Frying ! Bad heater control unit ?!

This is primarily an exasperation post,but i am looking for a way to avoid paying $ 1200 to Porsche dealer for a new heater control unit.

My story is I just bought a 1988 930, drove it home, and now after 30 minutes of driving the heater rages out of control - you can't turn it off. I took it to Porsche dealer - I am not a wrench unfortunately - and they say it needs a new (electronic) heater control unit for $ 1200 (new OEM price).

Two questions:
1) Can you recommend good used parts dealers (beyond PAP and Vertex whom i have contacted already)) for this part, and/or
2) Does anybody out there have one of these for sale reasonably ?

Any other fixes possible to shunt/circumvent this control scheme ?

Thank you, in advance

I have an idea that may work. The heater control between the seats is given a signal from your heat exchangers that determines the amount of heat flow. You can get rid of this automatic control feature by unscrewing the center control between the seats. There should be 2 different wires with connectors on the end plugged into the underside of this unit towards the front. Unplug these, this should circumvent the automatic function and allow you to manually adjust the heat.
Good Luck


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Dante Oliverio
86 Turbo-Look Cab

One more thing, If this option does not work, contact Ian's Euro Parts 954-968-3766
I have found he is the best parts place to deal with.

Buy a copy of Excellence Magasine. They have a TON of adds for dismantlers.

Adam Roseneck

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1978 911SC 3.0
roseneck@cyberbeach.net

I junked the auto heating system and installed the older, manual dual lever heater control system. I found a dual lever/e brake handle unit at a swap meet for $15 and had my mechanic make the retro-conversion for $100. (Dismantlers will have the item) The manual system is far superior to the auto system in that you can run hot air on the right side and more temperate air in the left footwell, thus not burning the soles of your shoes. I like being able to reach down between the seats to make small changes to the left and right side heat. More hands-on than the trouble-plagued auto system.
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Chuck
83SC

Hey patalive, thanks for the suggestion as I once had a Merc 300D with similar setup- very flexible and functional.

Can you give me a year range of 911s from which I could get a lever set for my '88 930 that would fitup properly? If I can get the parts in black and find a qualified mechanic, I will go this route.

Also, to atr911 and Oliver911, great suggestions and I will probably employ them all until this prob is fixed - thanks.

Please suggest other fixes if others have had similar problems.

Well - - off the top of my head - a SWAG - any 1978 thru 1989 manual heater control/e-brake handle unit should work fine. I suspect that earlier years may work as well but don't hold me to it. I know others on this board are more knowledgable than me and hopefully will chime in.
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Chuck

Find out what is wrong with the control unit - it might be repairable. After all, you don't want to fit VW-style levers if you don't have to!

Patalive:
What will I need for the conversion you performed ? Just tunnel cover and levers ? Cables ? Anything else ?

The existing fans/vents work fine as is. Do I need blower motor ?

Thank you.

Assuming the automatic heater box in the 930 is the same as in the SC, there are temp sensors in the heat exchangers and just above the rearview mirror. The problem with mine was a dirty connection with the inside temp sensor.

There is a pretty comprehensive troubleshooting chart in the Bentley manual (which helped me get mine working).

I am not going to type the whole chart, but here are the list of symptoms:

1. Temp control in position 1, control servo moves to max heat.

2. Control module regulates to max heat in defrost switch position only.

3. Too much heat, does not regulate correctly.

4. Too little heat, does not regulate correctly.

5. Control module not regulating.

In your case I am guessing it isn't 4 or 5, but if you post which one of the above applies, I will tell you what the chart says.

Tom
82 SC Coupe

To emcon5/Tom:
The problem I have is your option "3", as the heater just blasts heat uncontrollably after the engine heats up. No levers or center-tunnel position change affects this. During this condition, the defroster works as well.

How long did the Porsche guys look at it before they came up with their diagnosis?

According to the chart, this could be an open circuit in the heat exchanger temp sensor (check resistance of the wire going to it, 1.7Kohm) or the potentiometer (knob) is set incorrectly.

From what you describe, it doesn't sound like either. With the ignition on but engine off, if you turn the knob from off to 1, can you hear the servo working, and does the red lever start to move up? You should also hear the blower motor in the engine compartment kick on. You shouldn't be able to move the red lever, as it is connected to a servo motor in the control box (One of the problems with my heater was the rod making this connection had popped off). When the red lever moves up, it pulls 2 cables and closes the vents on the flapper boxes, so the hot air from the heat exchangers is piped into the cabin rather than to the outside world. These are supposed to be spring loaded open, so if you lose a cable, you won't cook. It possible that one or both of the flapper boxes has rusted shut, and/or the cables/spring are broken. If you look under the car, inside the rear wheels, you can see the boxes. You may need a mirror, but you should be able to see them. This is what they look like (shamelessly lifted from the Pelican tech article on replacing them)



If you turn the knob and nothing happens, you may be S.O.L., but I would think if this was the case you would have no heat at all.

My money is on a missing spring on one of your flapper boxes.

Tom