How to trouble shoot the heating system of 1985 Carrera

[tshih]

My car, 1985 911, has lost heater controller. How does one check the sensor (between the sun-visors), the temperature sensors in the driver side exchanger and the location of another sensor? Also what about a service that repairs the circuit board (replacing a transistor by soldering in the new one?) in the central console under the heat controll dial.

Tom

[APKhaos]

What are the symptoms?
This system is well understood by quite a few of us who have exorcised various afflictions of the heating kind.

Random component swapping is not the best approach.Give us the specifics on what it is doing/not doing, and we may be able to help.

[tshih]

Tony,
the symptoms are turn on between seats dial to #1-7 no heat. When dial is on higher numbers you can heat a defroster motor kick in but still no heat. Manually take off the springs holding the flaps in heater valves under the car and heat comes on full (way too hot in winter!) must put vent controls to maximum influx of fresh air to moderate the heat (hot enough to toast feet). I feel the circuit board (which costs $450 from dealer may fix the problem) may be bad not actuating the levers that allow the duct flaps to open and let in the hot air from the heat exchangers. Do you know how to test the circuit board with a VOM or send it to someone who has done this before?

[LeeH]

Frequently it's the actuator arm that connects the servo to the cables. With the ignition on (engine off) listen closely around the heater control and you should be able to hear the servo running as you move from off to #7. If you do hear the servo running take off the hand brake boot and look inside with a flashlight. See if the small arm is attached to the servo on one end and the cables on the other. Those connectors didn't age well.

[Jim Smolka]

Also, to test the footwell blowers, the engine fan has to be running

[APKhaos]

Lee's tip is the hands down first thing to check.
Let us know.....

[tshih]

Thanks, I also found the other past threads posted by Will Ferch and John Walker about the plastic connectors which are easy to replace. Will take a look this weekend and let everyone know.

[c2 rower]

For a Carrera, when does the electric blower on the engine come on? When ignition is on or only when heat is on?

[Wil Ferch]

For my 85, the engine blower motor on y comes on when the auto heat dial is dialed-up very high ( highest, "9" setting?). It's supposed to come on also when the engine temp gets too high, without you doing anything.
---Wil Ferch

[tshih]

Guys,
I just looked inside the controller through the rubber boot of handbrake lever. There is a loss of attachment from the 4-5 inch long connecting rod (plastic fasteners are screwed into the ends of this rod) to the lever operating the wires to the exchangers's flaps in the heater boxes.

Anyone can post a parts diagram showing the mechanical routing of the heater system. Does removing the 4 allen head bolts permit the removal of the rectangular controller cover to get access to the wires actuating the flaps.

Lastly I tried turning the dial to actuate the arm which the connecting rod was attached to and while there was noise of motor and fans coming on the rod lever never moved. Is this the cause of my problem?

[APKhaos]

This has been done to death - plenty of detailed guidance in the archives.
For starters, try Auto heat troubleshooting
and Automatic heater control unit repaired -- 70 cents! has some great pics of the heater control unit mit zer rodden rods.

Yes, the four hex bolts hold the heater control unti cover to the tunnel. Remove the temp control knob from the top of the cover before you lift the cover.

[tshih]

Thanks Tony for the leads. The pictures posted on your links answers my question easily.

Will install the new bushings and lube the cables and flappers with WD40. Maybe change the springs at the flapper boxes to lower the force in pulling the flappers closed.

[APKhaos]

The spring tension helps overcome any cable stiction. The controller has tons of torque to handle the tension. I'd lubricate everything, but leave the stock springs.

[old_skul]

God forbid, don't use WD40. People on this board will shred you. Use 3-in-1 or some other non-smelly grease on the flappers.

(I used WD40 on mine, but don't tell anyone - shhh!)

[tshih]

Just to let everyone know what happened. I took the console apart to install the new plastic bushings and the heater works again. I didn't have a chance to use any lubricants under the car so the cable system is not binding (yet).

Many thanks for saving me $$$$$.

[APKhaos]

You are a king of the Carrera autoheat. Now, on to bigger conquests!
Whatever you tackle, the board has been there. So it!