Question for '86 911 Turbo owners: footwell fan operation

[logician]

This question is specific to the '86 Turbo, which has a different heating controller than the 911. With the heat control dial (knob between the seats) on my Turbo turned to zero, the footwell fans are on, but at their lowest speed setting. After tracing out the wiring in the controller, and looking at the schematics, I'm starting to be convinced that this is the normal operation for an '86 -- seems strange.

If you have an '86 911 Turbo, can you check if yours is the same, and report back? Actually, you may not notice at first, as the fans are relatively quiet at their lowest setting. It helps if the engine is off, but the ignition is on. Don't confuse the footwell fan sound with that of the temperature sensor, which is in the dashboard to the right of the steering wheel.

Thanks in advance for any help!

-Juan

[javadog]

Juan,

Mine are not on with the control knob set to 0.

JR

[Mysterytrain]

This is normal. It seems that around 85/86 [correct me if I'm wrong] the factory began to see problems with the old design. The first problem was that the footwell blowers were not fused. So a change was made and inline fuses where added to each blower to protect you from the second problem. The second problem was that the heated air cooked the bearings. The more began to draw a lot of current becasuse it wasn't turn and the wiring began to burn! The spinning blower helped to keep the air moving and extend the life of the blower and perhaps the car. So, the factory just changed the wiring a bit so that anytime you called for heat..the blowers would spin.

[Emission]

I've never noticed, and always thought mine were "off" when set to "0" (at least that is what I believed).

Let me go out and check...

[Emission]

OK, now you've opened a can of worms!

With the key to "ignition" and the control to "0" I hear nothing but the noise of a fan (or something) near the ashtray (on the dash). Mind you, my dash blower is "off" at this point.

If I move the control to "1" or "2" or even "8" I hear the servo in the control unit spinning away for a moment, but I still don't hear a fan blower... is mine burnt out?

Does it wait for the car to be warm? I don't think it is that smart...

Now, if my car is on the highway, and I turn on the heat, I do get warmth. Maybe it is all forced?

[logician]

Emission,

The small fan you hear by the ash tray is in the temperature sensor. You can ignore that sound.

My follow up question for you (and also javadog) is: does your footwell fan ever come on? Try warming up the car and try at 8, 9, and defrost settings. If the fan does come on, then does it turn off when you set at 0? At the higher settings, the fans should be loud enough to hear even with the engine running. The fans are located in the driver and passenger footwell, behind the carpet.

If the fan never turns on, then you have another problem, likely a blown fuse, and you won't be able to answer my question.

Thanks,
-Juan

[Emission]

Juan,

I would assume that the heater isn't intelligent enough to wait for the car to be warm. In 1986, that would have been pretty advanced - most all cars would just blow cold air until the engine (or coolant) was warmed.

Let me try mine again at the highest setting (defrost, I think) and see if anything happens. I will be trying it with a cold car, as my garage queen only goes out on weekends!

If it is the fuse, is it underhood or somewhere else?

- Mike

[logician]

Mike,

Thanks for checking it out. The system does have a temperature sensor at the flapper that I think is designed to keep from blowing cold air. So you might need to warm the car up to get the heating system to work completely. I belive there is a fuse in the trunk fuse box. Ron also pointed out that there may be an inline fuse as well, but that doesn't show up in my schematics.

-Juan

[logician]

Ron,

Do you think the fix from the factory was to leave the blowers running even with the heat off? That's what I am seeing.

Also, I see that there is a microswitch that turns off the blowers when the flapper valve opens all the way -- full heat. Do you know if that is part of the same fix?

-Juan

[DougM]

On my '86, the knob between the seats simply controls the amount of cool air that enters the system from the heater flapper boxes. The output correlates with the rpm of the car(fan blowing faster). The knob simply controls the degree of heat and not the output.

[logician]

Doug,

Your footwell blowers are not working. Check the fuse in the trunk.

-Juan

[Emission]

Which fuse is it? All 21 up front look good, and the big three exposed in the back look good too...

[logician]

Emission,

The locations of the fuses are indicated on the fuse-box cover. Looking at my cover, and counting from the rearmost fuse toward the front, it looks like it is either the fifth or eighth fuse. You might as well look at them all and investigate any that are blown.

-Juan

[Emission]

Yeah, it looks like you count from 1-21 starting from the rear (windshield). Mine all look good.

In the back, I removed the fuse cover and found the three fuses and relays. They all look good too.

Tomorrow I will drive her and heat her up and check the fans. This is now driving me nuts. I should never have read this thread. :-)

[Mysterytrain]

I'm not sure if the inline fuse ever made it to the schematics. Yes, there is a sensor on the heat flapper and I think its function is to not allow the blowers to operate until the heated air reaches a set point. Most of my experience is with the manual systems. Those systems have a micro switch under the levers that trigger the relay in the engine compartment or in the case of the carrera's the engine compartment controller and allow the blowers to operate. There is a wealth of info on the system in these threads.
Help! Does anyone understand the footwell blower circuit?

Footwell blower thread closed?

[javadog]

Juan,

My car runs the fans at low speed when the dial is in positions 1-7. Select 8 or 9 and the fans run in the 2nd speed. Select defrost and the fans run at high speed. Coincidently, this is what the owner's manual describes. In all temperature ranges, there is a delay between selecting the temperature desired and the initial onset of fan operation. This is not dependent upon temperature. The system simply waits until the servo motor has finished moving the cables to the point required by the temperature setting and then it turns the fans on to whatever speed is appropriate for the selected temperature. The fans don't always run if the temperature in the cabin is high enough. In other words, if the system senses that it can maintain the desired temperature without running the booster fans, it does not run them. This is also mentioned in the owner's manual.

Hope this helps you,
JR

[javadog]

The 10A in-line fuses were added to cars produced from April 23, 1986. The serial numbers for cars with fuses start with:

...910GS121913
...911GS161516
...916GS171278
...931GS051081

The fuses are located about three inches ahead of the electrical connectors for the blower motors. The part number for the fuse is N 017 1315. This info is from a TSB from July 9, 1986.

JR

[javadog]

Emission,

If your fuses check out and your fans are the original ones, they are probably toast. Some people have had luck repairing them but I've never tried to do so. I just write another check for a new one, or two.

Since you live in a warm climate and use the car as a weekend toy, I'd suggest removing them if they are bad.

JR

[Emission]

Originally posted by javadog
Emission,

If your fuses check out and your fans are the original ones, they are probably toast. Some people have had luck repairing them but I've never tried to do so. I just write another check for a new one, or two.

Since you live in a warm climate and use the car as a weekend toy, I'd suggest removing them if they are bad.

JR

I'm going to warm the car today and check the fans. I don't think I've used the heater but maybe three times in the past four years... I can live without it (I'd rather throw the money towards A/C).

[Mysterytrain]

Javadog,
What year/model car do you have? I'm trying to gather up information so I can posted it and add to it as we find out more about these circuits.