servo for automatic heat will not stop...

yngwie1 · 03-01-2007, 04:44 PM

Okay, here is what is happening:

I turn the car on and with the heater control knob to the off position I hear a constant operation of the servos. More specifically It pulses as if it is moving one way and then the other. If I turn the heat knob to say 5 or greater, it goes away and seems to work as normal. So, my options are to run the heat at 5+ indefinitely or wear out servos b/c it just won't turn off in the off position. Why is it not turning off?

Please help!!! :-)

Thanks,
Patrick

Cooper911SC · 03-01-2007, 05:01 PM

What car? 964? Just had to replace the control unit in my wife's 993. The fans just stayed on high regardless of fan control knob position or whether the ignition was on or not. She pulled the fuse to avoid a dead battery or burnt out fan motors. None of the other controls worked either. (Heat, A/C, etc)

More info please. =)

01sport · 03-01-2007, 05:11 PM

What year is your 911?

yngwie1 · 03-01-2007, 07:09 PM

Quote:

Originally posted by 01sport
What year is your 911?

Sorry, it is a 1987 911. Any help is appreciated.

yngwie1 · 03-02-2007, 05:22 PM

Anybody know?

yngwie1 · 03-03-2007, 08:32 PM

Still no suggestions?

Mysterytrain · 05:09 AM

I'm a bit green on the autoheat system but I can try to push you in the right direction for troubleshooting your system. My first thought when I read your post was that there is a problem with the sensors. There are 2 one in the cabin and one located under the car in the driver's side heater flapper box. The one in the flapper prevents the system from operating until the heated air is hot enough. The one in cabin is located between the sun visors or on the dash, on the right, between the steering wheel and the fresh air controls. It appears as a slotted bezel. Anyway, the interior sensor is the one that actually controls the inside temperature by cycling the autoheat off and on.
You are going to have to do some digging into the system. The Bentley for your year car would be very helpful and the $80 will seem very reasonable once you start the dig.
You will most likely need to remove one or both of your seats so you will have some access to the autoheat box.
The interior sensor should read 1.9k ohms @ 68 degrees.
The temperature control potentiometer might be out of calibration. Set the switch to positon 5. Remove the knob and adjust the the center trim screw so that the resistance between the soldered wire connections on the underside of the pot measures 950 ohms + or - 20 ohms. You might have a dead spot on the pot where it is set now. Sometimes by excercising the pot you can get it to clean the crud off... maybe some contact cleaner but it does appear to be a sealed unit.
The exterior sensor should measure 1.7 k ohms @ 68 degrees.
As you can see you need to pull the center heat console to make these 3 measurements.
auto-heater cooking me

hope this helps

yngwie1 · 03-04-2007, 11:12 AM

Thanks Ron, this gives me something to go on.

imcarthur · imcarthur's Garage

I agree with Ron. It sounds like the interior sensor. In my cab, the servo works overtime when I have the top down - due to fluctuating temps. But top up it cycles as normal.

Ian

Mysterytrain · 03-04-2007, 01:13 PM

Pat, one other thing. I have to assume that autoheat has a microswitch that turns the system on when you turn the dial on the top of the unit. That switch might also be defective [ as in fused on ] or it might be out of adjustment creating an always on condition. Seems like two issues..no off and hunting.

yngwie1 · 03-04-2007, 03:00 PM

Quote:

Originally posted by Mysterytrain
Pat, one other thing. I have to assume that autoheat has a microswitch that turns the system on when you turn the dial on the top of the unit. That switch might also be defective [ as in fused on ] or it might be out of adjustment creating an always on condition. Seems like two issues..no off and hunting.

Thanks again Ron. If only you were in Alabama and not Jersey I'd pull out the beers and we'd get this knocked out in 1/2 an hour. As it is though, your help has at least encouraged me to grab the Bentley manual and get out into the garage on this one.

Patrick

vintage guy · 08-22-2008, 01:49 PM

Patrick.....I know this is late and you are hopefully long past having your problem solved but this thread caught my eye since I had exactly the same problem you described. In my case I have figured out what was going on so I thought I would pass it along to future generations.

I have been going through the ailing auto heating system in my '87 and now have all 3 heater blowers working correctly but then the same pulsing of the servo motor surfaced. My flappers were not moving at all regardless of the position of the rotary heater control. After removing the access panel on the passenger side of the center console, I could feel that the actuating rod from the servo had broken loose from its attachment to the flapper cables. The loose end had fallen and was wedged so that the servo could not move its full travel. I rotated the heater knob CW so the servo moved and I could lift the rod free which then allowed the servo to move fully. The pulsing is now gone.

I will be pulling out the passenger seat to gain better access and remove the console. I suspect that I will need to free up the cables to the flappers and then reattach the actuating rod. While in there I will check for the proper resistance of the sensors and the pot. Hopefully I will then be home free and perhaps have one of the few properly working auto heaters in existence.

Wil Ferch · 08-22-2008, 07:23 PM

The attaching rods have a later, improved plastic ball joint that can be purchased separately... a bit tougher to install and "snap" in place, but better.

ludwig38 · ludwig38's Garage

Wil,
Can you tell me were you got that new rod for the servo?
(auto heat)
Thanks.
Rick

Mitch Leland · Mitch Leland's Garage

Sorry for jumping in on this, hooooRaaaah for Ron of MysteryTrain he's the first person that seems to know anything about the auto heat system for our cars. I've read Bentley's and it doesn't seem to cover the subject very well.

1. At what number setting on the console dial should the flapper valves be all the way closed?

2. What would be involved if I wanted to move the cabin sensor from between the visors down to the dash on my "84"?

Thanks,

Wil Ferch · 09-28-2008, 11:53 AM

The new rod is the latest updated part number from Porsche or from here at Pelican. It's identifying feature is that its a plastic socket all the way around...and snaps over ( with some force) on the metal ball. The old design socket is ( As I recall) a ratcheting type socket with a clasp...not one piece.....weaker.

The end-sockets are screwed on the metal rod...so set it at a ball-to-ball centerline length of 118 mm ( +/- 2 mm). If you have it , see p. 801-3 of the Bentley manual.

ludwig38 · ludwig38's Garage

Wil,
Can you supply the part # for Pelican on the rod please?
Thanks.