What are the symptoms of a faulty air conditioning pressure switch?
4 Answers
Car air conditioning pressure switch failure manifests as: poor contact of the contacts or abnormal operation of the pressure switch, resulting in the compressor not working or failing to provide normal pressure protection. Car air conditioning pressure switches are divided into low-pressure switches, high-pressure switches, dual-temperature switches, and three-stage pressure switches. The inspection methods for car air conditioning pressure switches are as follows: 1. Check the continuity of the pressure switch: Use an ohmmeter to measure the resistance between terminals 4M1 and 4M2 of the pressure switch. The resistance should be 0. If the resistance is not 0, it indicates poor contact of the normally closed contacts of the pressure switch, and the pressure switch needs to be replaced; if the resistance is 0, proceed to performance testing of the pressure switch. 2. Check the performance of the pressure switch: Verify the operation of the pressure switch under specified pressure conditions. If the test results are abnormal, replace the pressure switch.
When the air conditioning pressure switch fails, the most common symptoms are the AC system not working at all or having extremely poor cooling performance. I often encounter this issue when repairing cars, where the owner reports that pressing the AUTO button yields no response from the AC. The fan might still be running, but the compressor just won't start because the pressure switch cuts off the circuit when it fails to detect normal pressure. Sometimes, this is accompanied by an abnormal pressure warning light, especially during hot weather or after long-distance driving. If you pop the hood and listen, the absence of the compressor's humming sound is a classic sign. I recommend avoiding DIY attempts and instead using a professional pressure gauge to check whether the high and low pressure values are within the normal range. Abnormal readings indicate a faulty switch. Ignoring this issue can lead to compressor damage, resulting in even higher repair costs. It's best to visit a dealership or a trusted repair shop promptly to have a technician replace the switch—after all, enduring summer heat without AC is unbearable.
The symptoms of a faulty car air conditioning pressure switch are quite obvious, and I've experienced it myself before. That time on the highway, the AC suddenly stopped cooling, making the car unbearably hot. The fan was running loudly but no cold air came out at all. The compressor didn't engage at all - this is a classic sign of a failed pressure switch. Another symptom is when the AC system cycles on and off repeatedly, with cooling performance fluctuating, causing unstable temperatures inside the car. If the pressure is too high or too low, the system will automatically shut down to protect the compressor from burning out. I checked the fuses and they were fine, and it wasn't until I took it to the repair shop that they confirmed it was a switch failure. Drivers should pay attention to these warning signs, especially in older vehicles which are more prone to such issues. When abnormalities are detected, get it checked as soon as possible - safety comes first. Otherwise, long trips can become miserable.
Symptoms of a faulty AC pressure switch include the air conditioning not cooling and the compressor failing to start. I occasionally repair cars myself and know that the pressure switch monitors refrigerant pressure; if it fails, the system stops working to protect the compressor. After turning on the AC, listen for sounds—if the compressor doesn't engage or cycles on and off frequently, the switch may be malfunctioning. During inspection, unplug the connector and use a multimeter to measure resistance changes; abnormal readings indicate damage. Additionally, excessively high pressure on the high-pressure side can cause the system to shut down directly, in which case the pressure gauge readings will be abnormal. Don't ignore these issues—seek professional repair immediately.
