A few months back I noticed that when I had it on vent (not A/C) the temperature **** (red/blue) no longer worked correctly in my truck. I could only get it to blow Hot or Cold, nothing in between no matter where I set the controller. It didn't bother me too much because it was winter/colder.

The other day I had the A/C on full blast and it all of a sudden started blowing HOT air. I had to turn the A/C to off and then back on. It did this about 3 or 4 times within 10 minutes or so of driving.

Can anyone tell me what they think is going on? What can I do to troubleshoot it?

I know absolutely nothing about the A/C system. A co-worker of mine knows a little bit. He said if I can get a service manual in .pdf form and some ideas of what to check he might can help me with it. Anywhere to download this?

BTW this is on a 99 Ram Quad cabe w/5.9 360.

thanks

 

Sounds like your system has a refrigerant leak and there is no more refrigerant. Take it to an A/C shop and have it inspected.

 

Even though it does blow cold? And when it went to Hot, it was instant, it didn't just gradually get warmer and then hot.

Just to clarify (and I edited my above post) the issue with the temp ****/control was when I just had the vent on (NOT A/C). It didn't matter if I was getting fresh air from out side or recirculating air in the cab. It was only cold or hot, no in between.

 

First have a buddy stand over the engine with your truck running. Start with AC off, the compressor clutch should not be spinning. Then turn on the AC and watch for the clutch to start spinning. If it starts spinning your compresssor is fine and the air should begin to get cold. Then have your friend stay out there and tell him when the air becomes warm See if the clutch is still spinning... If it is you have a leak/clog/bad evap. If it stops spinning your probably tripping one of your safties such as a pressure switch.

 

Or possibly the duct or vaccuum issue to it. It might be shutting/opening and going to heat side.
Got this from Chrysler parts direct.

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a vacuum problem wouldnt change heating and cooling only the location of the air blowing out would

 

Not sure if you are still having issues, but if so, try this. Turn you thermostat to midway between hot and cold. This has something to do with either a checkvalve under the dash, or a flap opening up and letting pure engine-heated air in through the ducts. It will do it on vent also. I can soetimes hear the duct closing shut about the time it happens in mine, but since I have left the thermostat at the mid mark, it has worked for 3 months straight. I know it is not a fix, but in the middle of summer is no time to not have the cold air kicking! If anybody has any other ideas, please, let us all know!!