What Causes the Fluctuation of the Low-Pressure Gauge in a Car's Air Conditioning System?

3 Answers
DeMaya
07/29/25 1:58am
Fluctuation of the low-pressure gauge indicates a significant amount of moisture in the pipeline. Additional information is as follows: 1. Car Pressure: The normal high-pressure range for a car's air conditioning system should be between 1.3 to 1.7 MPa; the low-pressure range should be between 0.1 to 0.25 MPa to be considered normal. 2. Testing the High and Low Pressure of a Car's Air Conditioning System: When the engine throttle is increased, the low pressure should decrease with the engine's RPM. The faster the RPM, the quicker the pressure drops, indicating good compressor performance. If the opposite occurs, it suggests a compressor malfunction. When the compressor is operating, maintain the engine speed between 1500 to 2000 RPM and activate the air conditioning to engage the compressor. Under normal conditions, the low-side pressure should be approximately 150 to 250 kPa, and the high-side pressure should be around 1400 to 1600 kPa.
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StGeorge
08/12/25 11:55am
I've experienced shaking in the AC low-pressure gauge while driving, which is usually caused by unstable pressure inside the air conditioning system. The most common reason is uneven pumping by the compressor, where internal blades or pistons are worn, causing intermittent refrigerant flow. The expansion valve could also be problematic—for example, if its function of regulating refrigerant flow fails, leading to fluctuating flow rates. Another common issue is air or moisture contamination in the system, just like in my car last time when a small leak allowed impurities to enter, causing pressure fluctuations. Insufficient or excessive refrigerant can also affect the overall circulation efficiency. If not addressed promptly, the shaking can reduce AC cooling efficiency, increase fuel consumption, and in severe cases, damage core compressor components. I recommend visiting a professional repair shop immediately—they can diagnose the issue using pressure gauge tests, and usually, replacing a component will solve the problem. Remember, regular maintenance can prevent such issues, ensuring a comfortable and safe cabin environment.
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JanelleRose
10/02/25 3:22am
From a repair experience perspective, low-pressure gauge fluctuations often indicate system instability. Possible causes include aging internal compressor components, such as worn piston rings or damaged bearings, leading to inconsistent refrigerant output. Faults in the expansion valve, like blockages or regulation failures, can also trigger similar issues. Impure refrigerant or residual air in the system will cause pressure fluctuations. During diagnosis, pressure gauges are commonly used for monitoring - severe fluctuations typically indicate mechanical defects. Additionally, poor electrical connections or blown fuses may amplify the fluctuations. I've encountered cases where delayed repairs resulted in significantly degraded AC performance and wasted fuel. Early intervention can save major overhaul costs. A comprehensive system check by a technician - including pressure testing, condenser cleaning, and recharge with pure refrigerant - usually resolves the issue.
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