Should Refrigerant Be Added from the Low or High Pressure Side in a Car?
3 Answers
Refrigerant can be added from either the low or high pressure side in a car. The steps for adding refrigerant are: 1. Evacuate the system, close the manual valves on the manifold gauge, and connect one end of the middle hose to the refrigerant canister injection valve; 2. Open the refrigerant canister valve, loosen the nut at one end of the manifold gauge hose to allow gas to escape; 3. Tighten the nut, open the high and low pressure side manual valves fully, invert the refrigerant canister, and inject the specified amount of liquid refrigerant from the high and low pressure sides. Signs of refrigerant leakage in a car include: 1. The car air conditioning not cooling; 2. The compressor not working; 3. Oil stains leaking from the compressor.
When I first learned auto repair, I was also curious about this. You add it from the low-pressure side because the low-pressure pipe is connected to the compressor's suction port, where the pressure is lower and easier to operate. The high-pressure pipe has too much pressure, and forcibly opening the valve can cause refrigerant to spray and injure people. Before adding refrigerant, you need to start the air conditioning and set it to maximum cooling to let the compressor run. Wait until the low-pressure gauge stabilizes before slowly adding the refrigerant—don’t rush. If you notice that the temperature difference between the high and low-pressure pipes is small or the air conditioning isn’t as cool as before, it might be time to consider adding refrigerant. However, this job is best left to professional technicians. Doing it yourself can easily damage the AC system and waste refrigerant, leading to higher repair costs.
Last time my car's air conditioning wasn't cooling, the repair shop said it was low on refrigerant. The technician opened the hood, located the low-pressure charging port, and performed the operation very skillfully. He explained the difference between high and low pressure: the low-pressure pipe is thinner and usually labeled L, while the high-pressure pipe is thicker and labeled H. Refrigerant must be added from the low-pressure side because the high-pressure side has too much pressure, and forcibly opening the valve could injure someone's hand. During the operation, a pressure gauge must also be used to monitor the values, as adding too much refrigerant can overload and damage the compressor. So, if your air conditioning's cooling performance changes, don't try to fix it yourself—it's more reliable to go to a professional shop.
