Heater controller in engine compartment
 

Hi,

I have a non-functioning heating on my 3.2 from 1984. There are many good threads about this that I have read on the forum but I can't find the logic on the heater controller to the left in the engine compartment. I have opened up that controller and when I push the relay to the heater fan it starts working. So now I need to check if the controller or something else is broken.

The controller has following terminals;
1. From the speedometer
2. Ground
3. 12V from fuse in engine compartment
4. Signal out to the footwell blowers
5. 12V output to the heater fan (but not on my car :()
6. Same as 5
7. 12V from fuse
8. 12V from fuse
9. input from the auto heat, looks like this should have 12V when starter solenoid is on
10. Temp switch situated on engine on a difficult to reach position
11. From starter solenoid
12. 12V from fuse

As I understand it the heater fan has two functions;
1. Help to cool down the engine at low revs and thereby poor cooling from the big fan.
2. Spread some nice warm air to the coupe on chilly days (like in Sweden now)

The first point should likely be taken care of by the inputs 1 and 10 but what input takes care of the ventilation heat? 9 and 11 looks to have 12V only when starter motor is on so when normal running I think they are dead or is my wiring diagram wrong? I opened up the auto-heat box between the seats and it has 12V on the yellow cables when I start the engine but nothing after that.

/Magnus

You may find some help in these threads:
http://forums.pelicanparts.com/porsche-911-technical-forum/322675-heater-controller-circuit-again.html

http://forums.pelicanparts.com/porsche-911-technical-forum/258473-help-does-anyone-understand-footwell-blower-circuit.html#post2326680

Thanks, the first one was new to me. Still lacks the explanation on how the auto-heat set the fan. Perhaps a winter project now when it is time for the red beauty to go to winter sleep. I would bet terminal 10 provides ground to the relay, perhaps it goes on after the motor thermostat to the auto-heat?
/Magnus

Dived into this problem now and found a faulty relay on the circuit board (inside the control box marked 89 82 46 and 911.618.153.00). After changing the relay I checked the function and it is terminals 9, 10 and 11 that switches on and off this relay to the fan (terminals 5 and 6);
If 10 (motor warm) or 9 (connects to solenoid if the knob between the chairs is set to something above 0) is connected to ground the relay switches on but if terminal 11 is on 12V, like it is when solenoid is on, the fan stops.
/Magnus

Magnus, I just fixed the heating system on my '86 Cab. I have the manual heat control with the three position switch between the seats. My engine compartment blower was not coming on and this is the requirement for the two footwell blowers to come on. I disconnected the harness at the engine compartment blower first and measured at the harness to find out if it is the engine compartment blower that is bad. There was no voltage at the connector so I moved down to the relay (controller at the left hand side of the engine compartment under the plastic cover) and measured pins 5 and 6 to find out if there is voltage coming out of the relay (in case the wire harness to the engine compartment blower was bad), but there was no voltage.
Next I measure pins 12, 7, 8 and 3 going into the relay and found voltage on each of the pins, so the reason for my engine compartment blower not coming on was inside of the controller (relay) in the engine compartment. I took it out and opened it and found the contacts of the larger relay turning the engine compartment blower on and supplying voltage to the coil that closes the reed switch to turn the footwell blowers on were corroded. All I had to do was to clean the contacts with some fine sandpaper and now my heat is working great.

Juergen

Here is my thread on this:
http://forums.pelicanparts.com/porsche-911-technical-forum/388445-carrera-removing-engine-compartment-heater-blower.html

And in post #36 you'll see an alternative to replace the controller with 2 simple relays.

Then we had the same faulty relay Juergen. I got a new one from Conrad (3 Euro + freight) which works well now.
/Magnus

Magnus, can you give me the item number from Conrad? Next time I'm in Germany I pick one up.

Thanks,

Juergen