Radio cuts out when AUX fan engages - PeachParts Mercedes-Benz Forum

locry · #1 07-13-2012, 09:27 PM

Is there something wrong with my AUX fan? I recently burned out a relay... had it replaced yesterday. It's working as it should... though now the Radio cuts out whenever the aux fan engages. It's like the aux fan sucks in voltage when it engages killing the radio. I attached a multimeter at the battery, voltage dropped around 1 volt momentarily when the fan engaged, I don't think this is enough of a dip to starve the radio of power. Am i testing it wrong? where should i attach a multimeter so monitor voltage INSIDE the car.

BTW, i think the reason the first relay burned out was because I was low on freon... so the AC was engaged the whole time, thus the aux fan was running 24/7 also... thus burning the relay. Correct assumption?

locry · #2 07-13-2012, 09:34 PM

Whoa!!! I was reading a thread about aux fans and came across a "resistor"... My fab is wired directly, full ON when the compressor engages. It's been rewired that way since temps here are always HOT. Pus it made things simpler... Anyway... could my fan not having a resistor be the cause of the current draw that's heating up my wires? If yes, whay resistor should I put in there? And where? What line? Thanks

I thought that the resistor just facilitated the hi and lo modes. Is it there to limit even the HI mode?

Aaaaand... how do I measure AMP draw? I have a multimeter, i just don't know where to connect it to test.

Gilly · #3 07-14-2012, 08:48 AM

An ammeter is put in line with the power, the power has to pass through the ammeter, so you could put the red on the fan side and the black on the power supply side. The fans draw a bit of power, as a minimum make sure your ammeter is good for 30 amps. Most would want to test it inductively, not an inline ammeter. I used an old "needle" type ammeter for work like this, I also used it for glow plugs on diesels.

I'd put it back to the way it's supposed to be, this sounds nuts.

The low fan stage is for AC and runs through a resistor to get the low speed.
High speed is for engine temp and is direct, no resistor, should have full battery current.

The theory of low freon causing the fan to run is faulty, at least on a properly wired car. Low freon pressure will cut out the compressor. It would also mean that the fan would never be on, as HIGH pressure makes the fan come on, not low pressure. The low pressure switch cuts out the compressor, the high speed switch turns on the fans. Unless you somehow have the 2 switches wired backwards???
Again I think it is not serving you well to modify the wiring just because you live in a hot climate, the car is designed for all climates, just leave it the way it should be, MB knows what they are doing.

ON the radio, I'd have to study schematics, but sounds like hopefully repairing (restoring) the fan system might fix it. If the cause is really what you are implying (which is possible) then I wonder if the battery is in good shape. As a test you could hook up jumper cables to another car and see if the radio then works with the fans on.
Gilly

locry · #4 07-14-2012, 09:54 AM

I failed to mention that the radio cuts out only momentarily and starts back up. I have to check if I still have that low pressure switch. The fans have been wired directly to the compressor clutch.

The thing is, the radio didn't used to do this. This is a recent occurrence, and what's funny is... we used the car just now, the radio was fine... as was everything else.
The fan being wired that way (faulty logic as it may seem) is to protect my #14 head...

well at least that's my excuse. hehe, if i had the funds and the time i would really like to refurbish all the wiring and switches back to stock.
The battery is new, replaced just last month. Old battery was spent, not caused by any issues with the charging system.
Thanks for the input!

Will get on with that ammeter test.

Gilly · #5 07-14-2012, 11:52 AM

Hopefully this shows what you need to see, you can just simply jump power to the fan through the ammeter if you want to do that. On digital ammeters there is usually 1 or 2 fuses in the meter which will blow if you try running too much current through the meter, so be sure to know your meters' rating and don't exceed it or you will need new fuses in the meter. Or if you have an old school needle type analog meter, usually they go up to the 50 amp range rating.

Quote:

Originally Posted by Gilly

locry · #6 07-14-2012, 11:54 AM

Ey thanks a lot!!!!! I appreciate it!

Yeah, I have the needle type multimeter. I wasn't really sure how to hook it up so that diagram pretty much explains it. Thanks again!

Gilly · #7 07-14-2012, 12:06 PM

If it is a multimeter, still be careful for the amount of load it will handle in the amp range, some multimeters won't even handle above 1 amp. The needle type I am referring to are dedicated for amps only and will handle a pretty good load.