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Old 11-07-2012, 04:01 PM   #1
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Warm Dash Air "Not Hot"

I have a 2006 QDP 42 Tiffin Allergo Bus. Live in NC, so not real cold weather. The Dash air is warm but not Hot. I know in years past in the Dump Truck Bus. on a Cat Eng. you could turn a valve on the Eng. to have warmer air. Not sure on the 400 Cummins. Can anyone tell me if this is possible to warm up the dash heat? Thanks NC

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Old 11-07-2012, 04:11 PM   #2
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Hello, I would think the air should be really hot just like in your auto's. The control valve that limits the hot coolant flow through the heater core might be opening fully.Try to locate that valve on your heater core hoses and see if it has a full range of travel when you turn the heat control up and down inside. Might have to have someone help you out so you can see what is going on. When you locate the heater hoses they should be hot enough that you won't hold your hand on them too long when engine is up to temp.

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Old 11-07-2012, 04:27 PM   #3
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There are several possible causes of "Warm but not hot" depending on the vehicle.

1: Thermostat (Engine t-stat) failed open, thus engine not reaching normal operating temp, thus heater not reaching normal operating temp. History: My girlfriends car on the coldest day in living memory had this problem.. I figured when I got to church it would be warmer inside... Wrong, Fr. is giving his state of the parish sermon "So thanks to Greyhound the boilers are paid for,,,, They don't work but they are paid for". FORTY BELOW your choice of F or C)

Second is a clogged or partially clogged heater core.

Next is a 2 parter, A: A faulty heater control valve not fully opening, (NOTE this may be caused by low air pressure or vacuum depending on the system) or "B" faulty air dam (A valve for the flow of air) same note.

Finally the air conditioner may be stuck on. (Clutch bearing siezed (happened to me) or short circuit)
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Old 11-07-2012, 04:54 PM   #4
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On my Cummins, there are two valves, one on top of the engine and one below. In times past I've had them either vibrate closed, or an engine tech purposely turn them off while doing work and then not turn them back on again.
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Old 11-07-2012, 05:13 PM   #5
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Also check the heater hose from front to back. There could be a pinch or a partial collapse in the hose especially where it goes over, under and around frame members. This could restrict the flow of engine coolant.
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