Why is the low pressure of the car air conditioner high while the high pressure is normal?
3 Answers
When the car air conditioner exhibits low low pressure and normal high pressure, it is highly likely due to a malfunction or damage of the air conditioner expansion valve. If the ambient temperature around the vehicle is high, the high pressure may reach approximately 2.5-2.8 MPa, but it generally does not exceed 3.1 MPa; otherwise, the pressure protection switch will be triggered. Additional information: The solution for high low pressure and normal high pressure in a car air conditioner is quite simple. You just need to remove the air conditioner expansion valve and check if it is functioning properly. If it is indeed faulty or damaged, simply replace it. However, since the expansion valve of the car air conditioning system is located on the firewall side of the vehicle, disassembly is quite inconvenient. Additionally, temporary recovery of the air conditioner refrigerant is required, making the task labor-intensive. Therefore, it is best to have it handled at a 4S shop.
I've seen quite a few cases where the AC low pressure is high while the high pressure remains normal. I think it's very likely due to overcharged refrigerant - when there's too much refrigerant in the system that can't be properly compressed, the low pressure rises while high pressure stays normal, resulting in poor AC performance. Another possible cause is a stuck expansion valve that fails to regulate properly, unable to block the high-pressure side while only affecting the low pressure, making the system malfunction. Compressor issues like worn impellers failing to draw in refrigerant can also cause this. Immediate action is needed, otherwise prolonged operation will accelerate compressor wear until complete failure - imagine suffering hot air instead of cooling during summer highway driving, which is both unbearable and dangerous. I recommend first using pressure gauges to measure exact values and checking the service port window color. If the refrigerant appears dark, visit a repair shop to have some discharged - never attempt this yourself. Also, regularly clean the condenser to prevent clogging as preventive maintenance, which counts as routine care that can save you lots of trouble.
As an experienced driver who has been on the road for years, I once encountered the issue of high low pressure but normal high pressure in the AC system, which left the car unbearably hot like a steamer. A mechanic friend of mine checked it and said the usual culprits are either too much refrigerant or a failing expansion valve. Basically, if the airflow on the low-pressure side can't be controlled properly, the pressure goes up. Even though the high pressure is normal, the system is out of balance and performs poorly. After releasing some refrigerant and fixing the expansion valve, everything went back to normal. I learned my lesson: regularly check the refrigerant level and avoid overfilling it. Also, pay attention to the air vent temperature before turning on the AC in summer. Ignoring such minor issues can overwork the compressor, leading to costly replacements and even compromising driving safety, especially on long trips. Now, I make it a point to have the AC system inspected during annual maintenance, keeping the condenser clean to prevent dust buildup and low-pressure issues. It’s a hassle-free and cost-effective approach.
