78 SC ROW Autoheat question

[KiwiJohn]

I have owned my car for many years without bothering with using the heater much.
(Temperate climate here and not much winter driving)
It is now pretty much my daily driver and I have been trying to get the heater to work.
It is fitted with the autoheat console between the seats with a 9 position rotary dial and "DEF". The 7 to 9 numbers are in red.
I have just used the red lever beside the consule to provide heat, and it does get warm. Too warm sometimes, which means playing with the lever to go from one extreme to the other.
My question.
The engine compartment blower does not run with the red lever up.
Whatever switch turns this blower on seems to be in the servo mechanism itself.
If you pull the red lever up the connecting rod, lever to servo, comes off. I think it is designed to do this to avoid damage to the servo by preventing it from moving.
Short of a full overhaul of the autoheat electrics is there any simple way to get the engine compartment blower to run when using the heater manually?

[cmonref]

The engine compartment fan SHOULD run when the red heat lever is pulled up from the full down position. Check the two-wire connector at the engine compartment fan: one should have power with the ignition ON, and the other should be OPEN with the heating lever full DOWN and GROUND with the heating lever anywhere BUT full down.

[pete3799]

The fan on my 79 will not come on with just the lever up. You have to turn the knob to get the fan on.

[KiwiJohn]

Thank you ref...
I have no power or resistance change at the two wire connector as you describe.
I have the autoheat console out of the car so can see the red lever and its cable.
There is no switch visible.
Perhaps it is on the flapper box? Which I cant see with the car on the ground.

Thanks Pete....
Something to try that I had not thought of.

[cmonref]

I have no power or resistance change at the two wire connector as you describe.

The switch is not on the flapper -- it is inside the box and attached to the side of the emergency brake mount. (But there is a heat sensor in the output side of the driver's flapper that leads into the heater control box. The other sensor is overhead between the sun visors.)

Pull up the electrical diagrams on this board. The heater control and power circuits are on page 7 in traces 108 and 109. Turns out that the power lead is switched and goes thru the relay on the left rear electrical panel in the engine compartment. The ground wire should be easier to trace.

Good luck tracing the circuits.

[rattlsnak]

My Autoheat didn't work either and the rod popped off if you moved the lever just as you described. The lever is not supposed to be manually operated but I found that if you move it incredibly slow, it will work fine and not pop off. When you pull it up, you can feel the resistance in the servo. Just go really slow, and it should work. (as in it will take what seems like 3-4 minutes to get to the top. ) The only other way, is to replace the center unit with a manual type completely.

[pete3799]

I removed the rod entirely from the servo and lever and the lever works as it should. When I turn the knob you can hear the servo activate but it goes all the way on even if I just turn it on to #1 position. The sensor between the sun visors is missing and the sensor in the flapper box is also missing. I think I remember reading that the servo will go full on if either of the sensors is faulty.

[javadog]

The system won't work if you lack either of the sensors...

The red lever is only supposed to be used if the connecting rod on the servo fails. You have to hold it up manually, it won't stay up on it's own.

Test the two sensors, the values can be found in other threads here. If the sensors test good, you have a fault with the servo assembly and that neends to be troubleshooted.

You can remove the autoheat controller altogether and modify the lever to work manually. A few parts need to be changed but it's easy to figure out if you study the parts diagrams for a few minutes.

JR

[KiwiJohn]

Thank you all for the helpful suggestions.
I sure am learning plenty on the autoheat.
HOWEVER.
I seemed to have overlooked one important clue.



I think I am missing a relay.......... How embarrassing.
The square one is for rear window demist so the round socket I guess is for a
911 615 109 01 all purpose relay. Which hopefully puts me back in the warm air game.

I still can see no switch on the red lever.

[Bill Douglas]

The autoheat is pushing and pulling the levers (cables to the flapper boxes) so doesn't do anything that you can't do yourself with the levers. In other words a burst of 5,000 or 6,000rpm warms the car up in moments, and an autoheat isn't going to prevent that happening.

I'd just stick to the levers.

This is what I did to the autoheat in my '79SC.

[JSV798]

Check out this thread on auto heat

Auto heat Wiring

[KiwiJohn]

Thank you JSV for directing me to that old thread.
I too have been deep into the control unit, but I am not hopeful that I can get it to work.
Your identification of the yellow to brown wires for the rear blower and addition of a switch in this circuit will solve my problem nicely.

Just for interest, I found I could not drive the servo back to a position to attach the push rod without winding on the gear train.
Not exactly a Rolex, but pretty intense all the same.