2nd Gen Non-Engine/Transmission Cabin Temperature Control

[jgallentine]

I have a 99 3500 extended cab and I think it needs a new reostat that controls the temperature of the air while on heat or AC.



If I have the AC on and turn the temperature knob all the way to cold I get ice cold air. As I turn the knob towards heat, nothing happens until I get almost half way around at which point the air goes from cold to quite warm. From there, if I keep turning the knob towards the hottest setting, the air keeps getting hotter as it should. If I then move it towards cold a couple notches at a time the air will gradually get cooler but about a 1/4 turn before getting all the way to the coldest setting, the air goes back to ice cold.



This control is working the same whether I am using heat, AC or vent. In fact, with the truck off you can hear the electric motor react as described when the knob is turned.



This issue seems to have coincided with the replacement of the AC evaporator core and the heater core. The only thing that could have impacted this is that I took the temperature control motor off of the duct/housing. Inside the plastics of the motor housing is actually a little electric motor. I could have put that back in up side down but I can't see whereas that would even make a difference. It is just an electric motor with two contacts and if this was a problem I would have expected the motor to think hot was cold and cold was hot.



My guess is a bad reostat/temperature control switch. Any other opinions or things it could be?



Thanks

 

[BDMiller]

I've never ripped into my Dodge's heating controls but on other vehicles I've owned the temperature is controlled by a vent that allows some air to go through the heater core & some to go through the AC or come from the outside. Maybe this is stuck? Frequently these are controlled by vacuum & a leak can cause all kinds of mayhem.

 

[jgallentine]

Brian,



Thanks for the input. On this model the temperature is controlled by a door within the duct work. However, the door is controlled by an electronic servo. The door will swing from full cold to full hot but it does not have any finite adjustment on the cool side. It goes from full cold and to pretty warm all in one swipe when the temperature control know gets about half way around and then I have finite control on the warm side. The other interesting this is that if I start oh the hot side, I have finite control all the way to cold.



Went to the dealer today and the control switch is $140 and they have never sold one. Of course the service department says there are just too many things to go wrong to even give any input as to what may be causing it but for $90 they'll check it out.

 

[BDMiller]

$140???



Whoah, is it made out of solid gold?



Any junkyards near you?

 

[jgallentine]

I didn't see solid gold in the list of features but you would think so at that price. There are a few boneyards around here but they are somewhat difficut to deal with. Having said that, looks like I will be trying to shop a few as in the absence of other inforamtion I think it has got to be a problem with the switch.

 

[DTangstrom]

Brian,



Thanks for the input. On this model the temperature is controlled by a door within the duct work. However, the door is controlled by an electronic servo. The door will swing from full cold to full hot but it does not have any finite adjustment on the cool side. It goes from full cold and to pretty warm all in one swipe when the temperature control know gets about half way around and then I have finite control on the warm side. The other interesting this is that if I start oh the hot side, I have finite control all the way to cold.



Went to the dealer today and the control switch is $140 and they have never sold one. Of course the service department says there are just too many things to go wrong to even give any input as to what may be causing it but for $90 they'll check it out.

After I did my evaporater this summer I did not have heat or AC. This was because I did not put the door back in the proper position. If you take that motor off the bottom of the heater core, it is located by the transmission hump, you might be able to grab the hinge rod and move the door position assuming that it is not bound up.

 

[jgallentine]

Yep, I had mine off as well. I really don't think it is in the door as it will go from full hot to full cold just no finite adjustment from full cold to warm about midway on the dial.