What Causes High Low Pressure and Low High Pressure in Car Air Conditioning?
4 Answers
High low pressure and low high pressure in car air conditioning may be caused by a malfunction in the compressor or expansion valve. Under normal circumstances, the high-pressure side of a car air conditioning system should be around 1.5-2.0 MPa, while the low-pressure side should be around 0.15-0.35 MPa. If the pressure in the car air conditioning system is abnormal, it indicates a problem with the system, and it should be inspected and repaired at a service center. More relevant information is as follows: 1. Car Air Conditioning Structure: A car air conditioning system generally consists of components such as the compressor, electronically controlled clutch, condenser, evaporator, expansion valve, receiver-drier, piping, condenser fan, vacuum solenoid valve, idle speed controller, and control system. 2. Car Compressor Range: Under normal conditions, when the compressor operates at 1500-2000 rpm, the high pressure should be around 1.5-2.0 MPa, and the low pressure should be around 0.15-0.35 MPa. If the ambient temperature around the vehicle is high, the high pressure may reach around 2.5-2.8 MPa, but it generally should not exceed 3.1 MPa.
I've been driving for over 20 years and encountered many issues with AC low/high pressure. In the AC system, refrigerant flow is controlled by the expansion valve. If this valve opens too wide or fails, the low pressure gets too high. When the compressor has internal wear and poor compression efficiency, the high pressure won't rise properly. Sometimes mechanics overcharge refrigerant or air enters the system, causing similar symptoms. I remember once during a summer road trip when the AC suddenly weakened - pressure gauge testing revealed an expansion valve issue that was fixed with replacement. Always recommend professional diagnostic equipment at certified shops rather than DIY attempts that could damage the system.
When I was an apprentice at the auto repair shop, my master told me there are three main reasons for high low pressure and low high pressure in the AC system. A stuck-open expansion valve causes excessive refrigerant flow, naturally raising the low pressure. Worn internal components in the compressor prevent effective pressurization, resulting in low high pressure. Another reason is overcharged refrigerant or air mixed into the system, affecting pressure balance. Last week, a customer's car had these symptoms, and we found worn piston rings in the compressor. After replacement, the pressure returned to normal. Note that abnormal pressure leads to poor cooling performance and increased fuel consumption.
As a car enthusiast, I've studied the principles of air conditioning systems. High low pressure and low high pressure commonly indicate abnormal refrigerant flow, primarily due to an over-opened or failed expansion valve allowing excessive refrigerant into the evaporator. Compressor issues like worn piston rings reducing compression ratio directly affect high pressure buildup. Additionally, overcharged refrigerant or air contamination can disrupt pressure balance. Regularly replacing the dryer is crucial as it absorbs moisture to prevent system corrosion. When noticing weakened AC cooling, immediate pressure testing is essential to avoid damaging the entire system.
