A/C Fuse keeps blowing - Page 2 - PeachParts Mercedes-Benz Forum

sixto · #16 08-22-2013, 12:45 PM

Did the compressor come with a new clutch? I had a misaligned bearing wear a short circuit in the clutch coils which blew the fuse when the compressor engaged.

Sixto
87 300D

sixto · #17 08-22-2013, 12:53 PM

Quote:

Originally Posted by funola

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

They can. The blower can get more difficult to turn as the bearings wear requiring more current to start and possibly to stay running. I'm no sparky but I think if you hold the blower cage then set the blower to MAX the fuse will get hot and eventually blow. That's it's job unless the blower windings dissipate the heat or themselves blow.

Sixto
87 300D

funola · #18 08-22-2013, 12:53 PM

Rgrassi, I keep forgetting you do not have a W123 so everything I said may not apply to your car.

The fuse box in the W123 looks like it is made from Bakelite, which has a melting point much higher than most plastics.

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sixto · #19 08-22-2013, 12:55 PM

Looks like a 123 in his sig line.

Sixto
87 300D

sixto · #20 08-22-2013, 01:00 PM

Here's some discussion of a 123 melting ACC - or just CC since the OP is asking about a 240D - fuse holders - melting fuse box but not fuse

Sixto
87 300D

funola · #21 08-22-2013, 01:02 PM

Quote:

Originally Posted by sixto

They can. The blower can get more difficult to turn as the bearings wear requiring more current to start and possibly to stay running. I'm no sparky but I think if you hold the blower cage then set the blower to MAX the fuse will get hot and eventually blow. That's it's job unless the blower windings dissipate the heat or themselves blow.

Sixto
87 300D

By aging motor I meant a healthy running unit, not one jammed shut or filled with debris. My 83 w 297k with what I believe the original blower ran and sounded fine and draw 16 amps on high.

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sixto · #22 08-22-2013, 01:09 PM

I meant age as a surrogate term for accumulated wear. I suppose time installed and time in service don't necessarily cause wear. If all that wears is the brushes, you should be good until they wear out. That shouldn't blow the fuse.

Sixto
87 300D

rrgrassi · #23 08-22-2013, 02:47 PM

I do have a W123. Fuse 8 does get hot and it has melted the plastic. I do have a 1 amp fuse on the aux water pump. I did that 5 years ago, and it still has not blown. Never thought about the monovalve. I have replaced the diaphragm about two years ago though.

Any recommendations for a multimeter that will handle 20 to 30 amps?

All my GM older cars used a 30 amp fuse for the HVAC system.

I know the MB is drawing more that 16 amps and less than 25, since the 25 amp fuse has not blown.

funola · #24 08-22-2013, 03:04 PM

Quote:

Originally Posted by rrgrassi

I do have a W123. Fuse 8 does get hot and it has melted the plastic. I do have a 1 amp fuse on the aux water pump. I did that 5 years ago, and it still has not blown. Never thought about the monovalve. I have replaced the diaphragm about two years ago though.

Any recommendations for a multimeter that will handle 20 to 30 amps?

All my GM older cars used a 30 amp fuse for the HVAC system.

I know the MB is drawing more that 16 amps and less than 25, since the 25 amp fuse has not blown.

HF has a meter with a 20 amps input, it also has a thermocouple input which is very useful.

The monovalve blows the CCU trace only if you short it. I did that twice and fixed it twice, about 4 years apart on my 83 and 85. Both times while taking the connector apart to tighten the contacts, forgetting power was on. This reminds me to add fuses for the aux pump and monovalve in my 85 so the CCU will never blow again.

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sixto · #25 08-22-2013, 03:35 PM

I use an aftermarket ammeter like - http://www.summitracing.com/parts/sun-cp8204 - to measure higher current draws like blowers, fans and glow plugs. Not very accurate but a reading within 20% tells me what I need to know. HF used to sell one for like $5 but I don't see it in their website today.

Sixto
87 300D

MBeige · #26 08-22-2013, 03:57 PM

When I got my '83 300D there was a 25A fuse in the #8 slot. There was a time when the fuse kept blowing too. Replaced the blower motor brushes and this has solved the problem (perhaps apart from a new set of fuses also).