Getting cold here in Michigan and I want to get the automatic heater control unit working in my 86 930 which I believe is the same for all 911's 86 -89. This unit sits between the seats and has setting 1-9 with defrost.
Here's the problem, looks like the blowers just don't want to come on, I can fire them up seperately with direct power and I have already checked the heater valve servo-control rod and it moves correctly and is connected. Anyone have this problem before? Is it a bad circuit board? Part of the Servo control module itself? I get heat jsut no blowers (which I know are good?
Drew
86 930
89 C4

 

Some random thoughts:

Look under the car and see if the flapper valves are open. With the heater off, the flappers should dump all the heater output overboard.

With the ignition on, engine off, turn the ****. Does the unit make any noise? You should be able to hear the servo running, moving the arm.

If it does make noise, put the **** to max and wait until the servo shuts off. This should close the flappers completely, and direct all the heat to the cabin. Look under the car and see if the flapper valves are closed. I believe the valves are sprung open, so if the cable gets disconnected, the you will get no heat.

If all this checks out, check the condition of the hose connecting the heat exchanger to the flapper valve, and the hose on the other end of the HE's. On my SC, this is supplied by a blower, and by the engine fan. I don't know how it works on 930's, but it has to get air from somewhere.

If all this checks out, I really have no idea.

Tom

 

Check your sensor between the visors and disconnect and reconnect all your connections. My automatic heat control went berserk and started deciding that obviously I was too hot in the dead of winter, snow and ice about, 20 degree, but nothing like Michigan winters. Cruising along all windows closed, before the SSIs and the FVD muffler, its was quiet enough to hear the ominous click and whir of the motor driving the flappers open. Nothing I would do, pulling the sensor or rotating the nine position switch convinced the car that I really wanted heat. It was not until I returned home that it decided that I might need some heat. That was the end of that -- out with that POS, four allen bolts, electrical connections, and ball/socket disconnect. On/off switch for the fan, and little lever for the flapper doors. That circuit board is expensive!!

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

my '83 SC had the same prob. Finally after checking everything else, it turned out the sensor in the roof had a disconnected wire.
That has the effect of telling the heater unit you are too hot.
Bet that is the prob.

 

The servo control unit is working and rotates as it should. The hoses are connected and the cable to the servo is functioning to open the flappy door at the headers. It does get warm in the cockpit it's just that I have no fans... So it appears the sensors are working since I can see the servo control rod going to the appropriate postions for more heat as dictated by the position of the switch. Maybe the circuit board?? who knows??? I bought the new heater control unit off the Rennlist classifieds, we'll see if it works. Gotta be cheaper than buying just the circuit board, plus I'll have spare parts.
Drew

 

Fans? Bah. Just open the sunroof, heats the car right up.

Tom
(Nope, not kidding)

 

Does the electric engine fan respond to the switch position? The fan motor is garbage, one of the worst in the automotive industry and it lives in a rather tough environment. I assume that when you said the blowers are working, you are referring to the ones in the footwell; unfortunately they rely on conditioned air from the engine fan. I don't think those footwell fans are fused, but I recall seeing a recommendation to fuse those fans -- if you are jumpering direct to the fan you are bypassing a relay and possibly a fuse that a PO has installed.

 

Thanks for the sunroof tip, I'll have to go to that if I can't get this heater control functioning. As far as the engine fan, I don't hear any noises and to be honest with you is there even one there? This is a turbo and all I see is one big intercooler sitting were the fan normally is.
Drew

 

I went through all this last winter! I believe there's a relay in the fuse panel for the footwell blowers? did you check that? (I'm at work so I don't have my service manual with the schematics) The footwells also have their own fuse in the panel, I believe it's labeled "Auxillary Blower Motors" And my car had 10 amp in-line fuses right next to the motors (I'm sure you've seen those, since you tested the motors) So, see if any of that makes sense. If your automatic control is set to max, the footwells come on, so the relay that controls the footwell blowers should be energized.
good luck!
ell wente

 

I went through all this last winter! I believe there's a relay in the fuse panel for the footwell blowers? did you check that? (I'm at work so I don't have my service manual with the schematics) The footwells also have their own fuse in the panel, I believe it's labeled "Auxillary Blower Motors" And my car had 10 amp in-line fuses right next to the motors (I'm sure you've seen those, since you tested the motors) So, see if any of that makes sense. If your automatic control is set to max, the footwells come on, so the relay that controls the footwell blowers should be energized.
good luck!
ell wente

 

If the fans are working properly and the flapper boxes are functioning properly, it is probably the potentiometer in the control box. Check the archives for a proceedure to replace it.

 

Had same problem. It was the blower relay that was mentioned previously.

 

I am having the same trouble here in Chicago. Haven't figured it out yet on my 87 Targa, but heard that the engine motor is wired in with the footweel blowers - i.e., if it isn't working, they aren't working.

 

One other thing. When I had this problem, a couple of years ago now, we removed the unit that sits in the middle, it was dirty. Cleaned everything very well with wire brush, etc., hooked everything back up and it worked fine.

Just another avenue to explore while you're trouble shooting.

richard
'87 Carrera-3.6L (with heat)

 

I checked the archives on potentiometer replacement and found nothing? Anyone have any better luck?
Drew