Other Mopar A/C problem diagnosis help needed

[WH23G3G]

I've got this 99 Jeep Cherokee 4.0 with 230,000 miles on it. The A/C works good and will leave chilly sometimes. Randomly while driving with the A/C on the cold air will turn into warm damp smelling air for up to a couple minutes and then it will get cold again. I've asked mechanics and gotten diagnosis just by hearing the problem from a clutch gap problem to a cycling switch could be bad. I actually took it to a good mechanic shop and he hooked up gauges and ran in for awhile but it never changed from cold to warm. He said the system is performing fine. But I'm about to take it on a long trip through the mountains and want the A/C to be working right. Cycling switch makes sense, but I've never paid attention as to if it quits cycling when it turns from warm to cold. The one mechanic that hooked up a gauge set to it said it's got a full charge of Freon. The temp gets to like 34 out of the vents. Any ideas? Should I take to another mechanic or swap out the switch?

[A383Wing]

hooking up a gauge set will not tell you how much Freon is in a system. If a system holds 3lbs for example, and the system only has half of that in it, gauges will read the same. Reading the gauges while system is working will tell you a little, but not how much freon it has.

when is the last time you had the AC serviced? (as in full discharge and re-charge)

the switch is like $20 and it can be changes without discharging the system. It screws onto a schrader valve like a tire

Bryan

[WH23G3G]

Most of the time the system is working as it should, it is random when it turns warm. It doesn't do it a particular outside temp. The mechanic said the pressures are in the correct limits for when he was checking it. It has never been serviced since like 2001 or 2002 when I was able to do a evacuate and recharge when I was working at a shop. I don't see an grease or oil buildup on the lines or connections. There isn't any unusual noises. I'm definitely sure an evacuate, accumulator and orifice tube replacement wouldn't hurt but I need to just get me to Nashville and back without losing a/c totally. Is there a way to tell if the cycling switch is failing?

[A383Wing]

is it a 2 wire or 3 wire switch? And where is it located? Pic?

Bryan

[Pete in NH]

Hi,

As Bryan noted system pressures don't really have anything to do with the level of system charge unless it's almost empty. So, its really useful to know if the compressor clutch is disengaged when the system goes over to warm air. I was wondering if could be a blend door issue. Clamping off the heater hose lines might tell you something. Also wondering if the clutch gap might be an issue or an intermittent clutch coil or wiring.

[John_Kunkel]

The warm "damp smelling" air tells me the evaporator is freezing which shuts off the compressor, when the ice melts the system returns to normal and the water running off the coils gives the smell.

[A383Wing]

I thought about air door issue in heater box as well...there are TSB's on that common problem. Everything in there is plastic, and the doors & lever pivots break. Going down the road the door can go anywhere it wants if it's broken.

I have had compressor coils heat up and fail when warm, along with pressure switches doing the same thing.

Bryan

[A383Wing]

I also remember one time the compressor relay quit working after getting warm

Bryan