I just finished repairing a blown plenum gasket today...unfortunately, this was the second time in 9 months I've had to do it (I installed the Hughes kit in September, but like an idiot, I didn't use threadlocker on the plenum plate bolts and they backed out and the gasket failed....needless to say, I learned my lesson).


When I finished the repair this afternoon and I started the truck, it ran great, but I noticed that the temperature selector on the dash will not work. I am only getting AC right now. It worked before the repair, so I was thinking I had left a vacuum hose off somehow, since I actually had the exact same problem last time I had the intake off, and found a vacuum hose I had forgotten to reconnect. I have checked everything and could not find a loose hose or connection, however I did a vacuum test and got about 19" Hg. Is that a normal reading?


I was trying to burp the cooling system following my repair, so I had the radiator cap off and the heat turned on. However, the vents were only blowing lukewarm air, the AC clutch was running, and I noticed a lot of condensation dripping from the AC discharge tube under the truck.


So, my question is two-fold:


1) Is the temperature selector vacuum-controlled, or is it electrical? Is it possible my blend door just coincidentally gave up the ghost now, and the selector is actually working properly, but the blend door is routing the air across the AC coil?


2) My AC has also been acting up for quite some time - the AC clutch will randomly disengage for a while, and then if I turn off the AC for a while, it will usually work properly when I turn it on again. Is this likely a separate issue, or could it be related? It was a little low on refrigerant a few months ago, so I added some using a can of AC Pro I bought at my local parts store. The problem still persisted though.


Sorry for the lengthy post. Thanks in advance for any help!

 

Blend door on yours is powered by a little servo-motor under the heater box. It's just above the trans tunnel, towards the passenger side. There is a plastic coupler between the motor, and the axle for the door, that likes to crack, and it stops working properly. Do a search for "Heater Treater". It has nice pics and such on their website that details the problem, and the fix.

A/C problem is unrelated. You may still be low on refrigerant. If you still have the old can, and it has a gauge, put it on there, and see what your pressure looks like.

 

I took the truck for a drive tonight for the first time since my repair, and it appears that I may have just had some air in the coolant system, because the heat seemed to work fine. So that's good.


I did save a gauge from the AC charge bottle specifically in case I needed to check the pressure again in the future, so I'll do as you suggested and check the refrigerant level again next time it acts up.


Thanks a lot for your responses to my multiple posts recently, HeyYou! I really appreciate your help. This forum is such an incredible resource!


I will try to "pay it forward" by posting some links to some of my YouTube videos of the various repairs I've performed on my Ram to date....not as an effort to promote myself, but simply as a gesture of aid to others who need help. I'm working on editing the video from my intake manifold and plenum gasket repair, so when I'm finished with that I will try to post some links. I am by no means a professional mechanic...so my videos probably help as much to show the best way NOT to do a repair as they do to offer solutions...but, I guess something is better than nothing when you're a novice going into something blindly.


Thanks again to everyone that has helped me.