WARNING: Aux fan failure can cause fire. Preventative fix inside. - PeachParts Mercedes-Benz Forum

300SD81 · #1 05-18-2015, 02:03 PM

Actually, upon further inspection of the circuit, there seems to have been a major reversion in 1991. For the 1991 model year, the aux fan circuit contains NO FUSE. WTF MB?

The above fix works if you have anything other than a 91. If you have a 91, do the above and then cut the red wire going to the high speed relay, and insert a fuse holder inline. I guess 15 or 20A would be about right.

1990 and older. Fan circuit is protected by fuse.

1991. No fuse in circuit, add one.

tyl604 · #2 05-18-2015, 04:33 PM

I have a more basic question. Which fitting to you use to add Freon? And do you hold the can upright or upside down? How do you identify the correct fitting?

Hit Man X · #3 05-18-2015, 10:11 PM

Quote:

Originally Posted by tyl604

I have a more basic question. Which fitting to you use to add Freon? And do you hold the can upright or upside down? How do you identify the correct fitting?

If you are asking questions like this, you really need to learn more about auto HVAC before jumping into it as you can very easily kill the compressor and injure yourself big time. At the very least, read everything on the MB CDs for the W126 and take the EPA test so you can buy R12 legally, you will learn quite a bit.

How do you know your compressor is good? If low, does the system hold vacuum... if so, how are you certain? Where did the previous refrigerant go? Are you planning to just add refrigerant and not check head pressures? How do you know what refrigerant is still in the system? Did you know 134A and R12 use different oils and are not compatible?

In any event, I agree the resistor is in a poor location. I vacuum out in there often. I like having the ability to use 'auto' and low speed so I keep that area clean!

Just finished a rewire of that area in my 300SD due to a small fire, all the HVAC did was high speed. Pretty annoying. The repair was a big time PITA... booster has to come out to really get in there.

300SD81 · #4 05-18-2015, 11:44 PM

Quote:

Originally Posted by Hit Man X

In any event, I agree the resistor is in a poor location. I vacuum out in there often. I like having the ability to use 'auto' and low speed so I keep that area clean!

Just finished a rewire of that area in my 300SD due to a small fire, all the HVAC did was high speed. Pretty annoying. The repair was a big time PITA... booster has to come out to really get in there.

This isn't the blower motor resistor, but the resistor for the electric fan infront of the radiator. I definitely wouldn't want to eliminate low speed on the blower. Is there another one there on the 300? My SD is parked at my mom's house until I finish an engine rebuild, probably in like 5 years at this rate. The 560 only has 1 resistor there.

I'm tempted to slap together a circuit to get rid of these resistors and use PWM. Less wasted power, no heat, and software-adjustable fan speeds.

Carson357 · #5 06-02-2015, 03:15 PM

Quote:

Originally Posted by 300SD81

Actually, upon further inspection of the circuit, there seems to have been a major reversion in 1991. For the 1991 model year, the aux fan circuit contains NO FUSE. WTF MB?

The above fix works if you have anything other than a 91. If you have a 91, do the above and then cut the red wire going to the high speed relay, and insert a fuse holder inline. I guess 15 or 20A would be about right.

1990 and older. Fan circuit is protected by fuse.

1991. No fuse in circuit, add one.

instead of adding the fuse holder i opted for a relay that had a fuse built in.
001-542-96-19 this relay is identical to original minus the color and fuse