auto heat

[Nuen Werke]

Anyone know what causes the footwell blowers to come on normally but quit after 10 to 20 seconds?

[Speedy Squirrel]

The interior temp sensor is sends a target temp to the automatic control. It compares that to the dial setting. If they are equal the footwell blowers turn off. That is the simplified description.

[JFairman]

My autoheat box was doing something like that five years ago so I took it apart and looked inside.
First, it's an over engineered piece of crap and the old hand lever system was much better and worked great. It's worth backdating to the 70's hand lever system when the autoheat box goes bad.

Anyway, the geared down servo motor that slowly pulls the cables to open the diverter valves that send hot air from the heat exchangers through tubes in the left and right longitudinals to the footwell blowers also turns a steel cam wheel with a tang that trips a microswitch that turns on the footwell blowers.
The tang can be bent and that changes when the blowers come on.
I've forgotten everything I did but I bent the tang a little and now it works better. Before I did that the footwell blowers took a really long time to come on and now they come on right away when I turn the knob all the way clockwise.

There's more to it but I have heat when I want it now and turning the knob counter clockwise in steps slows down the blower fans.
Sometimes it gets chilly in S. Florida and it's nice to have heat.

[krasuskyp]

ugh - my heat is fuxor'd... its remedy remains on my perpetually growing never progressing to-do list

stooped ball joint busted under the knob, replaced and adjusted per spec but it keeps popping off

melted / busted one of the cables, have new pair to install

I'm sure there's more

any idea on what's involved (cost / effort / parts avail) in backdating?

I need heat here in fookin CT...

(sorryish for the TJ!)

[JFairman]

I havn't backdated to the lever system but Frank has and his works smooth and great. He did a nice job installing it. Cost isn't much because you use the same cables that are already in the car.
You see them in the classifieds every now and then. Some look crappy and the red knobs on the levers are bleached out from the sun and others are almost like new.
Some of them have the nice hand throttle lever with round black knob on the left side that has a plastic and still available new linkage piece that operates the throttle linkage rod in the center tunnel and the red knob heat lever(s) on the right side.
There's different ones from different years and I've seen them for sale on the classifieds from around $30 on up to around $100 depending how nice they are.

I would have backdated it by now but mine still works after modifying it. From the thick folder of receipts I got with my car the previous owner paid around $800 for a new auto heat box around 9 years ago.

[5.7 GT1]

I back dated mine, super easy. I purchased an e-brake interior lever with the heat control levers from a 76 911. It bolts right in. You will need to replace the two cables. I also purchased new red plastic lever ends and a new rubber boot from our host. Less than $100 and a few hours time all in.

[Nuen Werke]

Thanks fellas. I am going to check Jim's suggestion today.

[krasuskyp]

Thanks fellas too for sharing those details - sounds encouraging!

My auto heat worked great, when it worked. Then a flapper got stuck open and blazed heat always on. Then the ball thingy popped. Then the cable fried.

I'll keep an eye out for bits.

Jimbo... what's the hand throttle? Literally like a plane? Which cars had that - and why? Cold start idle? Neat!

[krasuskyp]

sorry for further TJ:

Any idea what $$$ I could reasonably ask for the e-control box? $800 new... $500? Just querious...

[Ronnie's.930]

Originally Posted by krasuskyp

sorry for further TJ:

Any idea what $$$ I could reasonably ask for the e-control box? $800 new... $500? Just querious...

Keep dreaming, buddy boy!

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[krasuskyp]

gee I guess I coulda shoulda done that - trying to do too many things @ once whilst @ werk 8-/

I wasn't that far off... still pretty valuable...

thanks

[JFairman]

"what's the hand throttle? Literally like a plane? Which cars had that - and why? Cold start idle? Neat!"
It was for a higher idle during cold starts. Some people may occasionally use it like a manual cruise control during highway driving on flat road if they get a leg cramp.
I've never liked cruise control because I feel seperated from the driving experience and not in as much control of the car.

edit: Hand throttles were in the early seventies 911's, I don't know when they started and stopped putting them in. There were a couple different types. One was on the left side of the emergency brake lever and another was farther forward on the tunnel where a center console would be on later cars. You would have to lean forward to reach it so the one on the left side of the emergency brake lever seems nicer.

