Generally, it is recommended to evacuate a car air conditioning system for about 30 minutes. If the system is too dirty or the pipelines have been exposed to the atmosphere for too long due to rupture, it is advisable to evacuate for one hour, preferably during warmer weather. In summary, the longer the vacuum evacuation process, the more thoroughly moisture is removed from the system as the pressure decreases, which is more beneficial for the air conditioning system. The steps for evacuating a car air conditioning system are as follows: 1. Connect the refrigeration system, manifold gauge set, and vacuum pump properly. The high and low service valves on the compressor should be slightly open, while the high and low pressure manual valves on the manifold gauge set should be closed. Remove the protective covers from the vacuum pump's suction and exhaust ports, and connect the middle hose of the manifold gauge set to the vacuum pump's inlet and outlet. 2. Open the high and low pressure manual valves on the manifold gauge set, start the vacuum pump, and observe the low-pressure gauge needle, which should display a vacuum reading. 3. After 5 minutes of operation, the low-pressure gauge should reach 33.6 kPa (absolute pressure), and the high-pressure gauge needle should drop below the zero mark. If the high-pressure gauge needle does not drop below zero, it indicates a blockage in the system. Stop the process, address the issue, and then resume evacuation. 4. After the vacuum pump has operated for 15 minutes, observe the pressure gauge. If there are no leaks in the system, the low-pressure reading should reach an absolute pressure of 13.28-20.05 kPa. 5. If this value is not achieved, close the low-pressure manual valve and observe the low-pressure gauge needle. If the needle rises, it indicates a vacuum loss. Inspect for leaks, perform necessary repairs, and then continue the evacuation process. This step is essentially the vacuum leak test method. 6. The total evacuation time should not be less than 30 minutes. After this, close the low-pressure manual valve, and you can proceed to charge the system with refrigerant.
