91 FLEETWOOD: Cold Heat
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 91 FLEETWOOD: Cold Heat in Past Cadillac Vehicle Discussion; My girlfriend drives a 1991 Fleetwood (FWD, 4.9L). Recently the heater quit working; even with the climate control set at ...
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    Slick Black Cadillac's Avatar
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    91 FLEETWOOD: Cold Heat

    My girlfriend drives a 1991 Fleetwood (FWD, 4.9L). Recently the heater quit working; even with the climate control set at 90 degrees all it blows is cold air. The A/C works fine but the heater had been slowly going out last year; I would like to fix it before winter rolls in. Could the heater core just be plugged? If so whats' the best way to flush it? - THANKS!!

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    Katshot's Avatar
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    Re: 91 FLEETWOOD: Cold Heat

    Yes it could be clogged. Check the heater hoses to be sure. One will be hot, one will be warm probably. If the core is ok, they will both be hot. If it's clogged, a radiator shop is the BEST betbut you can do it with a garden hose if you want. Just be careful, the core is NOT designed to handle the full line pressure that your garden hose and supply, you could rupture the core accidentally.

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    Re: 91 FLEETWOOD: Cold Heat

    Quote Originally Posted by Katshot
    Yes it could be clogged. Check the heater hoses to be sure. One will be hot, one will be warm probably. If the core is ok, they will both be hot. If it's clogged, a radiator shop is the BEST betbut you can do it with a garden hose if you want. Just be careful, the core is NOT designed to handle the full line pressure that your garden hose and supply, you could rupture the core accidentally.
    Thanks, I appreciate your insight Katshot.

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    Re: 91 FLEETWOOD: Cold Heat

    I read somewhere on www.caddyinfo.com that someone used like CLR stuff to get all the stuff out of there, and used positive and negative pressure to slosh it around..... Good idea..... I dont know, but it is my $.02......

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    Angstrom is offline Cadillac Owners Member
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    I went through a whole winter with out any heat. Brrrr!!!! I had the car in multiple times for repair at the GM dealership and they could never fix it. FInally, I ordered the service manual and started researching it myself. I found that there is a device under the dash that is a programmer for the heating system. It also controls a box through air tubes and electronics to open and close a door that mixes outside air with the heated air to control interior temperature. This box was defective and only selected fresh outside air. So up here in the great white North, it was a real problem. I bought a replacemnt at the wreckers for about $50 and it has been working fine ever since.

    Same car, 91 Fleetwood FWD.

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    Tailfin's Avatar
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    Re: 91 FLEETWOOD: Cold Heat

    Just thought I'd throw in another possibility if this issue isn't long dead.... The thermostat could just be stuck open (which would be cool because that's 6 bucks :coolgleam ). The little valve that opens and closes and allows hot water through to the core could also be stuck closed...or the vacuum hose attached to it could be malfunctioning. If it just needs replacing, it should be an easy find at a salvage yard.

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