Ok, so when I pull up the red floor levers I get some air at my feet.
But, if I turn the dial to "3", I should be able to hear a 2nd fan/blower down right at my feet, right?

For reference, the part number for these footwell blowers is
Left-91162404302
Right-91162404402

First, I verified the 3 fuses in the engine compartment wing nut panel were intact.

I then removed the driver's carpet kick panel,
and saw the footwell blower's inline 15A fuse was blown.

I replaced it with a 10A fuse.
Ignition key in position 2.
Heat lever pulled up (Engine blower now running)
I turned the dial to 3, and the 10A fuse blew instantly, with a spark!
Blower motor never spun.
Ok, that might explain the 15A fuse?

I then put in a 15A fuse, and again tried "3" on the dial.
Nothing. Motor still dead.
Fuse got real hot within a few seconds. I turned the dial off.
I thought I could see a wisp of smoke.

Do you think the blower motor is stuck frozen?
Would that cause the behavior observed?
What is the next step in diagnosing this?

Is it easy to remove the footwell blower and try to get it unstuck?
Would the dead footwell blower also explain why I am not really getting heat in the windshield or the side vents?

You should get some heat through the upper dash vents, no matter what. Your engine cooling fan is the primary source of airflow. Some of the air for cooling the motor is bled off into ducts that supply the heat exchangers with air. The additional blower in the engine compartment and the footwell blowers are there to add airflow at low engine speeds. You can heat a 911 without having either of them.

Your footwell blowers are toast. You might remove them and try to resurrect them, as they are expensive to replace. Do a search for the info on how. Don't ever use a larger fuse than what is suggested, the last thing you want to do is fry the wiring and other parts of the system.

Take another look at the upper dash vent heat output while driving (not the face level vents, or the ones at the side, just the ones at the base of the windshield). Keep the engine around 3,000 rpm, and make sure the fresh air side of things is shut off completely. Is there NO heat output there, or just a WEAK output?

JR

Thanks for your help on this one, Java.
I now have a much better understanding of the heater system.

In my case, the blower motor was just stuck.
I was able to remove it and break it free.

Now, it's obvious to me how to know your footwell blowers are dead.
You'd hear them spinning down near your feet very clearly once you turned the round dial.
I think the footwell blower sends air up to the windshield vents and the side vents, which would explain why it was so weak.

The booster fans just add output. Plenty of 911s get along just fine without them. Your car should have far more than "zero" output without them running.


JR

Yea, without the footwell blowers, air was coming out, just not with much force.
It was usable, but I am enjoying troubleshooting the footwells.
Wow, when they work, it's a massive difference.

Tonight, I removed my passenger side blower ...It was also dead.
Compared to the driver's side, the passenger motor squirrel cage was harder to spin.
So, I tried to lube the squirrel cage, and it spun a little more freely.
I never opened the motor. Just lubed the plastic contact points.
Now, the passenger footwell blower motor works....but inconsistently.

I used my multimeter to test the voltage at 0,1,2,3.
I verified the passenger motor is getting low voltage even at 0/1, but not spinning. It spins only on 2 or 3.
This must be that hack they introduced to automatically have the fan spinning when heat was on.
So, the motor is not fully working as it should.

Is it worth trying to open the motor and clean and lube it?
Anyone know how this is done?

So here's a topical related question - are there any shared circuits for the footwell and engine compartment blowers on an '84? In other words, is there any single point of failure that could kill all three blowers?

Here's the deal - I know for a fact that the engine compartment blower and at least one of the footwell blowers was working when I drove the car last week. All 3 speeds worked for the footwell blowers, and I heard the engine compartment blower running when I turned on the ignition (engine still off). Tonight on my way home from work, no blowers at all. Hard to keep the windshield defogged in stop and go traffic.

I've checked the obvious fuses, all seem fine. Haven't had time for systematic troubleshooting yet.

Worse, the wiring diagram in my Bentley doesn't seem to be accurate, seems to assume that all '84s have climate control. (Not true in my car for sure, maybe wasn't even offered in '84?)

Any hints on a common failure point to check? If not, this weekend I'll have to start by jumpering the blowers themselves (make sure they aren't seized) and working backwards from there.

