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Old 07-14-2012, 10:49 AM   #1
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Dash AC mode controlled by ???

Dash AC ????

2004 Newmar Kounty Star with Cat
The dash AC blows cold for 5-10 minutes after starting coach.

Then it looses all cold air, blows warm.

Is this hot/cold climate changing mode vacuum controlled with a vacuum operated hot water shut off valve like in many autos?

Four times under warranty Brandford, CT freightliner fixed the problem (billed F/liner thousands) and after leaving their facility the AC crapped out again entering the I-95 ramp 2 miles from their shop. I can't believe 18 wheelers would accept that crap on their long haul drives.

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Old 07-16-2012, 10:50 AM   #2
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In older rigs, like mine, the air temp when calling for heat is controlled by a water valve. The vent doors are controlled by a vacuum pump. Since your AC seems to be working, it sounds like you might have a vacuum valve failing, causing a vent door to close/open allowing heated air in.

Perhaps you have a split vacuum hose that opens when it gets warmed up, maybe it's in close proximity to something that heats up as you drive. Just looked at my setup and there are 3 vacuum hoses going to 3 valves to open and close distribution doors.

Since that one shop has had 3 chances to get it right and failed, shouldn't you try a different shop?

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Old 07-16-2012, 05:38 PM   #3
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I agree, rather than cycle the compressor on and off they often (in the case of "Factory Air" control the temp by running both the A/C and the heater, this greatly reduces humidity I might add, a good thing normally.

Your problem is the heater valve is stuck open, 10 minutes the engine heats up so it blows warm.
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Old 07-17-2012, 05:13 AM   #4
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Ditto on the heater water valve being stuck or not working. There should be a manual off/on valve in the hot water hose (not the return line) near the engine. It would normally be used as an emergency procedure should a heater hose spring a leak on the road. Some close it in the summer just to be sure no hot water (air) reaches the mixing valve.
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Old 07-17-2012, 07:50 AM   #5
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Clamp off the rubber hose that comes from the engine to the heater core. Warm it up and see if that stops the warm air. If so, heater control valve is leaking hot water. Easy fix is to put a shutoff ballcock on heater line. Close it in the summer.
2003 Newmar Kountry Star 3905, Freightliner XC chassis with CAT 330. Winnie the black lab, pretty Airbus captain wife, retired airline pilot with 11 grandkids. UH-1 pilot (Huey) U.S. Army 1967-1983. RVN 68-69. Northern Idaho my summer home.
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Old 07-17-2012, 08:03 AM   #6
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Welcome to irv2.
What you need is a ball valve or change out the Evans control unit.

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