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  #1  
Old 08-31-2018, 01:51 PM
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W123 AC Compressor Relay Harness?

Anyone ever heard of doing this? Got any info on how to wire it??

My #8 fuse keeps popping, even with a 20A fuse installed and a new blower motor. I can run my blower all day, but once the AC comp kicks on it pops the fuse.

My mechanic recommended adding another ground to the compressor and doing this relay harness mod. Can't find much info on how to wire it though.

I know there's a 2 prong solenoid on the AC comp and there's an ice cube relay for it atop the driver's wheelwell. Not sure exactly how they work...
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Old 08-31-2018, 02:15 PM
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What year is the car?
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'85 300D Cal 280,000 miles
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Old 08-31-2018, 02:22 PM
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Blowing a 20A fuse means you have a shorted wire or component (clutch coil) somewhere. Time to find a new mechanic. If you've been repeatedly trying to run it with a short like that, you may have some melted wiring to tidy up now.

Fuses blow for a reason. A poor ground is not one of them. Overload of the circuit or short circuits blow fuses.
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Old 08-31-2018, 11:51 PM
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83' 300d turbo.

Any idea how to test the clutch coil?
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Old 09-01-2018, 11:27 AM
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Probe the pins with a multimeter set to ohms. Not sure what the normal value is on them, I'd expect them to be higher than 3-4Ω
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Old 09-01-2018, 01:48 PM
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Are you referring to the 2 prong connector on the AC compressor?
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Old 09-01-2018, 03:07 PM
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Yes.
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  #8  
Old 09-01-2018, 08:52 PM
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Relay

I produce these. The thread is in my signature. They are $30 + shipping. If you are using the R4, you will need the adapter for an additional $2, or make it yourself.
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Old 09-03-2018, 08:59 PM
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Does about 18 ohms sound about right? Or... is this a fuse popper?? Enough to pop fuses in addition to the blower motor?

My brand new URO blower motor draws 15A on a 16A circuit already...

Plus, I checked my battery voltage, then i probed between battery + and the AC comp body. Seems that i have a 0.25V voltage drop at the AC comp.
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Old 09-03-2018, 09:17 PM
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18Ω sounds a bit high actually. On a 12V system, that's less than an amp.
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Old 09-03-2018, 09:21 PM
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Should i replace the AC clutch coil??

Maybe it's slightly high, then causes the 20A fuse to pop after a few minutes? Perhaps there's a 1-2A of resistance in dirty contacts, old wires, etc?
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Old 09-03-2018, 10:16 PM
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Amperage is a flow of current. Resistance resists current flow, thus "dirty contacts" or "old wires" would reduce current flow, not increase it. You likely have a wire rubbed through and shorting against something. That'll cause a fuse to blow immediately.
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