My A/C stops working once I get on the freeway. The fan still blows but the air is warm. Any clues on what the problem might be?

Thanks

 

ac is oevr rated; thats why the windows go up n down, my AC has never worked on my XJ.

 

haha true, but I only use the AC on the freeway when having the windows down screws with MPGs.

In which case. anyone have any clues of what is wrong or how I can fix it without taking it to a shop?

 

Could be to much head pressure, or not enough pressure.
My XJ doesn't have A/C ever.
So I don't know if its got an expansion valve or orifice tube.
Either one could be plugged reducing flow making head pressure to high and the switch cuts it off.
It could be low on gas, making it shut off, or cycle excessively and not cool.
Either way without a set of gauges its hard to diagnose.
Get a cheap set from Harbor Freight and report back with the high and low side readings and I can help more.

 

is it dripping water and big puddle under it hours after it is turned off and parked? if so we are in the same boat.
I think mine may be the low pressure switch.
the evaporator freezes up and that is why all the water later on..it's melting.
I have these links so far but it is too cold in NY to do any testing unless I have the truck indoors at 70*.
A/C loses power after 40 minutes - Page 2 - JeepForum.com
AC compressor cycling - Jeep Cherokee Forum
A/C Only Blows Hot Air, Plenty of Freon.... - JeepForum.com

 

Sounds like your is freezing up, more an issue of it being to low on gas.
To little gas drops the low side pressure and reduces the evaporator to below freezing and it accumulates ice on it.

Gauges are marked with PSI, but they're also marked with temps too. That is what your reading on the low side and you actually look at the pressures on the high side.

 

TY!

 

Is the compressor shutting off or just blowing warm air?

On the freeway manifold vacuum is lower. If you have a small vacuum leak under the dash, the blend door may be closing to default - warm. It's still making cold, but you aren't getting it.

Engine off, Ignition on, AC controls to ON, COLD.
Find under the hood where vacuum goes through the firewall - disconnect, have someone blow cigarette smoke through the line to the dash. Look for any place where smoke comes out under the dash. Where it comes out is where the vacuum loss is - repair as needed.

 

Cool trick!

 

Look at the coil in your compressor clutch - it gets weak over time and with heat, and cannot engage the clutch. Thats why it will work when coll, but stops after you warm up or run hot.

 

Ive never had a/c in any of my jeeps ;P

 

If the compressor clutch is slipping you'll see black powder residue all over the compressor from the clutch surfaces burning. Probably you'll smell it too.
Rev it up with the ac ON that duplicates the freeway driving for the compressor - if slipping you'll see sparks!

 

The coil is electomagnetic, its either good or its bad, as long as your getting 12v to it.

You can find the clearance spec someplace and check that the clutch gap is within spec. I've had semi trucks that use the same style compressor, and it typically if the gap looks okay its okay. Anywhere from 1/16" to 1/8" is about right, at 1/4" gap it starts to get a little flakey on if the clutch will engage every time.
Its also nearly impossible to replace the clutch on one of thee without knocking the front bearing out and having to replace it and the seals.

 

True - if the gap is too large it has trouble pulling in. But once it's engaged the gap is gone, it won't "let go" just because of speed.
If it's worn out, the surfaces get scored, then it can slip - thereby making the black dust and sparks.

A new clutch runs $$$ almost as much as a new compressor, and as said, often the compressor seals get destroyed replacing it. Plus you need the right tools.

But - it sounds more like a small vacuum problem letting the blend door open when manifold vacuum is lower at freeway speeds.
Easy to check: After a freeway run with AC on, feel the hoses around the drier up front - are they cold? If yes, the compressor is working along with the AC system. It's just not directing the cold air into the cab.
The cigarette smoke test will very quickly find the leak. It's a fairly common problem.

Otherwise you could spend hours looking for it and still never find it.

For those like me that are afraid using the smoke might get them started smoking again - I'm still battling the urge after 17 years.
Simply hook a vacuum hose to a tee, one end to a vacuum port, the other end you blow in, and the tee portion put a burning cigarette in a hose. When you blow air in, the venturi effect at the tee pulls smoke in and into the manifold. Works as good or better than a $2000 smoke machine.

Please be sure to let us know what you find.

 

If it happens fairly quick and all the time on the highway, I would say vacuum leak. If it gradually happens, try turning it off for 5 min and then on, if it comes back then its freezing.