smoke comming from heater fan

[freebaum]

Whenever I turn on the fan for my heater after awile i start smelling a burning. How do I trouble shoot and repair.

[fazool]

Which model and year car do you have ?

The heat source itself won't create that smell, so its likely coming from your blower (fan) system. Either your wiring or the switch but most likely either your blower motor is on its way out or your resistor module is failing. Try running the fan without worrying about temperature (in fact set it at cold if you want but run the fan and see if it smells. Try this at each fan speed. It might smell at one or two speeds, suggesting a bada resistor module

[freebaum]

Its a 96 850. And it makes a screaming sound too.

[BEJinFbk]

It sounds like the motor has bad bearings.
The more friction that they create, the more current the motor draws.
The magic part that tells the motor how fast it should be going is getting too hot.
That part is designed to get hot, so it's mounted in the duct next to the blower.
When the blower is running and the speed controller gets hot, the fan keeps it cool.
Since your motor is asking more of the controller than it's meant to give, it overheats
and being in the duct, comes out the vents and that's what you smell. The motor
itself is mounted in the dash behind the glovebox and is outside the duct system.

So - Getting a little more specific, there are two versions
of climate control systems that came in your '96 850:

MCC - Manual Climate Control

850 MCC panel.jpg (110.62 KiB) Viewed 1321 times

This system uses a resistor pack to control fan speed. But when you run the fan at speed 4,
it bypasses that set of resistors. The smell may go away at speed 4, but you still have a bad motor.

and

ECC - Electronic Climate Control.

850 ECC panel.jpg (146.21 KiB) Viewed 1321 times

The ECC uses a transistored speed control for fully variable speed.
It's in the same location, just the the left of the motor in the duct.
But these usually die if you smell anything hot...They generally fail
with the motor stuck on full blast or just plain no motor at all.
And that still tells you - Bad Motor.

What you need to do is either pull that motor, take it apart and lube the bearings
or just put a new one in. And do it soon, because no matter whIch speed controller
you have, it's not going to last forever overheating and trying to run a bad motor.

[fazool]

Excellent writeup BEJinFbk