Hello everyone. I have a question and I hope that someone here maybe able to help me out with it. I have searched and searched and even called a few places and no one seems to know!

I just bought my father's 1999 Dodge Ram 5.9L truck that he bought new from the dealer. It has around 86,000 miles on it and never had any issues like the one I am about to describe. When I turn the vent or a/c on any setting but max I get cool air, at first. Then a few minutes later the air gets very hot, for about 2 to 4 seconds. Then it goes back to cool. This happens on both a/c and just vent, so I'm pretty sure it's not specific to the a/c system. It also seems to stay hotter longer if I put the blower on the max setting. If I have it on max, it may go hot and stay hot until I turn it off and then back on. This is really aggravating and I am not sure what it could be or what to check first. If anyone has any idea what it could be or experienced the same thing, please help! I have read about the blend door being a problem but the way that this happens intermittantly has got me puzzeled.

I appreciate all the assistance!

 

check your blend door motor its a door that controls where the air flows under the dash

 

I am not sure how to check it but I plan to take the glove box out and see if I can see it.

I noticed when I drove it for lucnch today that it actually gets hot every 30-35 seconds. There is also a noise that comes from behind the glove box just before the air gets hot. It is consistent though... every 30-35 seconds, hot air for 3-4 seconds and thene back cool. I also heard the noise even if I turnded the fan completely off!?!? Why would it do that?

 

do you have any vacuum leaks under your dash area.

 

if it helps, it should be a small rectangular plastic box mounted under the glove box with 3 screws holding it up to the bottom of the big plastic housing. just be careful if you pull it off because it has a small metal collar that aligns it to the shaft of the damper door and the collar will come loose. It just pops back in place though.

 

Little update here and trying to see if this is a clue. The actuator opens and closes the blend door even when the vent **** is set to off. Is this normal? If not, what should I check?

 

OK, I'm interested now, as I just bought a 99 that may be doing the same thing. I have noticed some funkyness with the temperature but have not looked into it.

My only other dodge truck experiance was working on an 02 which had hot air on one side and cold on the other. A really great site was heatertreater.net. I talked with the owner and although I did not need to purchase a part from them their advice was used to solve the problem.

The blend door motor if anything like the 02, is a servo motor that is controlled by a pulse sent to it. I think your problem and mine may be from a bad HVAC control board. I will run a test tomorrow and see what mine is doing and see if I can find a cause.

you should email heatertreater.net and see if they are aware of this problem and if they know of a fix yet.

 

Sounds like a lot more work and $$$!

Im going to fire off an email to them shortly.

Let me know what you find and I will do the same.

Thanks.