Automatic Heating Control Help?

[84porsche]

I did run a search and found a couple of good threads but didn't find exactly what I am looking for. I have the automatic heating control unit between the seats with 1-9 on the dial. The problem is the heat is always on. 450knotoffice helped me redirect the heat to the defroster so that it is not burning my feet. Please tell me about the system and please help me diagnose the problem.

Thanks.

[Mysterytrain]

My experience with autoheat is based on what I have read on this forum but he basics of the system are pretty much the same as the manual setup.
There are two damper boxes under the car. They are fed hot air from the heat exchangers. This is old VW technology with the dampers controlled by spring wire cables that run back into the car. On a manual heat system the cables are connected to a pair of levers with red knobs between the seats. Lifting the levers opens the dampers and allows the heated air to enter the car. With the levers down the dampers are closed and the heated air is dumped under the car. On cars with autoheat, the opening and closing of the dampers is via the 1-9 dial on the top of the heater console.The damper boxes [also known as flapper boxes] commonly rust and can be stuck in the open position. I would crawl under the car and have a look. Make sure they operate freely. There should also be a return spring on each one. If that all checks out then you need to examine the heater console linkage. There is a servomotor in the heater console box that operates the flapper boxes. You can access the control linkage via the side panel doors on the heater console...its easier if you remove the seat. The Bentley manual covers this stuff pretty well. Its common for the control arm from the servo to disconnect itself. I'm guessing if that was the case then the return springs on the flapper boxes would pull the dampers shut and dump the heat under the car...and you would have a no heat problem but with rust anything is possible.
As for the electronics, the fans have 3 speeds with the defrost setting is the fastest. There are also a couple of sensors to monitor or throttle the heat. One sensor is located on the driver's side flapper box. It's function is to prevent the heating system from operating until the heated air reaches a set temperature. The factory didn't want to blow cold air into the cockpit. The other sensor is mounted in the dash or above the rear view mirror and it monitors the temperature in the interior and sends that information to the heater console, allowing it to throttle the fans and flapper boxes to maintain the set temperature. Hope that helps.

[tonythetarga]

have a look at this thread: Auto Heater Problem

Under imcarther's reply, click the link under 'thread' and it opens up another string of conversation.

AUTOHEAT is the correct term to search for this system.

[84porsche]

THanks for your help so far. I will keep reading. Well I slide my camera under and this is what I found. They look pretty rusted to me.





I'll have to crawl under again when I have the car on jack stands to see if they freely work but it doesn't look like it.

[slodave]

From your pictures, those boxes are open, venting the hot air to the outside. If you are getting a lot of heat, I don't think the flapper boxes are the problem. BTW, in the pics, you should be able to move them by hand and close the boxes (rusty or not), the cable should flex enough. Inside the boxes, there is also a deflector that should close off the route to the front of the car. I suppose it is possible that this may have frozen in the position where it diverts air up front, even though the externals of the flapper boxes are venting outside.

Dave

[aj88cab]

It looks like the valves are not closed all the way. I believe the housing vent openings and outer baffle plate should line up more closely when completely closed. Look at the position of the inner baffle on the first photo, it isn't fully closed. If the servo is indeed in the closed positon and the linkage is connected properly, try loosening the heater cable clamping bolt on the heater box valves, move the valve to a completely closed position and tighten the cable bolt down.

While your in there.....it might be worth it to take off the valves and clean them up, paint them, and lube the shafts.

Good Luck
Andrew

[Mysterytrain]

The boxes look ok. One thing to note is that inside the box is a damper door. The door is what prevents the heat from entering the cabin. In your first picture, the driver's side flapper box, it appears that the damper is closed. That is also a good shot of the sensor.
Couple of things to check. Make sure the damper doors aren't rusted with sections missing. That would allow hot air to enter the cabin. Also, make sure that they are closing completely. It would take much of a leak to flow hot air into the cabin. They can be adjusted by loosen the nut that holds the spring wire captive. Use lots of wd-40 and be careful..you don't want to twist that rusted metal and have it break. Same goes if you decide to remove the flapper boxes completely and refurb. The mounting studs are welded to the body. Snapping one off can ruin your day.
Does the autoheat console function normally? fans come on? change speeds? Dampers open and close with the operation of the dial?

