I have a 2001 2500 4X4. I need a little help troubleshooting a heater problem. With the A/C or vent turned to full cold I get hot air when sitting at a stop light with the brakes applied. I can get the heater to cold again by turning the control to off and then back to A/C or vent but the next time I brake the heat comes back. The only thing I know the two systems have in common is vacuum. Does anyone have a suggestion or idea where I should start to look?

 

Try checking the blend door-seems like this is a area that tends to fail offten

 

Do you hear your A/C cycling on and off constantly?

 

sounds like a vacuum problem, when u break u r pulling vacuum for the brakes. look for a broken line going from the pump too the ac controls, the rubber connection boots dry out and crack too. the blend door isnt a prob on the 2nd gens.

 

X2 -it sounds like a vac supply problem. When stopped not strong enough to keep the blend door in the proper position.

 

The blend door is electric, all the other mode actuators are vacuum. With the key on have a look with a flash lite under the dash up by the hump on the pax side, rotate the temp sel sw from hot to cold, you should see the blend door act rotate and move the door from hot to cold. This is the first thing to do as you may find your problem right there.

 

vacuum is not used on the brakes on a 2001, they use power steering pump pressure

 

Anyone ever get an answer to this. I am having the same problem.