Strange AC - Aux Fan issue

Greetings,

So this one has me stumped. I've googled, and haven't come up with anything.

Info:
91XJ Laredo I6 4.0 engine

So here's the deal. While the A/C is on and I'm at idle, it blows nice cool air. When i'm driving at low speeds, it's fine as well. The issue is, when I get my engine to a certain RPM lvl, (above 1500, usually around 1700/2000), the AC stops blowing. I took a look under the hood (while in park of course) and revved up the engine. When the RPM's get to around the 2k mark, the AC Clutch disengages (Pulley still spins freely) and the Electric Aux fan also cuts off. When i drop the RPM back down, the Clutch kicks back on and so does the Aux Fan.

This is causing the engine to get hot while driving at freeway speeds.

Please help!!! Summer is getting near and I really can't have this in AZ.

Thanks in advance,

Steven

anyone?

I was waiting for someone to come up with a good answer for you. All I have are guesses and possible things to test. Engine getting hotter at freeway speeds doesn't make sense to me. On the freeway, you should be fine without any fan. One idea I would throw out to try is to jump across the pressure sensor plug on the accumulator bottle to see if it still cuts out at 2000 rpms. If it stays on then, try replacing that sensor (assuming your charge is good because you get cold air). You can replace that sensor without loosing refrigerant.

Why would it cause my aux fan to cut off though? I mean, the AC shouldn't disengage at 2k RPM in the first place, but why would that cause my Aux fan to cut off as well?

Check your vacume resovour (sp?) for a disconnected vacume hose or a hole in the resovour itself. You didn't mention the year but I had the same issue with my 93' when I got the RPM's up the AC would cut out. Look behind the passenger side of the front bumper for the resovour (unless you have moved it like some of us have done). I filled the hole in my resovour with a dab of RTV silicone.

The aux fan fan is designed to turn on when the a/c turns on. So if you have a fault in the a/c compressor and it shuts off, the fan shuts off which is normal. Sounds like you need to find the cause of your a/c shutting down. Also, the aux fan will kick on by itself if you reach a certain temp. I think it is around 230 degrees.

jelrod said:

Check your vacume resovour (sp?) for a disconnected vacume hose or a hole in the resovour itself. You didn't mention the year but I had the same issue with my 93' when I got the RPM's up the AC would cut out. Look behind the passenger side of the front bumper for the resovour (unless you have moved it like some of us have done). I filled the hole in my resovour with a dab of RTV silicone.

Click to expand...

I did mention the year, right under "Info:". It's a 91.

The leak in the vacuum res wouldn't surprise me. Being that i've been through some mud recently and it very easily could have dried out. I'll give that a check.

Thank You and I hope that's it!

Steven

If your AC were overcharged or you have moisture in the lines, you may be increasing the high side pressure above the limiting switch and the switch might be doing it's job and protecting the system from self destruction also. I'd put a gauge on the system and see if the pressures are sky-rocketing before it cuts out. If so, evacuate and try refilling with the correct amount.

I don't think the 91's have a high pressure cutoff (I could be wrong), but I would have someone check the pressures. I think Shorty's on the right track.

LiquidOps said:

I did mention the year, right under "Info:". It's a 91.
Steven

Click to expand...

Sorry, reading too fast. :looney:

You ac system is slightly under charged.

Also there isnt a high pressure cut of switch

hole in the vacuum canister would be my guess make sure you check that

bigkeegs said:

hole in the vacuum canister would be my guess make sure you check that

Click to expand...

That just moves the vent door, does not affect compressor or aux fan.