The other day, my ’87 300E starting blowing fuse #7 when I turn the A/C on. Everything on the car works great until I engage the A/C and then the fuse pops. I scoured the A/C threads here and ran some diagnostics based on what I read (thank you Brian C). Here’s where I’m at:

1. PBU and auxiliary pump are relatively new and working.
2. The inputs to the Klima socket have the correct values per Saumil Patel’s 50 item test.
3. The compressor will engage when I jumper sockets 5 and 7 at the Klima relay. Cool air will blow, but the wires get hot.
4. Currently, I have an “ice cube” relay installed in place of the Klima (trying to narrow this down).
5. I removed the connector at the compressor and hooked up just the wire for the clutch control output (blue/green). Probably doesn’t affect much since I’m using the “ice cube”, but I wanted to eliminate as much as possible. With a 30 amp fuse, the A/C works fine (just ran for several seconds to verify). 15 amp fuse will blow.
6. Now… I noticed that one of the wires that go to the speed sensor on the back of the compressor is exposed and a bit frayed. I did some continuity testing and neither wire seems to go to ground. Also, when I tested across pins 9 and 11 at the relay, I got 650 ohms resistance and .3 volts when I engaged the compressor, which seems to be correct for the speed sensor (prior to pulling connector at compressor).

Does anyone know if there is a way to disconnect the speed sensor at the compressor in order to take that out of the equation completely? Also, am I on the right track in thinking that there is an electrical problem at the compressor, or should I be testing somewhere else as well?

Thanks in advance for any help. I'm out of ideas.

you need a new/reman a/c compressor clutch..shouldn't blow a 5A fuse let alone a 15A.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Doc,

Is it possible to fix just the clutch, or would a sane person just replace the whole compressor (it's 4 years old)?

Thanks for the reply.

Yes, it is the compressor clutch coil. The speed sensor can only affect the controls within Klima, not the side of the relay contacts from where this large amount of current is flowing. Some compressor rebuilders can rebuild just the clutch for you.

__________________
Saumil S. Patel

Excellent. Thanks Saumil.

MB dealers offer a reman clutch for MOST MB applications... $150

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Clutch can be replaced without disconnecting the compressor from the refrigerant lines.

__________________
I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

as long as the same clutch is available. Specially if the compressor is not the original.

__________________
J.H.
'86 300E

I'm checking mine tonight, suspect I'll be ordering a clutch tomorrow.

The clutch is the same on most Nippondenso compressors, and all models that age use a 10P15, I think.

(edit)

Just got home from testing the compressor clutch coil -- draws more than 10A! Ordering a new one tomorrow.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Peter,

What happened with your clutch? Will you try the repair yourself? (just saw your update... please post the results when fixed. thanks)

Mines fixed and blowing cool again. I paid someone to fix it because the Texas heat was getting to me. All the diagnostic legwork paid off and I was able to just fix the clutch. Thanks everyone for your comments.