Debugging all the problems with the heater

[karmannghia60]

Car is a 1979 SC
Heater doesn't work at all. No blower, no heat, nothing
Checked fuse, it's ok
Blower wires in the engine are connected
Pulled the unit apart
here are some pictures and comments

The knob doesn't move


Connecting the two yellow wires on the left doesn't do anything. I am assuming the blower should come on


There isn't any live wires except the red/while pointed to with the yellow arrow

The lever with the red arrow doesn't move by hand at all


Where on earth do I start with this mess??
Thanks
Rafik

[Tremelune]

It looks like you have "auto heat". It's somewhat rare. I don't know much about it, but that term should help in your research.

It sounds like your problem is electrical. The servo in your auto heat module isn't pulling on the cables to the flapper boxes that allow heat to pass to the front of the car or activating the relays that turn the blower(s) on to force that heat towards the flappers. I don't know much more about the module.

There is the option of replacing the auto heat with manual heat (handbrake assembly and cables).

[cmonref]

Good luck getting this straightened out!

In your first picture, you say the knob does not turn? It should, of course. It is the shaft of a rheostat that provided a variable resistance to the circuitry to modulate the heat.

Again on the first picture, that shaft should have a plastic piece that has a small arm on it. That small arm activates the small switches at dial=0 and dial=defrost (the two extremes of the dial's range.) At dial=0, the switch turns off the system so the heater control will go down and turn off the heat. At dial=defrost, the switch bypasses the interior sensor and turns the heat full ON -- lever full UP -- to provide the maximum heat. Between 0 and defrost, the potentiometer provides the variable resistance which the circuitry compares with the interior sensor (between the sun visors) which reports interior temperature, and the sensor in the driver's heater box (engine compartment) that reports whether the input air is, in fact, hot.

In the picture with wires, there is only one wire with power -- you correctly identified it. The two 2-wire connectors input the two sensors (interior between the sun visors, and in the driver's heat box.) The two brown (oops -- they are yellow) wires switch ON/OFF the fan in the left side of the engine compartment. That fan provides some constant airflow when the heater control is at least slightly up from full down.

In your third picture, you will NOT be able to move the actuating lever by hand. Or at least I can't move mine, and the unit works as it should.

With all that said, there is lots of information on the Board, available thru search on "Autoheat". Again, good luck.

If want to revert to manual, you will have to replace the special bolt that mounts the parking brake lever and the arrangement of frictions discs and washers that are mounted on the bolt. You do NOT have to replace the parking brake lever itself -- just the bolt and the discs that mount on it. Use a PET for your car, carefully catalog the bolt and its discs for both the autoheat and the manual systems, figure out the additional parts you need, and visit your dealer with a parts list. It has been 25 years, but as well as I can remember, it is about 10 different individual parts that you will need.

[Tremelune]

That doesn't make much sense to me. If there's a leak in the exchangers, it's getting into the air channel, regardless of whether or not the motor blower is pushing air in or the footwell blowers are sucking air out. Neither of these blowers would overcome the pressure of an exhaust leak.

[cmonref]

His car is a 911SC and does not have footwell blowers. The footwell blowers came with the later 3.2L Carreras.

[karmannghia60]

Correct, no footwell blowers
I did somemore digging, pulled the blower off and hooked it up directly to a 12v source, it worked
Then went to the rear fuse box. Fuse #1 (for the relay) has power. Fuse #2 (to the blower) has no power. But I can't see a replay at all. Not even a loose terminal for it
Does my car supposed to have a replay in the back?

[timmy2]

You are missing the rear defrost and blower motor relays on your rear fuse panel.

[karmannghia60]

Timmy2, yes but there isn't even terminals for them. That why I am asking if a '79 SC had them?

[karmannghia60]

Sorry, the picture was upside down

[pmax]

Kg60,

You are missing a standard black relay 911-615-109-01 here.

That's the SC heater blower relay

[karmannghia60]

Thanks pmax, that makes sense

[universeman]

I see your problem - the Haynes manual in the first pic.

:-)

My blower relay socket there is loose and the blower motor only works if it's pulled out slightly. When you put one in, make sure you jiggle it around a bit before you conclude that the problem is elsewhere.

[timmy2]

Timmy2, yes but there isn't even terminals for them. That why I am asking if a '79 SC had them?

The telay sockets are there. The black one loose by the remote VR should have a relay plugged in. Same as the rubber one already pointed out.

[Tremelune]

Is this the pricey reed relay? Surely there's a modern solution using standard components?

[pmax]

Originally Posted by 86 911 Targa

KG60,

This is not the relay you are looking for.

[86 911 Targa]

Originally Posted by pmax

KG60,

This is not the relay you are looking for.

This is a replacement suggestion for P/N 911-618-153-00

I deleted my other posts.

O.K., So what is the correct P/N for the 1979 SC Heater Controller Relay?

[karmannghia60]

911-615-109-01, I think

[86 911 Targa]

Originally Posted by karmannghia60

911-615-109-01, I think

^^^^^
Correct for the round relay socket.

The rectangular socket is the 6 pin rear window defroster.

G.

[pmax]

91161511500

[karmannghia60]

An update
The centre unit had a seized dial so I replaced it. Not the heater is working as it should. I can hear it pull the cables and the lever is moving up and down
The blower still not operational,, just waiting for the relay

Today, I spent most of the day figuring out the mess at the front. This thing needs a double degree to understand. Anyway, the front blower and levers are now working too
I reckon my first two tasks on this 911 (my very first 911) has been the most difficult, fixing the oil leaks from the ToD and the heater