Author Topic: Hot air all the time  (Read 1107 times)

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Offline mach1mustang351

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Hot air all the time
« on: August 23, 2012, 01:05:33 AM »
Team.  I have hot air coming through my vents at all time.  I suspect a bad heater control valve. Anyone else have this problem??

1987 AMC Wagon 4.0L, 3" Body lift, AX15, NP242
1981 AMC SX4 Sport
1969 Mustang (A Mach 1 with a 351)
1973 GMC K2500
2007 Suzuki Vstrom

Offline mechanic80

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Re: Hot air all the time
« Reply #1 on: August 23, 2012, 07:05:56 AM »
I have hot air at the vents too, (if the mode door isn't closed) but I replaced the heater valve with a a non-a/c valve because of the cost.  The valves  are physically identical (to all outward appearances) and the diaphragm does stop the flow of coolant.  I think it's the fact that hot coolant gets to the valve and the rest of the heater and valve gets hot because of, what's the word, convection? The A/C system does not have a charge and I'd like to get it working again, but the cost is prohibitive for now.  :amc:
Just because you're paranoid doesn't mean everyone's  NOT out to get you! :amc:

Offline Eagleearl

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Re: Hot air all the time
« Reply #2 on: August 23, 2012, 08:36:34 AM »
The shutoff valve should have vacuum to it when the control is on A/C. If it does and the valve is not shutting off there is something wrong with the valve. It may be stuck and you can move it back and forth to loosen it up or the diaphragm may be leaking. If you have the control lever on cool the flapper door in the heater core box should shut off the air flow through the heater core and let cool air flow through.

Offline BenM

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Re: Hot air all the time
« Reply #3 on: August 23, 2012, 03:28:46 PM »
Heater control valves are normally open (they allow water to the heater core) and close with vacuum applied. I have found four styles available. Three are metal, two similar for the six and one for the AMC 150 that has several bends. These three are generally priced at $80-$100.

The forth style is specified for Jeep Cherokees through 1998 and is plastic, after that Chrysler simply dropped the part and allowed the heater core to remain in the loop at all times. The plastic part does age faster, and there are common complaints of it weeping from the valve, but the big advantage is that it is available for under $20 at any parts store.

The Cherokee part has four 5/8 nipples, I think that the metal ones have 3/4 on one side.

1987 AMC Eagle Sedan -- 1976 Pacer Coupe -- 1968 Pontiac Tempest Custom S -- 1940 Mercury (& a 2002 Jetta Turbodiesel, 5 spd., the Wife's Daily Driver)