heater/blower issues

jugwahn · 09-05-2011, 05:09 PM

Hi folks, I have a 79 SC that has just had the rear heater motor and hoses installed
(too cold on the way home from work at night without some heat). The problem I have is the guy who put it together for me has no idea of electricals and stopped when the mechanical bits were done. I am an electrician and think I might be able to get the heater running if anyone tell me how the heating works and where to find a wiring diagram for this? Both electric motors (front and rear) work if I put supply to them. Thank you.

timmy2 · timmy2's Garage

Wiring diagram is available on the site here.
Try this page and select the 78sc should be the same.
Pelican Parts - Porsche 911 Parts Listings & Diagrams

Have fun, I'm an electrician too and it takes a while to learn the flow diagram but it makes perfect sense after a while.
I printed the whole thing in color and taped the pages together, then stuck it on the wall for reference.

jugwahn · 09-05-2011, 06:07 PM

Thanks Tim much appreciated, I love this site

jugwahn · 09-05-2011, 06:52 PM

Thanks Tim I have the diagram and it makes sense. I still do not know how the heating is meant to operate. Any help would be great. Thank you.
Justin.

Porchcar guy · Porchcar guy's Garage

I bought a wiring schematic on ebay for my 79SC that is in color and simple to read as I am an electrical minus..No code just names for each item...loved this feature...Got it push pinned on the garage door to the house..Still don't understand all but it makes more sense to me now :=)

tcar · 08:31 PM

Quote:

Originally Posted by jugwahn

Hi folks, I have a 79 SC that has just had the rear heater motor and hoses installed

...I might be able to get the heater running if anyone tell me how the heating works...

Both electric motors (front and rear) work if I put supply to them. Thank you.

Do you mean, the 'front' motor in the trunk? That has nothing to do with heat. That's fresh air ventilation only. Operated from the dash.

Only the rear motor, in the engine compartment is the heater blower.

You turn on the heater blower by raising the red levers on the floor between the seats*. You should hear the blower running if you raise the levers.

Your car should have the wiring, including the plug for the rear blower... should be right next to the blower. There are different plugs for different years, all are 2 wires (brown is ground) you may need to swap plugs.

You might want to post a pic of your engine compartment overall and up by the blower motor... maybe we can help you find it.

If you have your glovebox owner's manual, it gives a good description of heater operation.

*Unless you have automatic heat, then you have a box with a dial on it that raises the levers under it.

jugwahn · 09-05-2011, 09:36 PM

Thanks tcar, you nailed it, there are two levers (left right?) and a dial.
I do not have the glove box manual, are they available?
I was told each of the motors work together and I really have no idea how fresh air or heat work as they were not operating when I bought the car.

I will post pictures if I need to and this probably won't be for a week (ahh).
I appreciate all you help,
Regards Justin

RedRoseRomer · 09-07-2011, 06:10 AM

I have an '81 SC (RHD) and the heater appears to be controlled by a dial in between the seats, from blue through to red in about 9 steps. But it doesn't appear to actually do anything.
Next to the handbrake lever is a red lever marked "DEFROST" and the handbook advises not to touch this (!), but why?
As I have tried all the other levers without getting any controllable heat, I have moved this red lever and it feels like it is moving an electric motor through a high gear, it moves very slowly.
Can anybody help with explaining the system, it will soon be winter!
Regards, David

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by jugwahn

Thanks tcar, you nailed it

Did the rear blower come on when you lifted the handles?

There are three separate systems. Fresh air, heat/defrost and AC.

I may have a few details wrong but the basics are:

Fresh air is assisted with a front blower. It dumps fresh air into the car through the center dash vent. I think that is about it on this system.

Heated air comes to either the driver or passenger footwell from under the dash. Dumps hot air down. Levers between the seats engage the rear blower motor and control the amount of hot air by cables connected to the heater boxes near where the engine and transmission meet. One heater box on each side. Air from the fan and hoses is pumped over the exhaust pipes and through ducting to the heater boxes. If the levers are not up hot air is dumped out onto the road. If you have no rear electric fan the big engine cooling fan will still supply plenty of hot air if the rear hoses are connected and the between the seat levers are up. Folks sometimes remove the blower fan and just hook up hoses direct to the exhaust for a cleaner looking engine compartment.

The heated air can be diverted to the windshield by a dash lever or mixed between defrost and under dash heat.

AC - Air is sucked into the passenger footwell - way down by where your feet are - and up through the AC evaporator in the smugglers box and dumped into the car through center vents UNDER the dash and out the two little tiny side dash vents. The AC blower fan is separate from the fresh air blower motor.

Sooo.....

A center fresh air fan
An AC blower fan in the smugglers box
A hot air blower in the engine compartment

There is also an AC condenser cooling fan in the nose of the car.

Later 3.2s had footwell blowers to assist the hot air blower in the engine compartment. The SC's don't have footwell blowers. This may be the info you heard about the front and rear fans.

Edit - I do not have a dial to control temp between the seats so I can't help you on that.

timmy2 · timmy2's Garage

Nice write up Bob.
Cleared up a few of my questions
It's nice to know that my SSI backdate won't affect my heat too much as long as my ducts are all tight and functioning correctly.
Thanks.

jugwahn · 09-10-2011, 07:07 PM

Thank you all for your help.
I have had to chase up some new hoses and a heater fan and now have heat in the car ( and how it operates) , which is great for those cold late nights. I have had to hurry home to avoid getting frozen, probably still have to hurry !

RedRoseRomer · 09-12-2011, 05:53 AM

I don't have AC on my car so that's one problem out of the way!

Think I'm happy with the fresh air system, the middle lever is the direction, the upper lever (and the fan switch) control the volume. But this only seems to come through the dash vents.

Heated air is controlled by the lower dash lever to either the screen or the footwell. Doesn't seem to be any volume control, though.

Having loosened the red lever between the seats, it now appears to be controlled by the dial, from hot to cool. Not sure what the mechanism is and I can't get it to go cold now, sometimes it is too warm even on the lowest setting. Still, it is nearly Winter!

Not sure if the rear fan is working but that doesn't seem to matter.

David