Why Are Both Low and High Pressures in Car Air Conditioning High?

[EmilyAnn]

Reasons for both low and high pressures being high in car air conditioning: 1. Under normal operation of the air conditioning, the low pressure is around 3 bar, and the high pressure is around 15 bar. Note that this is when the air conditioning is functioning normally, meaning the cabin blower is set to the fourth speed, the radiator cooling fan is running at high speed, and the external condenser is dissipating heat effectively. 2. If your air conditioning system shows high low pressure and low high pressure during normal operation, it could be due to insufficient compressor displacement or a malfunctioning expansion valve. Here is some related information about car air conditioning: Brief Introduction to Refrigeration Principle: 1. After the user starts the car air conditioning system, the compressor operates, driving the refrigerant to circulate within the sealed air conditioning system. The compressor compresses the gaseous refrigerant into high-temperature, high-pressure refrigerant gas, which is then discharged from the compressor. It flows through the pipeline into the condenser, where it dissipates heat and cools down, condensing into high-temperature, high-pressure liquid refrigerant before flowing out. 2. The high-temperature, high-pressure liquid refrigerant enters the dryer reservoir through the pipeline. After being dried and filtered, it flows into the expansion valve for throttling, undergoing a drastic change in state and turning into low-temperature, low-pressure liquid refrigerant. This then enters the evaporator, where it absorbs heat from the air passing through the evaporator, lowering the air temperature and blowing out cold air, thereby producing a cooling effect. 3. The refrigerant itself evaporates into low-temperature, low-pressure gaseous refrigerant after absorbing heat. It is then sucked into the compressor through the pipeline, compressed, and enters the next cycle. As long as the compressor continues to operate, the refrigerant will circulate continuously within the air conditioning system, producing a cooling effect. When the compressor stops working, the refrigerant in the air conditioning system stops flowing, and no cooling effect is produced.

[AliceRose]

I just encountered this issue where the AC wasn't cooling and was consuming more fuel. After checking, it turned out that too much refrigerant was added, causing the pressure to skyrocket. Poor cooling system performance often leads to abnormal high and low pressure as well, such as when the fan isn't working or the condenser is clogged—just like my car last time after a long trip, it was covered in bugs. Additionally, air entering the AC system can cause unstable pressure, in which case you need to vacuum and recharge the refrigerant again. I recommend not adding refrigerant casually by yourself; it's most reliable to go straight to a repair shop to check the pressure gauge.

[DiDaniela]

I've researched this issue, and there are three main reasons: First, excessive refrigerant increases pressure, making the compressor work harder. Second, poor heat dissipation, such as a faulty radiator fan, dirty condenser, or deformed pipes affecting heat dissipation. Third, a stuck expansion valve prevents the refrigerant from circulating smoothly, causing pressure buildup. Last time my car's AC stopped working because of this, and it took several attempts to diagnose that the condenser was too dirty. If you encounter a similar situation, I recommend cleaning the radiator fins first, and if that doesn't work, check other components.

[AubreeLee]

High pressure on both the high and low sides of the AC system usually indicates a blockage in the system circulation. The most common issue is heat dissipation, especially noticeable during summer traffic jams when high engine compartment temperatures affect condensation efficiency. It could also be due to overcharging of refrigerant—I've seen cases where novices added too many cans of Freon, causing pressure to double. Another possibility is air mixed in the refrigerant or deteriorated lubricating oil obstructing circulation. After turning on the AC, observe whether the engine compartment fan is running—this is the most straightforward way to diagnose a heat dissipation issue.

[WyattAnn]

What annoys me most when repairing cars is encountering this kind of issue, which actually has quite diverse causes. Poor condenser heat dissipation is the most common, with leaves and insect blockages accounting for at least half of the cases. Overcharged refrigerant is also a frequent cause, especially in summer when roadside shops rush the job by over-pressurizing. Other issues include air entering the refrigeration system or expansion valve failure, causing liquid refrigerant to accumulate in the high-pressure side. My advice: rinse the condenser fins during regular car washes and periodically check refrigerant pressure. If the compressor fails, repairs can cost thousands.

[LeNova]

This issue puzzled me for half a year before I understood the principle. Simultaneous high and low pressure exceeding standards is like a traffic jam on the highway, causing poor refrigerant flow. The key lies in the heat dissipation efficiency of the condenser—issues like fan failure or blocked cooling fins can lead to heat buildup. It could also be due to insufficient expansion valve opening or refrigerant purity problems; moisture and impurities in the system are troublesome. From my own experience, it's best to check the engine compartment for debris before driving in summer. If the AC pipes frost over, stop using it immediately—don't wait until the compressor fails to regret it.