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Discussion Starter #1
1994 Cougar, 109000 miles

I just put a new heater core in; took me and a friend all day, too. Got everything put back together with no leftover parts or screws. All wiring harnesses are plugged in, where they belong.

Now, with the engine warmed up, it's giving merely lukewarm heat out of the vents: floor, dash, and defroster. I thought it might be air in the lines, and had to add some coolant a time or two as the air worked its way out. But I'm still not getting real hot air in the cabin at all.

The vacuum lines look good; they're not loose or pinched.

This has manual heater controls, and I happened to notice there is no difference in air temp when I turn the knob between full cold or full hot. It blows only lukewarm air on any setting. I have a hunch it might be the blend door? Blend door actuator? Temperature blend switch? I'd rather not pull the dash again, but I will if I have to. So I'll start with the easy one first- Is there a way to test the switch? I see it has 3 wires on it.
 

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I was thinking about it and remembered-- when I pulled the heater core, there was a white plastic box just above it which I had to unscrew to take the core out. But instead of removing that box, I just took all but one screw out and twisted it out of the way (at the time I thought it was just a circuit board). I bet that box works the blend door and I must have tweaked it enough to make it fail.

I plan to pull the dash again (sigh) and see what is going on back there. If I need to replace something, I hope it's not expensive.
 

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I was thinking about it and remembered-- when I pulled the heater core, there was a white plastic box just above it which I had to unscrew to take the core out. But instead of removing that box, I just took all but one screw out and twisted it out of the way (at the time I thought it was just a circuit board). I bet that box works the blend door and I must have tweaked it enough to make it fail.

I plan to pull the dash again (sigh) and see what is going on back there. If I need to replace something, I hope it's not expensive.
http://forums.tccoa.com/showthread.php?t=93051&highlight=blend+door+fix

If you broke the blend door while doing that...

Try this and good luck

http://www.youtube.com/watch?v=3BVyZWpS7TM
 

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Discussion Starter #4
Oh, yikes. I really don't feel like cutting stuff apart. I may have lucked out, though...

Got it all pulled back apart- sure enough, it's the blend door actuator (F4SH-19E616-AA).

It seems that what happened is while I was putting things back together after installing the new heater core, that I put the actuator back without getting the actuator shaft in place to actually operate the door. I'm in the process of installing it the right way and hooking up enough things to verify operation.

I've got my fingers crossed.
 
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