General Question

jca's avatar

Why would the air conditioner in my car work intermittently and not all the time?

Asked by jca (35976points) July 9th, 2014

I have a 2008 Honda Civic with about 190k miles on it (yes, it’s time to consider getting a new car). The air conditioner works intermittently. When it works, it’s great – nice and cold like it should be. But then it will stop working. The fan will stay on, the AC light on the dashboard will still be on, but the condenser will stop working.

I can’t predict when it will work. Sometimes it will take a few minutes to go on, sometimes a half hour. Sometimes it shut off after a few minutes and then goes back on, sometimes it will not shut off at all and then it will be fine the whole ride.

The outside temperature seems to have no bearing on the air conditioner’s functioning.

I have had a few times when I was driving at night or in the rain and it stopped working and then the windows got very foggy, which becomes a safety issue.

Do you know why this might be happening? I am willing to take it to be repaired, and I know that these things can cost some bucks, but I am just looking to not get ripped off, which is why it would be nice to try to get an idea of what the problem is.

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5 Answers

jerv's avatar

Low charge is my first guess. Once the engine compartment heats up, the refrigerant expands just enough to allow it to kick in, but until then the pressure is too low, causing the pressure switch to deactivate the system. The charge is right on the edge of “working”,but if it gets much lower, it’ll be permanently down until recharged.

You can charge it yourself for ~$20; they sell R134 recharge kits at Autozone, and it’s almost as simple as recharging a smartphone.

kritiper's avatar

It could be overcharged and causing the evaporator to ice up. When the ice thaws, it works fine. On humid days, not so much. The probe from the thermostatic expansion valve may be loose in the evaporator coils causing the intermittent operation.

2davidc8's avatar

I would agree with @jerv. I had a car with an air conditioner that showed symptoms similar to yours, and a mechanic diagnosed it as low charge. I did not have it recharged because (as I recall) he wanted more money than I wanted to pay for an old car that I wasn’t planning to keep much longer. Had I known that I could do this myself for $20, I might have tried it.

Tropical_Willie's avatar

Sometimes there is an issue with the pulley/clutch on the compressor. I had a Subaru that had a spacer added to adjust the clutch. But first thought is undercharged.

majorrich's avatar

As @jerv says, you are describing a system that is marginally undercharged. I would check your vacuum side pressure and be prepared to add a few ounces of refrigerant. Many dryer assemblies still have the good ol’ sight glasses, but they have covers on them. That’s another way to see if you don’t have a gauge.

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