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Old 12-01-2010, 21:40   #1 (permalink)
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'98 Grand Marquis Heater Problem..

First off the A/C blows cold fine its just the heater thats not working as it should. It will work, sometimes randomly for a min then blow cold again. I have read on here about the blend door problems and I was wondering if I have the same issue or if its something else. I really don't want to remove the dash to fix this. I have replaced the thermostat. The hoses to the heater core are getting hot. The only thing that I think it could be is the control knob to switch between cold and heat doesnt seem to make any difference. I have heard that you should feel the change when you turn the knob and hear the door open etc. My wife also said that it used to get hot just to the side of the control knob but not it doesn't. Maybe it burned out? All the other doors seem to open and close when you switch between floor and vent etc because you can hear them. There is no leak from the core. Its getting cold here in the south and my wife is freezing her nips off so I need to get this heat problem fixed as soon as possible.
Any help would be appreciated. Thanks
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Old 12-02-2010, 09:57   #2 (permalink)
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Re: '98 Grand Marquis Heater Problem..

Listen to see if you can hear the blend door motor operate/ With the key on and the engine off, turn from cold to hot and listen for a short hum. Here's the diagram. It can be the control or the motor. It is manual control?

[IMG][/IMG]
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Old 12-05-2010, 12:30   #3 (permalink)
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Re: '98 Grand Marquis Heater Problem..

There is nothing whenI change from cold to hot. How do I know if its manual control? Im British and dont know much about these American cars :) Give me a Rover or Vauxhall any time...
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Old 12-05-2010, 13:50   #4 (permalink)
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Re: '98 Grand Marquis Heater Problem..

I just reread your original post and since it has knobs, it's the manual control. If you don't hear the slight hum sound, it's probably the blend door motor. It's mounted on top of the heater plenum and you have to remove the instrument panel to replace it. Just make sure fuse #5 under the dash is good. That's what runs it.
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Old 12-06-2010, 20:51   #5 (permalink)
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Re: '98 Grand Marquis Heater Problem..

Alright thanks I will check the fuse first then see where to go from there.
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