Heat/air won't switch from defrost.. - Diesel Bombers



24 Valve 2nd Gen Dodge Cummins 98.5-02 Discussion of 24 Valve 5.9 Liter Dodge Cummins Diesels with VP44 Injection Pumps
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Old 05-03-2012, 07:42 PM
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Default Heat/air won't switch from defrost..

ok guys my trucks heat/ac won't switch from defrost when i turn my switch... Is it my plenum.. i haven't really checked out the vacuum lines too much but it is still hooked up over by the dipstick where i've had it come loose before... thanks guys...
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Old 05-03-2012, 07:47 PM
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mine did the same and it was a vacuum line. so id check again
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Old 05-05-2012, 04:49 PM
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Mine did the same thing, it is a vaccum line in the engine compartment more than likely. Mine was on the fire wall, on the turbo side. But your leak could be anywere... Check all your little black vaccum lines and you'll find it.
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Old 05-05-2012, 05:25 PM
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As the others stated, you have a vacuum leak. With lack of vacuum, the HVAC defaults to defrost. A very common failure point is the plastic vac line on the cruise control servo. You'll find it under the driver-side battery. Battery acid drips down directly on the line and eats a hole in it. Very hard to see, even when you are looking for it.......

Last edited by mrclean; 05-05-2012 at 05:28 PM.
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Old 05-08-2012, 07:51 AM
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Alright thanks.. i'll keep looking... wonder if my chiltons would have a vacuum line diagram>???
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