Does a car air conditioning compressor need refrigerant oil?
2 Answers
When replacing a car air conditioning compressor, it is necessary to add refrigerant oil. There are three main methods for adding compressor refrigerant oil: direct addition, addition from the high-pressure side, and addition from the low-pressure side. The method can be chosen flexibly based on the specific situation. If adding directly to the compressor, an oil return operation should be performed first. This involves running the compressor at idle speed with the control system set to the coldest temperature and highest fan speed for 20-30 minutes to allow the oil to return to the compressor. Then, turn off the engine, release the refrigerant, remove the compressor from the vehicle, drain the old oil, and directly add or replenish new oil. For adding from the high-pressure side, evacuate to 98kPa, close the high-pressure side manual valve, and close the service valve on the compressor. Remove the high-pressure side hose from the pressure gauge head and insert it into the refrigerant oil. Open the service valve, and the refrigerant oil will be immediately drawn into the system. Close the service valve quickly as the oil is almost fully drawn to avoid sucking in air. Then, reattach the high-pressure hose to the gauge head, open the high-pressure side manual valve, continue evacuating, and then add refrigerant. During this process, neither the engine nor the vacuum pump should be running. For adding from the low-pressure side, evacuate to 98kPa, then close the low-pressure side manual valve while the vacuum pump continues to evacuate. Keep the high-pressure side manual valve open, remove the low-pressure side hose from the pressure gauge head, insert it into the refrigerant oil to draw the oil, and reattach the hose once the oil is fully drawn. Open the low-pressure side manual valve, continue evacuating, and then proceed with adding refrigerant. Note that too much refrigerant oil can impair cooling performance, while too little can damage the compressor. Always add the specified amount according to the vehicle's requirements.
I remember last summer when the air conditioning suddenly stopped cooling while driving, accompanied by a strange buzzing noise. After taking it to the repair shop, I learned it was due to insufficient refrigerant oil. The mechanic explained that the compressor internals require adequate lubricating oil to lubricate the pistons and seals, otherwise excessive friction can cause wear. Under normal circumstances, the compressor is sealed, and refrigerant oil doesn’t deplete—it only needs replenishing if there’s a system leak or major repairs, such as after replacing the compressor or refrigerant. That time, it cost me a few hundred dollars to fix. Now, I regularly check if the AC operates smoothly and promptly investigate any unusual noises. The type of refrigerant oil must match the original vehicle specifications—common types include PAG oil or ester-based oil—as using the wrong one could damage the entire system. In short, if you encounter AC issues, don’t tough it out; it’s safer to have a reliable repair shop diagnose the problem.
