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85 Diplomat with A/C, won't shut off the heat...

Posted By: origcharger

85 Diplomat with A/C, won't shut off the heat... - 06/13/09 03:37 AM

Has A/C with automatic temperature control, have to clamp off a heater hose to shut off the heat
Under what circumstances is that vacuum operated valve supposed to close? Or is it a flapper door/control problem.
Posted By: In_The_Pink

Re: 85 Diplomat with A/C, won't shut off the heat... - 06/13/09 03:53 AM

My money is on a flapper door. If the setup is like F-bodies (and I think it is), all incoming air goes through the A/C evaporator first, then either through the heater core or bypasses the heater core.

Better look under the dash and check those vacuum lines.
Posted By: mod5v

Re: 85 Diplomat with A/C, won't shut off the heat... - 06/13/09 01:51 PM

If its like my 84 d150 it only shuts the valve in the heater hose on Max A/C and "OFF". other wise it lets hot water pass. I determined this by putting a vacuum gauge on the line that connects to the valve and running it in all positions.
Posted By: FuryUs

Re: 85 Diplomat with A/C, won't shut off the heat... - 06/13/09 02:46 PM

Quote:

If its like my 84 d150 it only shuts the valve in the heater hose on Max A/C and "OFF". other wise it lets hot water pass. I determined this by putting a vacuum gauge on the line that connects to the valve and running it in all positions.


Wife's Durango is the same way--I added a ball valve to the heater hose and turn it off in the summer to get NO HEAT.
Posted By: 70Duster360

Re: 85 Diplomat with A/C, won't shut off the heat... - 06/14/09 01:21 AM

mod5v is correct. The water valve only closes on max A/C. If you have heat all the time, then the servo motor for the blend air door is bad. I replaced quite a few of these in my days at the C/P house. I converted my old 5th Ave to a cable from an old (late 70s'?) LeBaron from the wrecking yard. Cost almost nothing compared to a new servo, which was more than the 5th was worth . Hope this helps!
Posted By: patrick

Re: 85 Diplomat with A/C, won't shut off the heat... - 06/15/09 11:38 AM

these cars also have a vaccuum fitting behind the controls that is prone to crumbling after 20 years....might be the culprit, too. of course, if that's the case, it should also default to just floor heat/cool
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