Should refrigerant be added from the high-pressure or low-pressure side in a car?
2 Answers
Generally, it is added from the low-pressure side, primarily because the system uses vacuum extraction, and the high-pressure side retains an interface. Therefore, it is typically added from the low-pressure side. When adding refrigerant, the air conditioning should be turned on, as this makes it easier to determine whether enough has been added and allows the refrigerant to enter the system more efficiently due to the pressure difference. Refrigerant, also known as coolant, is usually replenished every 5-8 years. The reasons why a car's air conditioning system may require frequent refrigerant top-ups include: Condenser and Radiator: The cooling efficiency of the condenser and radiator also affects the performance of the air conditioning system. Prolonged lack of cleaning can lead to the condenser and radiator being covered with dust and debris. Expansion Valve Quality: The expansion valve is a critical component in the refrigeration system, usually installed between the liquid receiver and the evaporator. A poor-quality expansion valve can prevent the refrigerant from functioning as intended. Refrigerant Usage: During the refrigerant charging process, the amount must be neither too much nor too little. Too little results in insufficient pressure in the air conditioning pipes, while too much leads to excessive pressure. In both cases, the air conditioning system will fail to operate and cool properly. Refrigerant Quality and Purity: The quality and purity of the refrigerant play a crucial role in the vehicle's air conditioning system. Typically, low-quality refrigerant can lead to inefficient operation of the air conditioning system.
I've been driving for over ten years and have added refrigerant several times myself, always from the low-pressure side. Why? Because the high-pressure side has too much pressure. If you force it, the pipes might burst or the refrigerant could spray out, which is very dangerous. The low-pressure side is usually marked with an 'L' or a blue cap on the AC line, with lower pressure, making it easier to control the injection amount. Last summer, before checking the AC, I found the cooling was insufficient, so I bought a refill tool and connected it to the low-pressure port. Slowly adding the refrigerant restored the system's cooling. Don't forget to turn off the engine first and use a pressure gauge to check that the pressure is within the normal range before starting, to avoid overfilling and damaging the compressor. In fact, the car maintenance manual also emphasizes this point—beginners should start with the low-pressure side. Once you get used to it, it's both safe and cost-effective.
