I have a 2001 Dodge Ram and my A/C and air vent blows hot air intermittently.

After about 5 minutes with the A/C on, it will start blowing hot air...Not just warm, but hot like the heater is on full blast. It will blow hot for 30 seconds to a minute or so and switch back to cold. It cycles between hot and cold every 30 seconds to minute or so. The same thing happens when I'm just using the vent...cool outside air for a while, then a blast of heat. I noticed that if I turn the A/C or vent off while it's blowing hot, then turn it back on, it blows cold again immediately.

I took it to an A/C guy, and he topped off the charge and fixed a leak. He also said the compressor seems to be working just fine. It still has this problem.

Anyone have any idea what's causing this?

 

Sounds like a faulty blend door. Either hangs up or getting an intermittant vac signal or lack thereof. Don't go to that a/c shop again. They should have found that right away and without adding any refrigerant. Check your vac. lines under the dash and at the control head. Also check the blend door actuator.
WC

 

Correction: the blend door is electric, the recirculate door is vac operated. But either could give you your problem. Maybe just a loose wire.
WC

 

Thanks for posting this, my '99 Ram does the same thing which is really annoying to me since I drive with the vent open and the fan on pretty much all the time. Mine only does it when it's not set to A/C (just vent). Please post when you fix the problem

--Kevin

 

Thanks for your input, guys. I drove around this weekend to see if I could gather any more clues. Right before the A/C gets hot I detected a slight change in the sound of the airflow. I can also hear a very slight thump, kind of like a small door closing. It seems the blend door diagnosis may be spot on. This is exactly why these boards are so cool. Thanks!!!

 

Ok, so how do you access the blend door, or control head? Where is it located? Thanks!

 

Cant post the link but heatertreater.net has the fix for that. The blend door is above the motor next to the transmission hump on the passenger's side. I had the same problem. The plastic piece that turns the blend door from the actuator cracks. Best 30$ I spent.