Why does my car A/C compressor keep turning on and off?
An air conditioning compressor that repeatedly spins, catches, and stops causes low airflow for both cooling and heating. This short cycling prevents the system from maintaining stable pressures, leaving drivers frustrated by a lack of proper cabin climate control.
What the numbers show
Counted from the threads quoted below. How we count
- The most recent one is from October 2026.
- This comes up 11.4× more often in r/hvacadvice than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Replacing the vacuum hose going into the vacuum chamberDid this help you?
- 2Replacing the PCV valveDid this help you?
- 3Checking refrigerant and freon levelsDid this help you?
- 4Testing sensors or hooking up a manifold gauge setDid this help you?
- 5Adding dye to the system to inspect for leaksDid this help you?
- 6Spraying soapy water on valves and connections to look for leaksDid this help you?
- 7Using an electronic leak detector or UV glasses and lightDid this help you?
- 8Replacing relays multiple timesDid this help you?
- 9Replacing the high-side pressure switchDid this help you?
- 10Using a scan tool to check live sensor dataDid this help you?
- 11Checking wiring against the wiring diagramDid this help you?
- 12Posting pictures of the wiring for reviewDid this help you?
- 13Setting the thermostat to an artificially low temperature to force the compressor to run continuously.Did this help you?
- 14having a supervisor check the air handler and refill refrigerantDid this help you?
- 15Checking or replacing the radiator fan, testing refrigerant charge, or inspecting the expansion valve.Did this help you?
- 16revving the engine while idlingDid this help you?
- 17regassing the air conditioning systemDid this help you?
- 18checking thermostat wiringDid this help you?
- 19calling a technicianDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Changed it to a new one with the same specs and now the fan is running and restarting every few seconds and still not blowing cold air indoor”source ↗
“If my guess is correct I must have wired it incorrectly and and I can rewire it. Although I am pretty sure I wired it exactly how the old capacitor was wired.”source ↗
“I have a 5,000 BTU window AC in a slightly larger room than its rated 150 sq. ft. I set it to 60°F, but the compressor shuts off when the room is around 68°F. I’m also not seeing much (or any) water draining outside.”source ↗
“What’s confusing is that I’ve purchased two other window ACs in the past, and both did the exact same thing they would shut the compressor off before reaching the set temperature.”source ↗
“I’m setting it to 60°F because I want the AC to keep running continuously. That way, I can manually turn it off when I want rather than having it shut off on its own before the room reaches the temperature I’m trying to maintain.”source ↗
“Anyway, I have noticed that the systems runs for about 5 minutes than turns off 5 min or so later is turns on again only runs for a few than turns off again.”source ↗
“Anyway it keeps running in 1st stage and stopping never getting to the 2nd stage.”source ↗
“The compressor is like jumping starts in the video, while the fan outside is constantly working during these jumps.”source ↗
“And this only occurs when the room temperature is close to the set one, for example, I set to 79, and AC works fine until the room cools down on 79 degree then the AC will have this issue.”source ↗
“This gear/module will spin, catch and stop, then start up again. Is this normal, or is there an underlying issue I'm not seeing?”source ↗
“Because I have little air flow in both my a/c and heat, that's why I'm trying to fix it”source ↗
“My new compressor is now short cycling and the pressures I get are 20-25psi low side and 150-175psi on the high side at 85F ambient temp.”source ↗
“Does anyone know what could possibly be causing this? About to shoot the damn truck”source ↗
“Any way to fix a/c compressor don't stop ? Replace 3 time my relay. 3 time the presostat. (Sensor on the high side)”source ↗
“At idle, the A/C does cool, but it struggles and the cabin takes a while to cool down.”source ↗
“my gauges were doing this: the high side would rise to around 250 psi, while the low side would drop below 25 psi, and then the compressor would disengage.”source ↗
“On a hot day it is more noticeable that when idling the A/C gets warmer. I've regassed it, it was low on gas, but issue persists. The compressor cycles approximately every 10 seconds.”source ↗
“Main issue is when standing long time in traffic, otherwise the issue is not very noticeable when driving.”source ↗
Where this came up
People with this problem also raised
- 2Why does my AC compressor run continuously and never shut off?
- 3Lights flickering when the AC turns on
- 4Why does the outdoor AC fan stop while the compressor keeps running?
- 20AC making loud noise again after repair
- 3Is it safe to drive with a noisy AC compressor pulley?
- 3Why won't AC compressor clutch engage manually?