Air conditioner problem

My air conditioner works well when it is working, but on hot days, it will often stop cooling after running for 10 or 15 minutes. If I turn it off for a few minutes, it will start cooling again. My car is a 1995 Mercury Grand Marquis

Your R-134 refrigerant may be a little low and causing the evaporator to freeze up.

Thanks. After receiving your message, I checked the refrigerant pressure on the low-pressure side (I have only a low-pressure gauge), and the pressure was about 40 psi, which is in the high normal range. I am reluctant to add more refrigerant because I might over-charge the system.

I suspect that you are right, however, in identifying evaporator freeze-up as the probable cause of the problem. The question now is just what is causing the the evaporator to freeze up.

If your vehicle uses a “clutch cycling switch” to regulate evaporator freeze-up, it may be failing. Many of these are screwed into a Schrader fitting (like a tire valve) and can be replaced without discharging the system. I’d check that first. A failing switch will not necessarily cause the evaporator to freeze up, but it can stick open, causing the air to not turn back on when it should. This is what was happening to my car a few years ago. (Chrysler model)

(I have only a low-pressure gauge

I am reluctant to add more refrigerant because I might over-charge the system.

Wise decision on your part. I like to leave A/C work to my local shop. (not a chain, and they have been around for over 50 years at the same location (I can remember that far.) The change to new refrigerants makes it just that much more difficult, but with the experience and equipment they have, they are far more effective and efficient than I could be.