I’ve got a 1998 Durango SLT 5.9 4wd with an intermittent AC problem that I hope I can get some help diagnosing.
I took it on a 6 hour trip (3 hours each way) and had a thermometer in the vent so I know the temperature readings are fairly accurate. When it’s cooling it cools great. The air output temperature is about 58 degrees. But when it stops cooling the temperature goes to 80 degrees and holds at 80 degrees – not 85 or 75 degrees, 80 degrees.
I have not been able to determine what triggers the temperature to rise or fall. Sometime everything is great for an hour and other times only about 15 minutes. Same thing when it reaches 80 degrees. One time it stayed at 80 for almost an hour them all of a sudden the temperature dropped to 60 (less than 2 minutes). The system appears to be charged properly and the compressor appears to be running fine – I believe that the system running properly about an hour before rising to 80 also shows that the cooling components are working properly. Could this be a faulty thermostat in the heat/cool system? Why does the temperature only go to 80 and hold at 80? Has anyone experienced symptoms like this?

 

it almost sounds to me like your evap coil (under the dash) is freezing up, then the compressor shuts off until it defrosts, are you running it on the 'max a/c' setting? if so you sh4ould have the fan on high to prevent this.

pete will have more info for you, but this is what my gut tells me is going on

 

I considered that the evap is freezing up but when it "decides" to cool the temperature goes from 80 to about 60 in under a minute. And when the temperature rises, it takes about 2 minutes. I would think that if the coil was frozen that the temperature would creep up and down. But I may be wrong.

1 other thing. My wife reminded me that we slowly loose coolant. Once when driving with the AC on she had a "coolant mist/steam" coming out the defrost vent - right in-front of the windshield. She said it lasted about 15 to 30 minutes and slowly dissipated and she hasn't seen it since. I checked to make sure the air flow for the heat/defrost/ac is gong to the correct location and when I adjust the ***** on the dash it appears that the airflow is discharging at the proper location. But I don't understand why she had airflow (coolant mist/steam) coming out the defrost vents when the AC was on. I don't feel any airflow out the defrost vents when I checked it in the driveway last night.

 

I would get a set of gauges to further look at this issue. See what the pressure readings say when this occurs. if the pressure readings cannot be maintain within a normal pressure range (low side) this may indicate a possible bad expansion valve.

As far as the mist? that's odd to see mist coming out of the vents if you are running in cooling mode. Even if the heater core is leaking, you should not see mist coming out the vents in cool mode. This may indicate the blend door is not sealing tightly between heat/cool modes. The blend door may be bleeding in hot air plus leaking coolant into your cooling mode if you see mist coming out of the vents in cooling mode.

Check all your vacuum hoses to make sure none are bad.