Automatic heater control unit out on 79 911sc help!!
 

I have a 79 SC and just replaced the engine compartment heater blower with a Grainger motor, started her up and no go. I hooked 12V up and found that the motor works fine. Next step I took apart automatic Heater control unit and found a bent heater control stud/linkage ( the thing with the two ball joints on either end that connects to the red lever and the unit). I am not sure if it is supposed to be strait or bent to fit around the components but it was off on the floor. Further investigation I noticed that the circuit board was fried. So I took that out. I then connected the thing back up with the arm on the unit at full heat (used plier to move it all the way counter clock wise, VERY hard to move and could veel gears inside slowly moving, could be normal operation or that is why the metel linkage with the ball joints got bent?) Once I pluged the two brown wires at the back of the unit up I heard the rear motor go on!! So that is good news, bad news is there is nothing blowing in the car whatsoever and I heard no other motors go on under the dash, I did have the heater lever on dash all the way to the right.

So here are my questions.

1. Should I just buy a complete new unit on ebay for 4-500?

2. Can I fix it by buying a new circuit board ($200) and two new ball joints and straitening the linkage arm.

3. Will #2 fix the front blowers to the feet??

4. Should the linkage thing be bent or strait??

Please help!!!!http://forums.pelicanparts.com/uploa...1374896007.jpg
http://forums.pelicanparts.com/uploa...1374896022.jpg

Well the linkage should definitely be straight. I had mine out last year when I restored my interior.

There is a good thread on here about troubleshooting the autoheat and the footwell blowers. Do a search and you should find it. Lots of good info on process of elimination.

I think the short answer to your question is that if everything else is working with the autoheat unit, the footwell blowers should work also. There could be other reasons that the footwell blowers don't work though.

So the question is $200 on the board or $400 for everything. If you think the servo motor is working it might be worth the risk on just the board. Tough call. It's a calculated risk.

I've thought about backdating to the levers on mine, mostly because the 0-9 scale is misleading. It seems to actually work like this:

0, off
1-8, do nothing
9, open the gates of hell

I thought that bent thing looked fishy... I am thinking circuit bord and rolling dice. If the blowe worked when I hot wired it from the Control unit at least the wires are not fried from the unit to the blower in the engine compartment.

Thanks for your info, I am a newbie and need the help!!

Are there footwell blowers in a '79?
I thought they came later.

You tell me?

Not according to my service manuals... :)

Ok, that makes me feel better, no front blowers. So the question is if I change my circuit board, straighten my linkage (already did) buy new ball sockets and put er all together, think it will work??

Is your Autoheat the type with a red lever? if so somebody has probably forced it up at some time and bent the rod. The lever is an emergency option if your Autoheat stops working (which they do apparently) but you are meant to disconnect it from the lever thats connected to the Autoheat motor ( there is a small screw holding them together) of course its not that obvious until you read the manual.

I have a 78 SC and my fan and Autoheat were working but the rod had popped off (me forcing it before reading the manual), when i took it apart to put the rod back on and the fan and motor stopped working?

So i'll be following your progress with hope:)