The AC compressor in my car is turning on and off repeatedly, and not really getting a chance to get cool.

From what I've read this can indicate low coolant. I've just had the system repaired a month ago, so it has a new a bunch of new parts... Original post about AC problems here: 1995 Mercury Mystique - No more cool air from AC

Does anyone have suggestions on how to check if the coolant is actually low, and how to find and repair leaks in the system if there are any? Thanks!

  • Yeah, only a second or two. It clicks on for 1 or 2, then off for 1 or 2, then back on again.
    – jocull
    Commented Sep 13, 2012 at 18:19

2 Answers 2


If you had the system repaired a ago I would bring it back. There is a chance that a component that was replaced is defective. There is also the possibility that you had a major leak that they found easily and now a small leak that may be more difficult to find. I would give the shop the benifit of trying to fix it for free before attempting anything by yourself.

  • Thanks for the suggestion. I'm already a thousand dollars into the whole ordeal and we're exiting the hottest of the weather now. I think I'm going to take it in for at least a check-up and get an estimate and then make a decision.
    – jocull
    Commented Sep 15, 2012 at 19:25

You can check the pressure with a gauge set. The low pressure port is near the battery. If you've got normal pressure, you might have a bad low pressure switch. I'd think it would be on one of the hard lines, but I'd have to look up the location.

To find out where the leak is, you fill the system back up and try and find it. Use R134a with dye added and grab a UV light and glasses/goggles.

Once you've found the leak, you can fix it. The strategy will depend on where it is. If it's a hard line, you can replace the line or just splice it. If it's something like the condenser, you'll need to have it patched or just replace it. You'll need to evacuate the system to work on it. Ideally you would use a vacuum pump and a recovery tank instead of venting R134a to the atmosphere, which is frowned upon.

Once it's fixed, charge the system again. Don't forget some PAG oil for the compressor.

As mikes is suggesting, you might let the shop have another look at it. From personal experience with this platform, after the compressor and accumulator have been replaced, the next suspect is the return line from the accumulator to the compressor. It's not available from Ford, but Vintage Parts should have one (Any good dealer parts department will look up the part and get it from Vintage). I think there is only one line that's not available from Vintage. I can't remember which one, but I remember that it's one that it should be possible to replace with an aftermarket / fabricated solution.

Keep in mind that the defroster setting engages the compressor. Continually spinning it up enough for the low pressure switch to get a reading and shut it down is probably not good for it. If you're not going to fix it for the winter, you should consider pulling the relays in the box under the hood to keep the compressor off. Having the system low/open for a long period of time is not good for it.

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