[450knotOffice]

bump.

[cmonref]

84Porsche:

Mysterytrain asks some good questions -- you haven't given us enough information about what is going on to use as the basis for a diagnosis. Try to answer these questions:

1. Does the autoheat control work? On ZERO, the levers should be FULL DOWN, on 10/DEFROST they should be full UP. In 'tween ZERO and DEFROST, the control should move the levers up and down based on temperature, your setting, and the temperature of the engine.

2. If the autoheat control moves the levers, do the flapper box valves move in concert? Two people are needed, one to operate the autoheat, one to watch the flapper valves move.

3. If the autoheat control moves the levers and the flapper box valves operate as they should, check adjustment of the flapper valves: autoheat levers DOWN -- flappers OPEN (as in your pix), and levers UP -- flappers CLOSED.

From your pix, it appears that the flapper box valves are moving. The pull wire has a cleaner look where it comes out of its guide tube, indicating that it is moving IN and OUT and rubbing on the rubber cap on the guide tube. That is a good thing.

Brian

[450knotOffice]

Chris' system in his '84 Carrera doesn't have any levers down there between the seats (my '84 with it's manual system does, btw). His uses a little motor in the console to move one lever located entirely within the console itself, hidden from view. This little lever is connected to both cables and hence both flapper valves. When he first got the car a few years ago he noted that the power plug within the console had been unplugged. He plugged it in and immediately noted that the heater fan on the engine began to run all the time. He didn't know that it wasn't supposed to so he left it that way.

Another thing with his car is that the temp sensor in the upper window frame between his sunshades was removed and has never been there for as long as Chris has owned the car. In fact, when we tried to find the wire that would have connected to the temp sensor up there, it wasn't there. That temp sensor needs to be there in order for the Automatic system to adjust the temperature as necessary.

Additionally, the lever that connects to the flapper valves, when disconnected from the electric motor, is still very, very difficult to move. There's no way that little electric motor could move that lever. The action is too stiff. So, no doubt the cables need to be replaced.

We jacked up the rear of the car and took a look under there. Everything looked fine. If you just grab the valves they move manually just fine. The flapper valves inside appear to be basically fully closed, maybe open 1 or 2 millimeters at most, which might account for the small amount of heat which actually makes it into the cabin irrespective of the valves being basically fully open to the atmosphere and dumping the majority of the heat overboard.

So what he seems to have here is :

1) No temp sensor
2) The heater fan is on at all times, even with the selector in the lowest position (that doesn't seem right to me. My manual system only turns on the fan if I pull up at least one lever. If the levers are full down on mine, the fan is not on)
3) The cables to the valves seem to be binding big time.
4) Possibly other things too

My suggestion to him was to junk the auto system and just find a used manual system like mine and install it in place of his overly complicated system. Has that been done here?

In the mean time, we unplugged the plug that was sending power to his heater fan at all times (basically to the way he found it when he bought the car) so it wouldn't constantly be pushing hot air through the small gap in heater valves and into his car.

[Mysterytrain]

Scott,
There is a lengthy posting that digs into the electronics and the theory on how and why the rear blower works and its relationship to the footwell blowers.

Help! Does anyone understand the footwell blower circuit?

Bottom line is that with the dampers closed hot air should not enter the cabin.
Manual operation of the lever [inside the control console] should easily open and close the flapper boxes.
Are the footwell blowers also running? can you change speeds?
It appears the system has been tampered with. The interior sensor is required. The link explains the operation of the engine compartment controller, the additional sensor on the engine and how the rear blower allows the footwell blowers to operate.

[450knotOffice]

Thanks for that Ron.

[slodave]

Scott,

Before Chris buys new cable, make sure that that the tubes where each cable comes out at the boxes, is not bent and rubbing against the outer vents (not sure what to call them). When I dropped my engine last year, I guess I hit one and the first time I pulled the levers, the right side stuck and had heat flowing at all times. A flat blade screw driver fixed that.

Anyway, the boxes should at least come out and get a good cleaning.