What Causes Low Pressure or Negative Pressure in Car Air Conditioning?
3 Answers
This phenomenon is most commonly caused by the closure of the expansion valve or blockages in components such as the dryer filter. It is recommended to first check whether the expansion valve is in the open position and ensure it is functioning properly. Next, turn off the air conditioning, wait for the high and low pressures to balance, and then restart the air conditioning to locate the approximate position of the refrigerant blockage. In these locations, components like the dryer filter and valves are likely to be clogged with dirt. Introduction to Car Air Conditioning: The car air conditioning system (air-conditioning-device), commonly referred to as car AC, is used to regulate and control the temperature, humidity, air cleanliness, and airflow within the car cabin to optimal levels. It provides a comfortable environment for passengers, reducing travel fatigue, and creates favorable working conditions for the driver, playing a crucial role in ensuring safe driving as a ventilation device. Air Conditioning Layout: Different types of air conditioning systems have varying layouts. Currently, the most widely used in passenger cars is the integrated heating and cooling air conditioning system. Its layout involves assembling components such as the evaporator, heater core, centrifugal blower, and control mechanisms together, referred to as the air conditioning unit assembly.
There's something weird going on with my car's AC lately—when I turn it on, the air feels neither hot nor cold. After checking with a pressure gauge, I found that the low-pressure side is actually in a vacuum, meaning the pressure is way below normal, indicating insufficient refrigerant in the system. There could be multiple reasons for this, like leaks in the piping causing refrigerant loss, a stuck expansion valve blocking the flow, or an aging compressor failing to draw in refrigerant. The last time I ignored this issue, it ended up burning out the compressor, costing me thousands in repairs, and making summer drives unbearable. For daily driving, it's crucial to regularly check the AC system pressure—get it tested with professional tools at a repair shop every six months or 10,000 km to spot leaks early, top up refrigerant, and avoid suffering in the heat while wasting fuel. Routine maintenance is simple too—keeping the system from drying out can extend its lifespan.
Veteran drivers are quite familiar with the low-pressure negative pressure issue in car AC systems—it's a common occurrence. When the low-side pressure drops too low, it turns into negative pressure, usually due to insufficient refrigerant or a circulation problem. Possible causes include a clogged pipeline from debris buildup in the dryer, a refrigerant leak causing a sharp pressure drop, an improperly adjusted expansion valve failing to regulate flow, or worn compressor brake pads failing to draw in gas. My advice is not to tinker blindly—just use a multimeter to check the compressor and wiring, as voltage fluctuations can also trigger faults. Head to a professional shop ASAP for diagnosis. They typically recharge the refrigerant and perform a leak test with a pressure check. Otherwise, prolonged low-pressure or negative pressure can cause the AC to blow hot air, shortening system lifespan and compromising driving safety. Remember, AC maintenance is a fundamental part of car upkeep—don’t overlook it.
