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Heater and A/C switch flips back and forth


Visser's Avatar
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10-13-03, 04:06 PM   #1  
Heater and A/C switch flips back and forth

Hello all,
Hope someon can shed some light on my troubles.

I have a 1987 Mercury Grand Marquis Ls, with a 5.0 EFI engine with 140,000 mile and going strong.

One day last summer with the A/C on, I noticed that the car started b;lowing hot air. I thought it was time for a recharge, when it switched back to cool on it's own, and I then realized that there was a noise, (a "clunk"), coming from behind the temperature and A/C-Heater controls on the dash. (I know, I know....everyone hears a noise differently,a nd everyone wants to know what that "clunk" is...)LOL.. Anyway, out of instinct I would switch the temp gauge back and forth and when I would hear the "clunk", is when the temperature coming fromt he dash would change from cool to warm, and vice-versa. Then winter came, and the same problem continues in reverse. My car blows hot air and out of nowhere, I hear a "clunk" and the temp blows cold A/C. I've also noticed the temp changing back and forth when I accelerate heavy, and when I turn a sharp corner.

Am I nuts??

Anyone know what this could be? ( have a friend who believes it to be a "damper" behind the a/c controller, but I realize that this "damper" could be called a thousand other things, by thousands of other people. That may not even be the correct terminology for anything on a car.....

Bottom line, I know my way around a car a bit, and would like to repair this myself if possible. I know it would be easy to just bring it to a garage and pay to have them figure it out, but I'd rather save the few $$ if it turned out to be something simple.

Thanks,

Visser

 
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Visser's Avatar
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10-13-03, 10:44 PM   #2  
A little more info...

I took the A/C controller out of the dash to see if there was an obvious problem behind there. All I see are a number of electrical parts that I cannot identify, and they don't give any indication that anything is wrong. Thought I might see something mechanical not functioning. No luck.

I know this may not help much, but thought I'd mention it in the event it might.

Anyway, still looking for some thoughts if anyone has experienced anything similar.

Thanks,

Visser

 
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10-14-03, 04:17 AM   #3  
Joe_F
You mention that when you accelerate the temperature flips and you hear the clunking.

That's a vacuum problem most times. Get a good diagram of the A/C vacuum system from a shop manual or Alldata. Follow each line and check it closely. I think you'll find one split or missing/off.

That should solve the problem, barring any component failure.

 
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10-14-03, 09:07 AM   #4  
matm347
Yes, this does sound like it could be a vacuum issue, try getting on the highway and do some heavier acceleration(not floored as this will trigger the WOT switch and turn off the compressor), then let it coast.....if it "clunks" consistently then this reinforces the vacuum idea.

 
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10-14-03, 02:40 PM   #5  
Thanks for the input. I have a haynes manual on the vehicle, so I'll check it out and let you know what I find.

 
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10-15-03, 07:48 AM   #6  
Joe_F
Let us know the resolution.

 
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