Testing automotive AC can be tackled in the driveway by a DIY car mechanic with some experience wearing comfortable safety glasses. Performance testing the system is a good place to start.
Performance testing provides a measurement of air-conditioning system operation and efficiency. It is recommended that a manifold pressure gauge be used to determine both the high and low pressures in the automotive AC system.
These manifold gauge sets have really come down in price over the last few years. Although professional grade sets can cost well over $100 a good DIY set can be had for fewer than 50.
This could be considered a good investment that will return big rewards over time on several different vehicles.
Automotive AC pressure readings
You can use a basic rule of thumb that the low side readings should be around 35 psi. Also the high side should read anywhere from 150 to 200 psi. This is just a generalization and these readings will again be determined by the amount of Freon in the system and the outside temperature during testing.
This can be further confirmed with a check of the output duct temperature. You can use a thermometer inserted in the center duct to determine the discharge temperature into the passenger compartment. They do make specialized thermometers that will clip onto the vent grille and provide an accurate reading.
A good tip for obtaining the most real world temperature output. For the best results place a high speed fan in front of the radiator grille to simulate road operation and provide sufficient airflow across the condenser. For the most accurate reading place your thermometer in the center duct and reduce your blower setting to either low or low 2. Placing the blower on a higher setting actually rushes the air through the evaporator and can increase output temperatures.
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