least effort, it is essential to follow a logical service procedure. Time spent in conducting a 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. Perform trouble shooting and diagnosis in the order indicated in this article.
- Attempt to get an accurate, detailed description of system malfunction from customer.
- Confirm system defect by performing Functional Performance Test and noting system responses. During this test, also note the following points:
- Insure that air delivery is not coming from both A/C and heater outlets when only one mode is indicated. A split air delivery shows a vacuum leak.
- Note whether changes in system function (air delivery mode, blower speed changes, etc.) occur without changes in discharge air temperature. If no change in temperature, programmer is operating without moving temperature air door. Check air-mix door link-to-programmer connection.
- If neither the events indicated in test chart or discharge air temperature change, a faulty vacuum or electrical signal to programmer or a defective programmer is indicated.
- Failure of a specific vacuum-operated door could indicate vacuum disconnect at that door or mechanical problem.
- Perform easiest checks first. Make visual inspection of all components for any defect. It may be necessary to remove lower instrument panel cover to inspect control head.
- Based on information gained in these proceeding steps, try to relate the problem to one of the following areas: temperature control problem, blower control problem, auxiliary vacuum problem, or refrigeration system problem. When problem is isolated to one of these areas, refer to appropriate information in this article for further trouble shooting and diagnosis.
- After problem has been properly diagnosed and repaired, it is important to perform a FUNCTIONAL PERFORMANCE TEST again to insure proper operation.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.