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PatrickHenry 04-17-2013 08:47 AM

A/C Vent/Vacuum Problem
I'm having what would seem to be a vacuum related issue on my 2001 Ram 2500 with a 5.9 gas burner. With the A/C on, if I start pulling a hill it'll switch to the defrost. I had the same problem with my old ford f-150 that turned out to be the plastic vacuum lines crumbling and losing vacuum.

However, this seems to be a little different. I can stop, hold the brakes and put the pedal on the floor and there's no change. But from an idle in park I can push inward on the selector switch itself and replicate it. That's what has me puzzled, anyone have any ideas?

PatrickHenry 05-01-2013 09:47 AM

Wanted to give this a bump. Anyone???

lukc22 05-26-2013 02:49 PM

im having the same issue... hopefully some one can add something here

Warlock III 05-26-2013 04:24 PM

Check the plug on the thermal relay on the passenger's side floorboard. There should be 5 wires in the plug. If the plug/relay (not actually a "relay" but I can't think of what it's called right now) is bad it'll switch positions because it's electronically controlled.

440sp 06-02-2013 09:30 PM

Check the vac lines that are at the firewall on the passenger side there is a one way valve its hard to describe but those lines control the air doors for the heat and ac defroster etc........that's where I would look first they are prone to crack and the one way valve goes bad

Wh1t3nukle 06-05-2013 09:48 AM

This could be 1 of 2 things.

1. Blend door mount is broke

2. Vac line broke/detached

For number one, you can search on Youtube for my username and heater treater. Video shows what the blend door repair is after you buy the heater Treater part (search for that).

For number two, check your vac lines. An example I recently had a couple weeks ago was after a wheeling trip. I broke my red vac line at the front axle CAD. This caused the symptoms described with the A/C. Runs fine on level, but as soon as load on the engine (hill), defrost and not cold air.

Here is picture after I purchased replacement line and I added an extension. The break was at the union elbow on the CAD, red line.

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