Automotive AC – Heat Load Testing

Performing a heat load test on an AC system is an effective method of measuring the system’s performance. It is important to remember that this test in only valid when the ambient temperature is above 75°F. Performing the test at cooler temperatures will produce faulty results.

Setup for the Heat Load Test

1. Start the vehicle and let the engine reach normal operating temperature.
2. Turn the AC to maximum and the blower to high speed.
3. Open the doors and windows on the vehicle and let it be exposed to the sunlight if possible.

The engine temperature needs to be raised to normal operating range to prepare for running the heat load

The HVAC controls need to be set to the coldest setting with the blower speed set to the highest setting during the heat load

The heat load test is the most accurate when the vehicle is exposed to sunlight and the windows and doors are open on the

The temperature of the line entering the condenser needs to be checked with some type of temperature-sensing’

The temperature of the line exiting the condenser needs to be measured. The temperature needs to be measured at approximately the same distance away from the condenser as the previous

4. Let the engine run at idle speed.
5. Measure the inlet line and the exit line at the condenser.
6. Measure the ambient temperature as well as the duct temperature.

Expected Results

1. The duct temperature should be at least 30 degrees cooler than the ambient temperature.
2. The condenser outlet temperature should be between 20 and 50 degrees cooler than the inlet temperature.

The ambient temperature needs to be measured and documented. This test is only valid with ambient temperatures above

The duct temperature at the center duct needs to be measured and documented during the heat load test. The temperature at the center duct will usually not be as cold as it is during a performance test because this test is done at idle and with the doors

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