The danged A/C fuse started blowing, after about 5 minutes of run time.

New Compressor and blower motor about 5 years ago. The blower was a brand new Bosch. I did notice that the resistor pack is loose and trying to tighten it resulted in metal fatigue on the fender. It now has a secondary grounding wire connected to it.

What else can cause a large amp draw to blow the fuse besides the compressor and blower motor?

16 amp fuse on an A/C circuit is crazy low, IMHO.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Bump!!!

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

The blower motor draws about 16 amps as I recall when I measured it. I had bouts of blowing fuse 8 until I replaced it with a 25 amp unit in my 83 300D. You may want to try that after verifying the amps draw of the blower motor. Easiest way is remove fuse and replace with a properly rated ammeter. The compressor clutch draw is much smaller than the blower. Idk what it is. Please measure and report back.

The internal coils of the resistor pack should not be grounded.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Funola,

Thanks for the info. I'll check it and report back.

What I did on the resistor pack is ground the case, like it was before the screw holes wallowed out.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Mine used to blow that fuse, turned out to be crappy fuses, after I got some better ones the problem went away

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1982 300D Turbodiesel, daily driver. Mods so far: Fram 8038 paper filter, 4 brake light mod, Gen II w126 (front) rotors/calipers, boost turned up to 12lbs, non-egr manifolds, water/methanol injection, 4-speed manual
1980 300SD Turbodiesel, project car, nearly ready to hit the street

1974 240D, New paint

I posted earlier about my 1991 300d suddenly not blowing on the low setting. It will do it for about 60 seconds, then starts blowing on high. Someone mentioned the "resistor pack". What/where is that? We're not talking about the regular fuses in the fuse box, so what/where are they?

Thanks

Now that we know yours is a 91, the resistor pack may not apply to your car. Others in the know will chime in.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I don't think grounding the case matters. As long as the resistor coils inside the pack is not grounded to the case, that's all that matters. You can check that by unplugging the connector and measure from the pins to the case. You should not get any resistance readings from any pin to the case.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Funola, my crappy meter blows its fuse at 10 amps...go figure. Time for a new meter.

Anyway, with a bigger fuse, no issues. When I unplug the blower motor, the 16 amp fuse does not blow or even get hot. I have read that a Ford blower motor would fit, but they said an F series, The F150 blower motor number is different from the F250/350 motor. If the F150 motor fits, then cool!

Sorry for the long delay. Work and other car issues...

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

the problem may not be the fuse size but it's style.
MB realized that the clip in fuse holder is not capable of sustained amp draw from the blower...
so they moved the wires to an external fuse strip like the glow plugs use, and it solved the problem.
solution is not putting a larger fuse in, it's pulling out the fuse box, removing the wires from the #8 spot, and tying them to a larger better fuse block and putting in a good 16 amp fuse. or a strip fuse like MB did.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

A larger fuse has always worked for me and others. Last time I measured it the blower motor draw 16 amps on high. And the draw of the aux pump and mono valve and it exceeds what the16 amps fuse can carry.

Are you seriously recommending people modify the fuse box by rewiring it with an external fuse? It will work if done right but if not done right, can be a fire hazard. Why do extra work if just replacing the fuse with a bigger fuse will do? There is a 25 amp fuse in the fuse box already so it is the designed for 25 amps. No worries of the fuse box or wiring melting. Just use a ceramic body fuse, not the plastic ones.


Sent from my MB860 using Xparent BlueTapatalk 2

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

well... MB realized that the fuses fail when loaded this high... that's why they changed the design. if you are comfortable installing a 25amp fuse where a 16 should go, more power to you.
recommending on a website for MB maintenance that it's a good solution is like telling someone to put a penny under the fuse that has blown... it works right?

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

It is not like putting a penny in for a fuse. I already gave the reasons why I think it's safe.

Reiterating:

1. One of the other fuses is a 20 amp or 25 amp. So the fuse box is designed for more than 16 amps.

2. I have run a higher amp blower fuse safely in my 83 300D for more than 4 years.

After running the blower on high for an extended period, put your fingers on the fuse. If it's not hot to the touch. It's ok.

Is is possible Mercedes made a mistake putting in too small a fuse?



Sent from my MB860 using Xparent BlueTapatalk 2

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

What John said. At least for systems with transistor blower control, MB sells a external 30 amp strip fuse retrofit kit with all fittings for a safe upgrade. My uneducated opinion is MB didn't foresee the increased yet acceptable load as components age. FWIW, I haven't heard of the strip fuse retrofit causing problems but I've seen fuse boxes with melted ACC fuse holders. The retrofit is then the simplest solution forward.

Apologies to Pelican but this was the first google hit - http://www.ecklersmbzparts.com/mercedes-fuse-box-blower-repair-123-126-chassis.html

rrgrassi, the monovalve and auxiliary pump can fail such that the fuse blows. You might isolate these components in your search for the reason the fuse keeps blowing.

Sixto
87 300D

Do blower motors increase amps draw as they age? Someone with a new blower motor please measure its amps draw.

On W123's The monovalve and aux water pump does not blow the fuse. The former blows a CCU trace ( first hand experience), the latter can start a fire inside the CCU. It would be great if it blows the fuse instead but it doesn't, unfortunately.

Sent from my MB860 using Xparent BlueTapatalk 2

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked