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Old 08-11-2019, 05:29 PM
Nicos Elias Nicos Elias is offline
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Default '73 ambulance heat

Last time I drove my '73 Superior Cadillac, super-hot air was blowing into the driver's area from the climate control, even when off. If I turned it on, it would blow harder, and it's like oven-hot. Moving the temp. dial didn't change anything. Very uncomfortable and possibly dangerous? How do I stop it?
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Old 08-11-2019, 06:21 PM
Peter Grave Peter Grave is offline
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The issue is probably a vacume hose on the Climate Control system somewhere. My 96 Limo you can;t shut the heat off no blower problem after searching now in the spring I bypass the heater by hooking the in and out hoses together this bypasses heater core. In your case I would pull the blower fuse and do the bypass on the heater hose trick. Then start tracing the vacume hoses looking for pinched unhooked or broken.
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Old 08-11-2019, 06:29 PM
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Bill Leverett Bill Leverett is offline
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I had the same sort of issue with my '73 Lifeliner. As Peter mentiond it's most likely a vacuum hose leak. These vacuum hoses control the blend of hot and cold air by opening/closing shutters in the system.

Having taken the dash apart on mine to fix some dash lights let me tell you that there is a multitude of vacuum hoses that come off a central point. If I recall correctly, something like 8 separate lines. If you are lucky it's just a hose that has come off and can be popped back on. If not, tracing a leak is a big job. Paul can give you some good advice on this. I'd be looking to replace all of the lines with new rubber. If you have a leak in oneline you'll likely develop leaks in the others.

Best of luck withthe fix.
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Old 08-11-2019, 10:48 PM
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John ED Renstrom John ED Renstrom is offline
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The shop manual has a decent flowchart that is a big help. Most people jump on the vacuum shut off valve but really it only closes when the system is on max air. A stuck flaper will do the same thing. Remember on this system the blower does not shut off. First place to check is under the hood the main vacuum line on the engine is a known problem. Next is the servos inside on the heater box. Some big foot is always knocking one of them off. Default mood is set for the system to go to defrost if the controller is bad. So if its just blowing hot air. Do as suggested First. It most likely the blend door unless your ac system is out of freon. As it uses heat and cold to give you the set temp.
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