Why does the car air conditioning high pressure fluctuate?
3 Answers
Fluctuations in the car air conditioning high pressure gauge are generally caused by internal issues in the compressor, often due to one-way valve flaps, hydraulic shock, or rapid refrigerant charging. Replacement is usually required to resolve the issue. Another possible cause is unstable high-pressure output from the compressor. You can use an air conditioning pressure gauge to check if the high-pressure gauge is oscillating—if it is, the compressor may be faulty. Below is additional information: 1. Air compressor: The car air conditioning system uses an air compressor to regulate its start-stop state. By adjusting the pressure in the air storage tank, the compressor can shut down for rest, which helps maintain the machine. 2. Working principle: The motor directly drives the compressor, causing the crankshaft to rotate, which moves the connecting rod and piston in a reciprocating motion, altering the cylinder volume. Due to pressure changes inside the cylinder, air enters through the intake valve after passing through the air filter (silencer). During the compression stroke, as the cylinder volume decreases, compressed air exits through the exhaust valve, travels through the exhaust pipe, and enters the air storage tank via the one-way valve (check valve). When the exhaust pressure reaches the rated pressure of 0.7MPa, the pressure switch controls the system to shut down automatically. When the air storage tank pressure drops to 0.5–0.6MPa, the pressure switch automatically restarts the system.
Having worked on cars for many years, I often encounter issues with the car's AC high pressure fluctuating, which is usually caused by insufficient refrigerant or air mixed into the system leading to unstable pressure. If the compressor is worn or the bearings are loose, it can produce abnormal noises, causing the high pressure to fluctuate. A clogged expansion valve is even more troublesome, as it restricts refrigerant flow, making the system prone to repeated fluctuations when temperatures rise. During inspection, first use a pressure gauge to measure the high and low pressure sides; normal fluctuations should be between 25-35 PSI. If it exceeds this range significantly, be cautious. Leaks in the piping are also a hidden danger, with oily residue at connections being a clear sign. Don’t delay—get it checked at a professional shop promptly to avoid compressor burnout or complete system leakage, as the cost will be much higher than regular maintenance.
My car often has AC issues. Last time, the high pressure fluctuation caused me to break down in the scorching heat. It turned out some refrigerant had leaked, causing erratic pressure jumps upon startup, severely affecting airflow. For a quick check, pop the hood: listen for abnormal or irregular compressor sounds; inspect if the condenser is dirty or clogged—cleaning it might help. Overloading during hot weather worsens it. During maintenance, avoid overfilling refrigerant—stick to the manufacturer’s recommended level. Addressing it early prevents minor issues from escalating, saving money and hassle.
