What are the changes in high and low pressure of car air conditioning, and what are the reasons?
2 Answers
There are four changes in the high and low pressure of car air conditioning. The specific reasons for the pressure changes and the corresponding solutions are as follows: 1. Pressure gauge detects car air conditioning: high pressure is low, low pressure is high. Reason: Compressor failure. Solution: Replace the compressor. 2. Pressure gauge detects car air conditioning: low pressure is low, high pressure is low. Reason: Insufficient refrigerant, which is a common phenomenon. Solution: After inspection, refrigerant can be directly refilled. 3. Pressure gauge detects car air conditioning: low pressure is high, high pressure is high. Reason: Expansion valve stuck open fault. Solution: Replace the expansion valve. 4. Pressure gauge detects car air conditioning: low pressure is in vacuum (pointer below 0 scale), high pressure is low. Reason: Expansion valve stuck closed fault. Solution: Replace the expansion valve.
Driving in summer with the AC not cooling properly can be quite concerning due to fluctuating high and low pressures. The high pressure typically ranges between 150 to 200 psi. If it spikes above 250 psi, it’s likely due to poor condenser cooling, a non-functioning fan, or debris clogging the radiator grille—especially more common in high external temperatures. The low pressure normally sits at 30 to 40 psi. If it drops too low, say to 20 psi, it’s usually caused by refrigerant leakage or insufficient levels. Conversely, if it rises too high, like 45 psi, it could indicate a stuck expansion valve or overcharged refrigerant. These fluctuations reduce cooling efficiency, forcing the compressor to work harder, which wastes fuel, damages components, and may even lead to a breakdown. Last year, while helping a neighbor fix their car, I found extremely high pressure caused by moss growing on the condenser fins. After cleaning, the pressure normalized, and the AC blew cold air again. Regularly monitoring with a pressure gauge can prevent major issues.