If the engine compartment cabin heat blower does not run then the footwell blowers are disabled. The cabin heat blower control module "monitors" the electrical current flow of the cabin heat blower motor and if it isn't above a certain level the footwell blower power circuit is opened.

Direct wire the cabin heat blower to see if it works.

Perfect. That's the piece I was missing, it makes sense. I couldn't believe that all 3 blowers "just happened" to die at the same time. I'll start at the engine compartment unit.

I have seen reports that seem to indicate that at idle and with a low battery the engine blower does not "draw" enough current flow to close the footwell blower circuit, raise the RPM a bit, footwell blowers run.

Once the DIY solutions I have seem is to bypass the "monitor" reed relay in the cabin heater control module...

NOT a good idea since that might/would result in the footwell blowers drawing in exhaust fumes from under the car.

I'm please enough with how the system worked before the failure. I see no reason to modify or backdate it - I just want it to work.

So, what's the next step?
Applying direct current to the engine blower motor?

This thread has links to the enture $350 assembly and just the $175 internal motor assembly. (ouch)
http://forums.pelicanparts.com/porsche-911-technical-forum/727692-engine-compartment-heater-blower-motor-88-3-2-a.html

This thread talks about the heater blower relay
http://forums.pelicanparts.com/porsche-911-technical-forum/236844-heater-blower-relay-84-carrera.html

Yes, indeed. Might get to that tonight, but maybe not until Saturday.

But wait...there's more...

Here you go...more information about the heater system than anyone should have to wade through. If you have nothing better to do this weekend most all of your questions are answered in these posts. Even some you haven't asked yet. Be aware that some discussions were a journey of discovery, so read carefully and completely to get the entire picture:)

http://forums.pelicanparts.com/porsche-911-technical-forum/388445-carrera-removing-engine-compartment-heater-blower.html

http://forums.pelicanparts.com/porsche-911-technical-forum/97297-carrera-replacement-heater-blower-long.html

http://forums.pelicanparts.com/porsche-911-technical-forum/258473-help-does-anyone-understand-footwell-blower-circuit.html

Good luck...

Checked power to engine compartment blower, 12v. Good.

Pulled blower from car, disassembled. Brushes are totally worn out. One wore far enough that the copper braid lead came loose. Motor dead.

Might be worth looking for replacement brushes that would fit, but don't know how easy those are to find these days. Would be far more affordable than a replacement motor. But if it takes a new motor to fix it, so be it.

Thanks to all for the info and support on this.

Maybe worth a look....

Factory Air Blower Motor Wheel - 35214 - Page:2 - Detroit Motor Parts

Find OEM Specialty Blowers and other Fans & HVAC Equipment at Zoro

Blowers / Jabsco Blowers / Fans & Blowers / Marine Products / Xylem JabscoShop - Jabsco & Rule Pumps and more - from the experts

Your local electric motor re builder should be able to get brushes for you for $20 or less.

Sometimes you can find something close that is a little bigger and whittle them down.

Get a can of electrical contact cleaner and clean everything. 1000 grit paper
For armature and a dab of lithium grease for bushings if they are just dry and not
Worn out.

Keep us posted.

Did a little digging, and decided that in addition to the brushes being shot, the bearings are questionable at best. And while they too could be replaced, when you add those bits to the desire to have a working defroster system sooner than later (cool and damp now here in Western Oregon, and I drive the car regularly, even in the rain), I went ahead and ordered a new motor (the aftermarket replacement) from our host. I'll keep the original for possible parts use later.

Will also be looking at the footwell and ventilation blower motors later, as I suspect they may not be much better inside. Time for a little preventative maintenance.

The link in the OP may be helpful in the footwell blower area.
Good chance they are just stuck with a blown fuse.

Dumb question, after reading the posts. It isn't clear, are the footwell blowers just for heat or fresh air as well?

EDIT: Went and checked them out. Appears they only come on with the heater, no AC or fresh air. And my passenger footwell blower isn't working. Eh, it will be on the bottom of the list to do. It is Texas and I hardly ever have a passenger in the car. :)