Two common sources of that include a bad blend door inside the HVAC enclosure or a vacuum leak. The HVAC system is vacuum controlled and the air temperature sent into the passenger compartment is controlled by an electrically actuated blend door that mixes hot and cold air.

 

That was one of my first thoughts, but when I swap modes between warm and cold air, I can hear the blend door usually moving and/or closing. I'll run through that gamut here as soon as the rain stops; be pretty nice and easy if thats it.

 

Have you confirmed if the compressor is running, is the clutch engaging.

could be low/no Freon, if so, could be a leak from a number of point, bad clutch, pressure switch, etc.

 

Whats the visual on the clutch engaging? Seems to be running, but I'm not seeing anything that distinctly looks like engagement.

 

Are you getting any iced over lines? verify your hi- and low-pressure relays/switches are plugged in. I'm in the middle of doing mine. waiting on my vacuum pump and gauges to get here. Kit with compressor, dryer and expansion value was $268. Came with oil and O-rings, too. can send you a link if you want.

 

When you have the system on and you look at the center of the clutch, is it rotating or still. If rotating, can you grab the return line and feel cold? Or is it the same as everything else?

 

Posting a pic; taken while the engine was running and for all signs and indications, the AC turned on in the cabin. I -think- this is the AC clutch, shown by the white arrow, and if it is, it is definitely stationary and not turning.

 

OK, no turning means no function. My next step as an AC professional would be to check system pressures with some manifold gauges. You will probably find that the refrigerant has leaked out of the system and the low pressure safety switch is not letting the clutch to engage

 

Noted. Might have to drive that one to a professional with the actual gauges to use.

Quick back story; I bought the Jeep in 2008. Been with me all over the World since I'm active duty military. Had it in Spain most recently, and noticed the AC was weak. The only freon I could get on base at the time was the one that had the dye for leaks in it. But, it worked and I had my AC back. Flash forward, I have it back here in the states, and a few months ago, noticed it was weak. I once again bought the same freon that had the dye in it because it was just simply cheaper and it had worked before. Regretting it now, but lesson learned. Is it possible that the cheaper stuff lost pressure more quickly, and I should go ahead and spring for a more expensive brand, or would you suggest more encompassing steps before I invest that direction?

 

I get R134 for about $10/can when I need it from Walmart or tractor supply, don’t know if being cheap means lesser quality.

freon, generic name, does not wear out or get used up. The only reason a charged system would be low is a leak somewhere, compressor seal, hoses, evaporator, condenser, etc. and leaks don’t fix themselves, they either stay the same or get bigger.

I know i may get slammed for this but, just this year, after 23 years of use, I had to add a can to my 2002. Adding some Freon is my first go to. If it leaks out in a few months, I start looking for leak. If adding a $10 can gets me through a season, I consider it a small price to pay.

i had similar on an older Tahoe we have, adding a can would gets us through a season until this year, then I found the high pressure valve leaking and replaced it.

 

From one vet to another, thank you for service. Most of the time the leaks are at the connections because the O rings get hard. So if you end up doing any work on it, replace them all.

 

Fun little update: So I took chance and bought some freon, and loaded it into the system at the low pressure port. Didn't really do a whole lot, but I kept pushing it in, thinking it would hit a cap, and then the compressor kicked on. Intermittently. Drove it with my son for a bit to his after school event. Wasn't blowing cold air, so when I got there, I opened the hood, added some more freon, and saw the clutch wasn't engaging. I poked it with a metal rod and it kicked in. Problem solved!

Or so I thought.

Worked for about 20 minutes, then the air started coming out warm again. I turned the vehicle off and gave it a break. When we left to go home, compressor was working at the get go and about 20 minutes in, shut off again. So my gut says the stock compressor is finally starting to kick the bucket, or maybe the cheap freon with the dye in it added up and is gunking it up. I was advised to try a system flush, which is still cheaper than the alternative of buying a new one. So gonna be pricing that out here in the next day.

 

“So my gut says the stock compressor is finally starting to kick the bucket, or maybe the cheap freon with the dye in it added up and is gunking it up.”

No, you have a good size leak. Adding the Freon, got the pressure up enough to satisfy the low pressure switch, got the compressor running, but then the Freon leaked out again.

we keep telling you the only reason you have to add Freon is that you have a leak. You just proved it.

sure, you may also have other issues, but the leak is causing the low pressure switch to keep the compressor clutch for coming on.

 

The freon pressure must be within limits... it can't be too low or too high... or the low and high pressure switches will prevent the compressor from being enabled by its clutch.

 

OP, don’t forget to post an update, especially if you find the problem(s) and get your ac system cooling again.

 

Update time. Work had me by the throat, but finally had a bit of time to tinker with things.

AC kicked on a few times when I poked the clutch with a metal pole. Intermittently. I did hook up a pressure sensor to the low pressure port and it showed within tolerance, even after a week of driving; its at the exact same spot (right in the middle of 'full') today as it was a week ago. So it doesn't -seem- like its leaking. Which leads me back to thinking its the low pressure sensor itself, (it is the 2000 stock sensor, so its not unfathomable that its failing after 25 years of faithful service). Incidentally, the fact that it did kick in when I poked the compressor clutch, after sitting for a week, makes me wonder if the clutch itself is sticking or finally showing its age.

For thoroughness, I did try to inject more freon in, and it was not taking anymore into the system. I looked around with a UV light for any dye leaks, and didn't see anything anywhere on any line, connection, nothing glaringly or subtly obvious.

So I'm at the point of finding new sensors and replacing them, and barring that, bringing it to a specialist that can pin point a hidden leak that I can't find, or confirm that my compressor is about to go the way of the dodo. I was -very- thorough in looking over every connection, line, gasket, everything I could to find any of the dye, and did it at night so there was no chance of seeing something bleeding out in the sunlight, but I'll be the first to admit that I'm not a pro at AC stuff.

Couple of the guys at the local jeep chapter went the way of the logical pattern here too, thought it was a leak, checked for the leak, found no leak, then realized it could pretty easily be the low pressure sensor. I'm waiting for the Jeep to cool down after driving, then gonna take the low pressure sensor off and give it quick inspect and clean.

 

The clutch does also wear out, in case no one has mentioned it yet

 

Have you tried a paper clip. Unplug the connector at the lo pressure sensor, use a paper to jumper across the contacts of the connector.

 

Now THAT is the quality content I came here for. Checking that out right now, updates here in a few.

 

if you jump power straight to wire to compresses clutch does it run
if not problem is withing clutch itself
and poking clutch with a metal pole is not a good diagnostic step as it does not tell you if clutch is staying open from an electrical vs a mechanical issue

 

Jumped the clip and had working AC, absolutely. Ordered a new sensor already.

And yeah, the clutch poking was more me just idly wondering what would happen if I poked and moved it; maybe the bearing went bad, and poking it a bit aligned things enough to kick on for a second before it became imbalanced again and locked up, thus ferreting out a potential mechanical issue smoking gun. Not a normal step, but sometimes some light percussive maintenance can give a little direction.

 

I’ve never on my TJ before, but on other vehicles, when you remove the sensor, you “open” the system.

maybe TJs are different,

my belief, while could be bad switch, Freon is low.

 

Leave the paper clip in and drive vehicle around with thermometer in dash vent, should get down close to 40.

 

I suggested doing that on the first page of the posts. That sensor is there to protect the compressor against not having oil suspended in the refrigerant going through it. If you remove that sensor, you will lose all the refrigerant. But if you jumper across it your system will work.