What Causes No Pressure in the Low Side of a Car's Air Conditioning System?
2 Answers
The reasons and solutions for no pressure in the low side of a car's air conditioning system are as follows: 1. Reversed live and neutral wires in the AC power supply: Main symptoms: This usually only occurs during the installation of the car's air conditioning. Solution: Reconnect the live and neutral wires correctly. 2. Damaged fan or capacitor in the indoor or outdoor unit: Main symptoms: If the outdoor unit fan is faulty, the main symptoms are excessively high exhaust temperature or high pressure; if the indoor unit fan is faulty, it manifests as frost formation on the indoor unit. Solution: Replace the damaged fan or capacitor in the indoor (or outdoor) unit. 3. Refrigerant leakage or substandard refrigerant quality: Main symptoms: Both the indoor and outdoor units of the car are operating, and the compressor is also working, but the car's air conditioning fails to provide cooling. Solution: Check whether the issue is due to refrigerant leakage or poor quality, and promptly add or replace the refrigerant. 4. Damaged or faulty compressor capacitor: Main symptoms: Both the indoor and outdoor units of the car are operating, but the compressor does not rotate and may cause overheating. Solution: Check if the compressor capacitor has poor contact or is damaged, and replace it promptly if necessary.
I remember the first time I encountered no pressure on the low side of the AC system, the car completely lost cooling. This is usually due to a severe refrigerant leak, possibly from cracks in the AC lines or loose/aged fittings. Another common cause is compressor failure, such as internal component wear or seizing, leading to an imbalanced pressure system. If the expansion valve is clogged or broken, the low-side pressure will also be abnormally low. I recommend first using a professional pressure gauge to test system readings—anything below 10 psi on the low side is a red flag. Never casually top up refrigerant yourself, as it might mask the issue and waste money. It’s best to visit a repair shop promptly so technicians can use an electronic leak detector to locate the source. Ignoring it long-term could lead to complete AC failure, fogged-up windows while driving, and increased safety risks. A yearly pre-summer AC pressure check can prevent these frustrating failures. Bottom line: don’t delay when this happens—safety comes first.
