So I pulled my 81 SC out of the garage for the first time in a month. Hey! This thing is fun in the cold dense air!
On my way to the office I pulled the two heat levers to warm up the cabin as it was 39F outside. After about 1/2 mile, I noticed burning smell as in melting plastic wiring. Very quickly there was smoke in the cabin. I pushed the heater levers back down and opened the windows to air out.

I have a non-automatic temperature heat control car. The red heat levers when raised flip a switch to turn on the heat ventilation motor in the engine compartment, is this correct? If not where is switch? When I got home this evening after meeting my “Lakewood Air Cooled Club” friends for a beer, I inspected the wiring at the motor and it appeared normal.

The Bentley wiring diagram is confusing to me. I’ve attached a photo. The heater vent relay has fused power in start or run mode, a red/black wire for the switch side of the relay, number 86. The Heater Ventilation Switch has power from a yellow wire during start? Shouldn’t number 85 of the relay be to a switch that connects to ground when closed?

If I melted a wire, I’m guessing it is the non-fused yellow wire to the switch, but I don’t understand why it is wired/designed/drawn this way.

thoughts? Charles in Dallas

 

Some thoughts based on my '85, which I don't know how similar it is to your '81:

Lifting the levers closes the limit switch, which turns on the heater blower back in the engine bay, and also turns on the left and right side helper motors in L+R footwell areas. So you can check down in those locations too for melted wires.

Also, (unfortunately) I know melted wires have a distinctive smell, but there's another possibility here, especially since it sounds like your heater system is used infrequently. As I recall, the motors (the front ones at least) have felt rings that are oiled kind of permanently to provide some lubrication. At almost 40 years, the oil may be gone and the friction may be smelling like cooking wires. So once you find those front kick panel blowers, if the wiring looks good, you can take a look at the blowers themselves to see if the smell is coming from them.

 

Can anyone confirm the SC has the forward helper motors as referenced by Oldskewel?
They aren’t in any diagrams or in the Bentley manual.

 

I pulled the rubber cover up exposing the mechanicals of the heater control levers between the seats. What I see makes sense. There are two yellow wires each connected to an independent mechanical switch which closes to ground earth when the lever is slightly raised. The idea is either passenger can independently turn on heat on their side. When the switch closes, the relay’s control switch circuit is complete to ground, thus the relay now powers the blower motor in the engine compartment.

So I turned on the ignition, pulled a lever and nothing happened with the blower motor in the engine compartment. My test light verified 12v at the blower motor so I’m guessing my blower motor burned up and it was its smell and smoke I had in the cabin. I’ll investigate further but probably purchase a new blower motor.

I took a picture of the levers and their switches but it is very hard to see what is happening in the photo. Each spring metal connector has a plastic insulator on the top tip to keep its contact with the lever isolated from ground. As you lift the lever, the spring metal falls back to touch a purpose grounding contact.

In the attached photo, the driver’s side lever is raised, and the spring metal switch is further toward rear of car making contact with ground, shown by green arrow which is partially covering black insulator. The red arrow is pointing to the passenger side metal spring and you can see it is further away and not touching the grounding plate which is the orange arrow.

 

Nope, no helper blowers in the front footwells of the SCs.

Mark

 

Thank you!


On another note, I’m going to reach out Bentley Publishing about their wiring diagram.

 

Probably your blower motor burned out. I had mine rebuilt once but find I get enough heat even without the blower. When it failed the second time I didn’t rebuild or replace. In motion the car still gets hot enough inside to burn my shoes.

 

yea these blower motors burn out a lot .. i went through three.. on my last one i decided to just gut it , put it back in for original appearance only the heat is plenty except it can fog up at a stop light as there is not enough air force to clear the windshield..

 

all the lever does at the em brake handle on an sc without automatic heat is ground the relay terminal to provide power to the blower motor. I would agree with the previous comment, the heater motor is burning out.

 

Yeah the bearings in my blower motor started failing a couple of years ago but seeing as how I lived in the south it didn't really bother me (now when the A/C started going, that was a different problem), and unless you're getting stuck in traffic on freezing days (why would you do this) you'll be okay.

Now, there are days in Alabama where it's 40F and 100% humidity, and there's nothing to be done for the fog except for wiping down the windshields.

 

I purchased a new heater ventilation motor from Pelican. Installation was easy, but bolting on the nut to hold the fan on, how is one to keep the motor shaft from turning to tighten nut?
On the old motor, to get the nut loose, I drilled a 1/4” hole in the but end of the motor case and stuck a rod inside the motor to stop if from turning.

I didn’t feel like jacking up the car to study the system, but when one pulls the heater levers, it opens the fresh air intakes over the axles, right?
The air is pulled through the exchangers and then pushed to the cabin by the ventilation fan? Where are the warm air tubes when traveling rear to front? And then it enters the fresh air system of duct work in the trunk?
So one can run heat by heat ventilation fan only and not have to turn on cool fresh air fan in trunk?
(SC model with factory a/c)