Heat problem help needed - 93 Mercury Grand Marquis

My heater stopped working last spring. A/C, blower, floor/vent/defrost, recirculate & outside air functions all work just fine. I cannot get heat to come out. If my limited information is right, the heater core has no valve to stop or limit coolant flow; the heated air is controled by air flow dampers (allowing air through the heater core or bypassing it). If this is correct, then it would seem that the actuator(s) controlling the air flow around/through the heater core aren't working. I have the standard heat-a/c with sliding hot/cold control, no climate control.

What is the layout of the heat control (coolant valve or just air ducting)? Where is the heated air / outside air damper (vacuum-operated) actuator?

Here's what I've found/troubleshot:

- when it first started having problems, the temp of air would 'stick' in hot or cold regardless the position of the slider. when cold, i would move the slider to hot, try banging on the dash, wiggling wires/vacuum lines, etc to get it to switch. once in a while this seemingly worked. mostly it seemed to switch over after some different driving styles (I assumed it was high vacuum states that got it to switch)

- Cold/Hot slider is a potentiometer, and reads ok with an ohm meter(~200K end to end, and the slider seems linear). It connected to a 10-12 pin connector, which went to ???

- disconnected the vacuum line header from the side of the dash heater control unit, and applied vacuum to each line to discover their functions. found defrost, outside/recirc, vent, vacuum source, but the fifth didn't seem to do anything i could detect. maybe that is the heater core damper, and the actuator is bad?

If I could locate the hot/cold air flow vacuum actuator, and if connecting my hand vacuum pump or an engine vacuum line (maybe with a manual valve) would cause it to operate & supply heat, i could live with that until i get more info or fully diagnose it.

Any help would be appreciated. Thank you, John

Reply to
John
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The temperature blend door on your Grand Marquis is an electronic servo motor, it's buried deep under the dash and a real pain to get to. Price new from Ford isn't too astronomical but figure 4-6 labor hours to replace.

Your symptoms are exactly the same as what I had on my 93 Crown Vic 3 1/2 years ago (intermittant operation followed by total non-response), if it makes you feel better, I changed the temp door servo while in a wheelchair, so, yes, it is doable.

Reply to
Neil Nelson

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