No Heat and It's getting COLD

[RNajarian]

Fall is here, Winter is coming and my '75 S has no heat at all.

After 3.0 engine transplant car has no heat. I need to check flapper boxes but my question is regarding the blower motor in the engine compartment.

The blue 25 Amp blower motor fuse in the engine compartment blows when the engine is on, regardless of the position of the fan speed lever. When I pull the electrical connection to the rear blower motor the fuse does not blow. When I check current at fan connection I get 12.8 volts.

Obviously problem with blower motor HOWEVER the electrical connection at the blower reads 12.8 volts regardless of where fan selector lever is ( 0 - I - II - III)

Any thoughts why electricity at the blower motor is constant 12.8?

[fintstone]

That fan only runs at one speed. The only fan selector lever on a '75 is for fresh air coming in from the front of the car. Maybe this will help:
911 Auto Heat

[scotricker]

The fan speed lever on the dash is for fresh air intake from the front vent below the windshield. It has nothing to do with heat.

The bottom red lever on the dash however, does control the path of heated air up to defrost, or down to footwell, after the heat levers on the floor have been raised.

The heat levers on the floor next to the e-brake have two functions. One is to open and close the flapper valves, and also to activate electrical switches that turn the rear blower motor on and off.

I just got done going through all this recently...

Check electrical current and connections at the switches on those levers. Pull up the boot and give it a look.

I think your car probably will be the same, that's what I looked at on my 78.

[RNajarian]

Thanks Guys. I've got a good starting place with your help. Hopefully I can work it out . . .

[RNajarian]

Poking around the front blower area I found this stray wire coming out of the firewall into the front trunk area. It is in the general vicinity of the front blower also near the Logic Relay for the seat belt system.

Any thoughts what this wire is for? Could it be related to the front blower?

The wire sits on top of the orange handled screwdriver.

Thanks Gang

[ossiblue]

IIRC, all wiring to the front blower is through the plug to the blower housing. I don't recognize that wire but someone will surely know what it is.

As stated before, the blower in the engine compartment (which blows the fuse) is designed to run all the time--as soon as the ignition is turned on in a 75. Since you have power to the lead, it sounds like the fan itself may be the problem. Can you get the fan to run when you apply direct voltage? Possibly the bearings are bad and the fan is frozen, or there is a short to ground internally.

[RNajarian]

Ahhh Fantastic!!

I'll take the blower motor apart and make sure all is well inside!!

Makes Sense. The fuse would blow whether the defrost/heater levers by the seats were UP or DOWN, and the Front blower lever on 0 - I - II - III

This helps A Lot! Thanks

[James Brown]

Don't confuse the engine blower for the fresh air blower in the front trunk. two different things, concentrate on the rear blower. The heat levers when up, supply warm air through the flappers to the inside of the cabin via ducts to the windshield or the footwells. the blower in the engine assists the air on it's journey. If you slide the top (fan) controller to the right, the blower motor in the front trunk will start to blow fresh, cold air to what ever the lower controls are set at. (and if the car has AC, a third blower will push cold air out the center vents but don't worry about that).
So, if the engine blower is not working and the flappers are closed (levers up) not much heat will come out, if any. Check that power is going to the blower then see if the blower is working. Several threads on here about finding a replacement blower motor as these can be pricey.
You can also remove all that engine blower stuff and go with a back-date heater system in the '75. I did this on my '81 and now I have more heat than before. so much for progress

[tcar]

Originally Posted by RNajarian

the Front blower lever on 0 - I - II - III

That has zero to do with the heater.

Additionally, try applying 12V directly to the REAR blower before taking it apart to see if it's able to run at all. Do a search to see ways to repair/replace the motor... lots of info here.

[Halm]

Originally Posted by tcar

That has zero to do with the heater.

Do I have this right. . . Heat into the car is at a constant speed equal to that of the engine compartment fan?

If so, would this be true for my '80 SC as well?

Thanks.

[James Brown]

yes the blower lever on the dash has nothing to do with heat!

[RNajarian]

UPDATE

Thanks A Million you guys!! I've got Heat!! The rear blower motor was blowing the 25 amp fuse so I hooked up another 12 V motor which worked fine.

So I took the rear blower motor out, swaped out the copper coiled steel rod from inside the motor with a clean one from my 1975 S motor, put it all back together and the blower worked!

I verified the flapper boxes worked and VOILA!! HEAT.

I may take my extra blower motor (and housing) from my 1975 S motor and try and rebuild that to get even more airflow, but that's a project for another day.

Thanks again for all your help gang!

[James Brown]

OK, now for our bill......we want some pictures and a write-up on how you fixed it so future Pelicans can do it to there cars. Kind of like "paying forward" and you can look like a hero! (BTW thoese future 911 owners are still in highschool).

[RNajarian]

My pleasure my friend. I'll get some photos and post it here.

Again THANKS!! Now that there is heat my wife will be happy, and everyone knows if SHE ain't happy, then HE ain't happy.

[LeakProof]

I took apart my rear blower motor twice and fixed it. worked for a while each time, then failed on the coldest days.
This time I'm ordering new.

Leakproof.

[RNajarian]

Disclaimer: I'm just a Pelicanite, not a mechanic, just a weekend wrencher

As you can see in this thread, I started out with no heat after a 2.7 to 3.0 engine upgrade.

Here is my testing . . .
When I pulled the heater levers up -no heat
When I turned on front blower motor with heat slide to right -no heat
After inspection of rear fuse box -blue 25A fuse blown
Volt meter put on rear blower motor electrical connection -0 Volts (motor running)
Visual Inspection of flapper boxes -seem to open/close ok

1) First I replaced the blue fuse, which IMMEDIATELY blew when engine was started.

2) Next I replaced the fuse again, but removed the electrical connection to the rear blower motor. With engine started the fuse DID NOT blow.

3) I verified 12.8 volts at this connection with motor running, and verified current with a known good 12 motor.

DIAGNOSIS BAD BLOWER MOTOR
I took apart the 3.0 blower motor and found it to be the problem The armature (the copper coiled steel rod) had some corrosion which was obviously the source of the short.) Since I had the blower motor from the original 2.7 engine, I was able to rebuild the 3.0 blower motor using the good armature from the 2.7 blower motor. Once everything was put back together I bench tested the motor and it worked well, the squirrel cage rotated freely and produced a lot of air flow.

I replaced the blower assembly in the car and once hooked up it ran as designed with the engine started. According to Pelican "Ossiblue" in my 1975 S this fan runs whenever the motor is running. This replacement blower motor is available from our host, part number 911-624-151-03-M78 for $459. (photo below)

I started the motor, and in a short time heat was coming from my defrost vents. The writing on the climate control unit tells you how to get the most heat for defrosting the window. Move the RED lever to the right, and make sure the top two levers are on the left.

The heater unit is DIFFERENT than the front blower unit. They work independently. The heat levers as you know are the red handled levers in between the driver and passenger seats. Below are a few photos of the areas I wrote about.



Rear Blower Motor


Pelican Parts Blower Motor (911 SC 1978-1983)


Rear Fuse Block



Dash Climate Control Unit

I hope this helps anyone in a similar position. Thanks to all those who guided me to my successful result.

[James Brown]

Nice job, way to go, good write up. now, lets tear that 915 out and rebuld it!!

[fintstone]

Good summary and photos!