Blower Fan Current Draw? - PeachParts Mercedes-Benz Forum

graycenphil · #1 05-04-2015, 02:10 PM

Does anyone know how much current the fan draws? Mine draws over 16 amps (my meter only goes to 16, and it pegs it), which seems high to me.

I only tested it because I am having a problem. The fan usually works when I first start the car, but quits after a few minutes. It will come back on again after a while, then will cut out again. If I rap on the panel next to the switch, it may come back on a for a bit, but I'm not sure this isn't just coincidental. This behavior happens at all fan speed settings, manual or auto.

So before I start taking apart the car to get to the climate control module, I wanted to make sure the fan isn't just drawing too much current and triping a circuit breaker. Does this sound possible?

Thanks.

Oh, it's an '84 300SD. Great car otherwise, 160K.

Maxbumpo · #2 05-04-2015, 03:19 PM

Sounds like you need to either replace the blower motor or replace the brushes in the blower motor.

No circuit breaker involved, just fuses. I think the current draw is about 25 amps? What size fuse provides power to the blower motor?

Jeremy5848 · #3 05-04-2015, 04:23 PM

I've never had an 'S' class car but the blower in your '84 300SD might be similar to the '82-85 300D, which has a 16 Amp fuse for its blower. I will say that 16 Amps is not excessive for a blower of that kind and many modern ones draw close to 30 Amps.

The blower could also be similar to the one in the 1986-95 E-class cars (model W124). This blower started out with a 25 Amp fuse but the factory retrofitted an external 30 Amp strip fuse (like the glow plug fuse in appearance) in 1987 after too many people reported problems with the fuse blowing or burning up the fuse box.

graycenphil · #4 05-04-2015, 05:31 PM

Thanks.

IIRC, it is a 30 amp fuse under the hood, but it may have other circuits on it as well. If it normally does draw 25 amps, I guess mine is working okay. If you "hotwire" it, it always works, so perhaps the problem lies in the climate control module.

SD Blue · #5 05-05-2015, 12:05 PM

I would suspect fuse F11 for possible bad connection or corrosion first. After that, I would suspect the blower motor itself. As mentioned, sometimes it just needs a new set of brushes. However, if the commutator is severely grooved, it makes more sense to just change it out.

The Pushbutton Control pretty much just sets whether you will manually control blower speed in Hi/Lo or allow Automatic mode controlled by the Blower Speed Controller.

Here are the schematics for the Automatic Climate Control:
http://www.startekinfo.com/StarTek/outside/12253/program/ETM/ACC83-85.pdf

graycenphil · #6 05-05-2015, 01:38 PM

Thanks, Sam. I will replace the fuse and clean the contacts, just to be sure.

I may hook up a test light to the fan circuit, so I can see if it is still getting current when it stops running

resto108 · #7 09-17-2017, 04:43 PM

I have an interesting problem. 83 SD. Fuse 11 gets so hot you can't touch it. It has discolored the power side of the fuse holder, but doesn't blow the fuse. 25 amp fuse. This fuse also runs the AC clutch, But I've disabled the AC for troubleshooting. Cleaned the fuseholder, changed fuse, checked the wires on each side of the fuse for cleanliness and tight screws. Seems to only get hot when fan is on high speed(s). I pulled the fan out and the brushes are worn. I put my meter on it and got 14 amps, but its only supposed to be a 10 amp meter. Also, the test connecter I'm holding on a battery while it runs gets hot like the fuse does. I'd replace the fan motor if I thought the new one would be different.

Diseasel300 · #8 09-17-2017, 04:57 PM

The wire you're using as a test lead should be rated to carry enough current. If you're using a dinky test lead, it's going to get very hot in use.

If you're pulling 14A on the fan motor, you should still be fine.

Fuses get hot because they have a poor connection with the fuse holder or the wires connected to the fuse holder are loose. Google "hot connection" for more graphic illustrations. Take some fine sandpaper and polish the sockets in the fuse holder until they're bright and shiny and try with a new fuse (brass or copper please). With 16a or so passing through it, the fuse WILL get warm.

The fusebox is marginal for the constant draw that the fan motor creates. Later models (1986.5 and later) went to an external fuse holder with a 30A fuse to put a stop to all the complaints of melted fuseboxes and nuisance blows of the blower fuse.