The later 9 position knob servo motor auto heat boxes may be discontinued, I couldn't find one on pelican parts but I know they used to have them.. so you could probably make some money by backdating to the emergency brake handle with heater levers and selling it to someone wanting one if it's in nice condition and working right.
It does look like you need to replace the cables to the diverter valves when backdating to the levers. They're about $12 each.

Here's another 9 position one on ebay.
http://www.ebay.com/itm/Porsche-911-Heat-Control-Unit-/161196628612?_trksid=p2054897.l4275

[Speedy Squirrel]

There are people who fix the board, servo, and micro switches. Check the 911 board.

The point of my original post was that it is normal for the footwell blowers to switch off after a short time, depending on the dial setting. It is trying to control the temperature to the set point. If you want them on all the time, you turn the dial to the right.

The ball and sockets are a breakaway design. Once they break away they will not stay on if reattached. They break away because the pull wires are getting too hard to pull.

[JFairman]

If the cable needs lube go to a motorcycle shop and buy a throttle cable oiler. They fit over and clamp on to the end of the cable and you tighten down a little thumb screw to squeeze the rubber seal around the cable and then insert the plastic straw from a spray lube puff can into a little hole in the rubber part and squirt lube into it and through the cable. lube will go all the way through and shoot out the other end of the cable sheath cleaning and lubing the cable.
Or replace the cable, maybe thats easier and better.

Then jack up the back of the car and spray lube the diverter valves if they are dirty, rusted, dry, and stuck. The foam seal around the edge of the butterfly valves in them dry rots and goes away but they still work well on my '87.

[timspu]

i had a similar issue, when selecting the window defrost setting max hot the footwell blowers would come on and then switch off once the aft heater valves had fully opened and the motor in the heat controller went to max travel. In my case it appeared the heat control unit was wired incorrectly. The micro switches were wired the opposite way round. When the motor control arm depressed the microswitch this removed 12volts and switched off the blowers instead of keeping 12 volts to power the blowers. i swapped the wire onto the next terminal on the microswitch and it all works fine.

[Nuen Werke]

Well...tried Jim's suggestion and it the FW blowers came on for about 45 seconds this time and then went back to their slumber. Man, I am seriously considering a backdate

[JFairman]

It's been 5 or 6 years since I changed things inside the auto heat controller and I've forgotten everything I did to make the blower fans stay on. Part of getting old I guess.

Go back into it and while turning on the autoheat watch the servo motor turn the inside thing that pulls the cable and watch the microswitches being triggered by it.

Try tripping the micros witches with a finger or whatever to see what you need to do to them to make the fans stay on. It can be done and the poster above changed some wires around on one of them to do it.
You just have to experiment until you find what works.

I kind of wanted to keep the box because I mounted my MSD boost retard knob on top of the box where it's easy to get to while driving if I hear traces of detonation and a couple flush mount rocker switches in the side of it to do other things.

good luck with it.

[Nuen Werke]

Thanks Jim, back in there I go!

[Miguel Antonett]

Easy solution... the "automatic" controller is connected to the flapers lever via a 4mm short bolt in such way when the controller goes up or down it takes the lever with it adjusting the flow to the cabin. Take the 4mm bolt off and you can adjust the flapers lever manually regardless what the controller does. BTW, the controller sensor - located above the rear view mirror - has a diode (auto heat) that goes bad with time and is NLA.

[JFairman]

The original poster hasn't said what year his car is.

FWIW, the late eightees cars have the interior temp sensor for the auto heat mounted on the back of the ashtray frame. There is a tiny fan inside it that pulls interior air in through a clear PVC hose that is attached to a small round slotted vent on the lower dash to the right of the steering column.

I snapped the round vent out from behind and using a short piece of 3/4" heater hose as a spacer I mounted a 911 fog light switch in that hole to turn on my WMI. Looks original and works great.
The auto heat sensor minus the PVC hose now takes it's interior air temp readings from behind the ashtray and it still works fine too.

For those that have a late eightees 930 and hear a faint electric motor start running kinda slowly every time they turn the ignition on before cranking the starter motor that's what it is... the little 1" fan inside the auto heat sensor housing behind the ashtray starts running slowly as soon as the ignition comes on. Mine does anyway, so maybe the the wire for it is on the wrong fuse terminal up on the fuse box in the trunk.