AC Getting Cranky

The AC in my '99 Jeep GC Ltd. fails for no apparent reason, then starts up again all by itself. It started ~6 mohths ago, and it happened recently. It happens only rarely: when it’s cool out; or when it’s hot out; when I start the car; or when I’ve been driving for 30 minutes; when I turn it on, or when it’s been on. So far it always comes back on again but summer’s coming!

When it fails, does the airflow become warm, or does the airflow stop?

Good question - the fan just quits but air is cool once it comes on again, so cooling does not seem to be the problem.

You need to check for voltage at the blower motor when it is not blowing. If you have voltage and no air, then you have a bad blower motor. If you don’t have voltage, then you might have a bad blower speed switch or relay. I am making the assumption that it fails at all speeds, including maximum. Is this true? Have you ever tried jiggling the climate switches or the key when it stops blowing?

OK, it sounds like someone with more skills than I needs to look at it then and get the answers to those questions. It does fail at all speeds, but I don’t have a long list of incidents to cover all possibilities, it really is rare. I did find that in one event it failed to come on when I started the car, so I turned the ignition off and on again and it still didn’t work. It was in the 90s, so I opened all the windows and in about five minutes it came on again and didn’t fail for a long time.

Before taking it to someone it would at least be worth a look up under the dash at the fan plug. Its probably lodged up under the glove box on the passenger’s side. You might just need to unplug it, clean it, and plug it back in - in other words it might just be dirty/loose.

Good, that sounds smart. If it’s something that’s dirty/loose I’d hate to take it in for service when it’s working and no way to test if they’ve solved the problem for me or not. Thanks for the advice.

These grand cherokees are known for burning up the blower motor resistor and connector. more often on the ones with zone control.

Ah, that’s good to know, I had no idea. Well that’s a match, so it narrows the possibilities. With its just turning 90K miles I’m expecting something to go, but not looking forward to it. Such a great vehicle, like an old friend by now.

Wouldn’t the highest speed still work in that case?

When it quit each time, it just stopped blowing (or failed to start at all). I would only have had it on high briefly when getting in the vehicle in the summer so that was not much of the time. So, in only one situation I can remember, it was on high when I started the engine, but it failed to come on (fan).