Help me cool my wife down. With the A/C in her Mazda 5.

The wifemobile is a 2013 Mazda 5 and I have confirmed that the A/C clutch is not drawing any power at all.  I have power at the A/C relay.  When I jump that relay, I get power at the connector, but it draws zero amps.  Connecting +12V straight to the connector does not snap the clutch.  So I think I can rule out the pressure switch - there is pressure in the system according to my gauges - the fuses, the relay, and the wiring.  I am also hearing a somewhat faint knock-knock noise that I think is coming from the accessory side of the engine, but I can't quite narrow it down.  The A/C pulley does look like it has a tiny bit of wobble at speed, though.  I was all ready to order up a new pulley, clutch, and coil kit from Mazda - no aftermarket options there, which is weird - but then I started thinking about it a little.  The clutch coil has a little thermal switch on it and a new coil comes with a new switch.  Where it's all located right now, I can't see how I can easily check that switch but I would think that if the coil is pulling zero amps, that would almost have to be the source of the problem. 

Is that switch a fuse?  By that I mean, when it gets too hot does it blow and then have to be replaced or will it reset itself once things cool down?

How common is it for that switch to just go bad?

I guess the question I'm really asking is this:  It appears to be a complete pain in the kiester to get to the compressor clutch to R&R it.  Is this likely to be a failing compressor that got too hot which is going to either just pop another thermal switch and/or explode gloriously into the condenser and evaporator?  Or is more likely that it's a failing pulley bearing that might have gotten things too hot?  Or did I have a failing pulley bearing and that switch just pooped in its shoes at more or less the same time?  I'd rather not spend $350 on the clutch & coil assembly just to have to turn around and replace it right away.

I would guess it needs a new field coil.

Do you have a way to check what the resistance is supposed to be? You could check it without disassembling anything.

I have swapped a couple on a Honda and it was doable by just unbolting the compressor but without disconnecting the lines. You need a good set of snap ring pliers and a way to hold the pulley if you don't have an impact.

I know its not the same car, but this might come in handy:

https://acurazine.com/forums/1g-rdx-diy-faq-161/diy-replacing-field-coil-air-conditioning-compressor-862720/

An entire new Denso compressor is less than $300 from rock auto fyi.

I've done a couple coils in the past so that doesn't really scare me at all.  I'm not entirely sure how to get to the snap rings - I might need to unmount the compressor and let it hang or something - but that's a minor detail that I'll figure out later.

The reason that I'm 90% sure that it's the thermal switch is that I get infinite resistance on the coil.  So either it has come completely apart internally or that thermal switch is interrupting the circuit.  I'll also leave the possibility that a wire has broken, but if it has, I can't see it from the vantage point that I've got.  Without starting to pull it apart, however, I cannot get to that switch to test it.

If that switch is a one-and-done switch, then whatever caused it to pop could still be a problem.  If it's self-resetting, then perhaps the switch itself has failed and replacing it (as part of the coil assembly) will take care of it and I won't have any further carnage.  If that switch is just one of those things that just fails from time to time, then no big deal.  That's what I'm trying to figure out here.

I saw the Denso compressor...  What I find weird is that that compressor obviously comes with a clutch and coil.  But they don't sell it separately.  I actually considered buying one of the cheaper compressors they have for sale, taking the pulley, clutch, and coil off, and throwing the compressor away.  Also, I'd rather not have to take the car somewhere to have the system evacuated and then replace the dryer and everything if the compressor is fine.

wae said:

I saw the Denso compressor...  What I find weird is that that compressor obviously comes with a clutch and coil.  But they don't sell it separately.  I actually considered buying one of the cheaper compressors they have for sale, taking the pulley, clutch, and coil off, and throwing the compressor away.  Also, I'd rather not have to take the car somewhere to have the system evacuated and then replace the dryer and everything if the compressor is fine.

In reply to Slippery :

Yeah, I've got all those PNs.  What I thought was weird is how I can get a Denso compressor but no aftermarket coil, clutch, or pulley.  The only option for those is OEM Mazda.

Ahh, got it.

Yeah, I had the same problem with the Honda parts. Had to go through the dealer.

Well, berkeley.

Finally had time to screw with this.  Got the old clutch coil removed and thought it best to try to turn the compressor by hand before I put everything back together.  It appears to be locked up tight. 

Sucks to have to open the system, but at least you know what the problem was. 

When I saw the first post, my thought was "the last two compressors I did for an open clutch failed because the clutch melted trying to turn a seized compressor".

Lazy man's way to check the coil is an ohmmeter between the relay socket and the battery negative.  It should be in the single ohms range, maybe low double digits.  Fried coils will be way higher or open.  What's nice about this is it tests the entire circuit.  It's still good to go right to the connector at the compressor and check again, to verify that it's the same as that full circuit reading and not a wiring issue.  But it's rarely a wiring issue.

In reply to Pete. (l33t FS) :

Yeah, until this one I had done exactly two and was 50/50 on just coil. 

I ordered up a compressor, condenser, and expansion valve but the process of removing the pulley seems to have toasted the bearing, so rather than put the new OEM pulley on, I'm just going to let the car sit until next week when stuff comes in.