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How common is open circuit in magnetic clutch

gaborkiss on Sat July 09, 2011 12:28 AM User is offline

Year: 2005
Make: Scion
Model: Tc
Engine Size: 2.4L


I have a 2005 Tc with 150000 miles. My A/C stopped working a couple of days ago. I notice that the magnetic clutch is not engaging. I have applied power to the clutch lead (Scion has a connector about 8" from the compressor and I put 12V there), no good. I have tried to measure the resistance of the clutch and it appears infinite. I wonder if it is possible that the clutch itself has suddenly open-circuited. I mean, it is certainly possible, but how likely is it?

Has anyone ever encountered this? Bad ground? Broken wire? All these are possible I guess, but seem awful unlikely.


Dougflas on Sat July 09, 2011 5:11 AM User is offline

Clutch coils do open. Remove the coil and see if you can see if the coil ground is making connection. Some have a rivert that may need to be peened tighter and resoldered.

GM Tech on Sat July 09, 2011 8:04 AM User is offline

Probably a thermal fuse imbedded into face of clutch coil has blown--- they do this to prevent "walk-homes" from a seized compressor-- but the problem is that the fuse blows too soon- at a lesser temp then safety I had a Kia Sedonna that went thru two coils in 9 months- blowing the thermal fuse each time---warranty would have replaced that $72 coil-- but it is a 2 hr job to remove compressor-- what a PITA-- so I refuse to put the same part back on-- I mean history will repeat itself- and 9 mths from now I'll be replacing that coil again-- so I grind out the thermal fuse, and solder in a straight piece of copper wire (from house wire ground) and never have that issue again....sometimes things are over-engineered. The very thing that is designed to alleviate an issue- actually creates one......I'll take my chances on that "walk-home"

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

gaborkiss on Sat July 09, 2011 10:20 AM User is offline

Interesting, I have never heard of this thermal fuse thing before. Unfortunately I am not able to get at the compressor easily. The compressor will have to come out and that means draining the system etc. PITA as you say.

Thanks for the response. This is a great forum. I really enjoyed reading the threads about how to fill liquid.

bohica2xo on Sat July 09, 2011 10:42 AM User is offline

Sometimes you have to look at the bigger picture. It appears you drive about 25k miles a year if the mileage you listed is correct. That compressor has a lot of hours on it, and the idler bearing has made millions of revolutions...

If I had to remove that unit to replace a clutch, I would replace it with a new compressor. 330 bucks will get you a brand new unit. The parts & labor to replace a clutch, idler bearing & seal ? On a compressor with 150k on it?

New compressor & clutch, Scion Tc


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

gaborkiss on Sat July 09, 2011 11:06 AM User is offline

Yes, that's what I was planning to do. I agree it doesn't make sense to invest all that labor and not put in new parts. I'll replace the serpentine too.

Thanks for the lead on the new one. That will give me a reference point when talking to the shop.

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