I have a faint-to-moderate electrical burning smell coming from the air handling system on my daughter's car. This car has automatic climate control (though the AC system has been fully discharged for probably the four years). She isn't a smoker so it isn't cigarettes. In the past with older American cars, this same symptom has been dust/dirt burning off on the blower resistors (used to changed fan speeds). The automatic temperature control seems to change speeds normally and it is of course gradual (acts like a potentiometer is used instead of a bank of resistors) so I don't think the problem is necessarily this simple but I'd like to know if this car has such resistors and where they're located. I see in my manual there are resistors for the aux fans but no mention of blower speed resistors. One more note, I noticed this smell roughly two months ago so the car is drivable but unpleasant to sit in. Last week , my daughter skidded on some ice and went over the curb backwards. No damage to the body . Had Goodyear check out the undercarriage, steering, suspension, brake lines ,etc. and put on two new tires. I bring it up because the blower's 30 amp fuse blew. I have it currently hot wired and am purchasing a proper fuse. Could the jumping the curb cause the fuse to blow or is this indicative that the blower motor is probably dying?

No resistors. If the fuse is blowing the blower is drawing too much current. See what it's drawing, lube the bearings with just a little ATF, check current draw again. OR, since its already apart at this point, put in a new one and be done with it.

__________________
Hanno
'79 6.9 Sold (after 27 years)
'83 280SL, 5 spd.
'94 E320 Sdn. 5 spd conversion
'02 E320 Sdn.(on loan to mom!)
'87 300E (5 spd. conversion) Sold
'05 E500 Wagon

I don't have it apart yet. How do I measure the current draw?

No need to take anything apart except an electrical connector to check what you have going on now. three wires run from the bulkhead near the master cylinder to the blower. +12, ground, and control voltage. Search this site, its all there. Checks both the motor and the speed regulator, and output of the CCU.

__________________
Hanno
'79 6.9 Sold (after 27 years)
'83 280SL, 5 spd.
'94 E320 Sdn. 5 spd conversion
'02 E320 Sdn.(on loan to mom!)
'87 300E (5 spd. conversion) Sold
'05 E500 Wagon

Be careful about hot wiring something that blew a 30 amp fuse. If there is a hard short, you could do lot of damage toyour electrical system.

Since you ask about how to measure the current, I assume you don't own a clamp-on ammeter or a shunt resistor. A new 25 and 30 amp fuse makes for a crudely effective ammeter.

Like the older MBs with the resistors, the fan controller is located at the fan, above the passenger side floor board. Like the resistors, the integrated circuit fan controller reduces the voltage by turning it into heat. There could be some insulation or other material that has dropped down onto the controller, causing the burning smell. A loose connection at the fan or bad fan bearings could also increase the current, causing the wire insulation to burn. Does it smell like burning paper or burning rubber?

Either way, you need to remove the cover above the front passenger floor board to have a look.

Thanks to both of you (hanno and knuckle-buster) for the advice.
I agree, hot wiring this was a bad idea so the sooner I get a real fuse back in there the better. I am going to the local pick-n-pull tomorrow and I should easily find several fuses (there are some recently added cash-for-clunkers parked there).
The smell is not burning-paper, definitely more electrical/rubber.

I do not own an ammeter so I like the idea of inserting fuses. I'll start with 25 amps and keep going up until I see which value will hold the blower on without popping. I suspect that anything fuse over the 30 amp "design" value is reason enough to fix something. I'll look at the fan controller you mention. My daughter has taken the car for the next few days so I won't get a crack at the problem until mid-week.

FYI....I haven't had the smell for a while now and everything seems to be working ok. It could have been something else burning in there for me that I will learn about later when I need it! The only thing that happened a little while later that was was strange is that my upper radiator hose cracked and sprayed all over the engine but I was thinking before it did that was it being sprayed back by the fan and burning on the engine working its way through my vents? I'll keep you posted.