How to fix problem with 2010 Mazda 5 (3) air conditioner magnetic clutch

The aircon in my Mazda 5 from 2010 is periodically failing. This has been going on for 3 years now. My mechanic had checked the fluid level twice and eventually told me I need a complete new compressor costing DKK5800 = USD850. Since I would loose a lot of money anyway, I decided to inspect the problem myself and I ended up saving a bunch of money.

Step-by-step instructions

Identifying the problem

The aircondition is under normal conditions not running permanently, but it is running in intervals, e.g. on for 10s and then off for a similar amount of time.
On colder days, the 'on' period will be relatively shorter. On hot days, the 'on' period will be relatively longer - ultimately permanently on.

The magnetic clutch and the fan

When the aircon computer signals 'on', the magnetic clutch will engage and thereby activate the aircon compressor.
Whenever the magnetic clutch is engaged, the cooling fan is also activated (at least on my Mazda)
When leaving my the car in idle for around 15 minutes, the aircon suddenly stops working:
The magnetic clutch stops engaging, though the computer is telling it to activate (see oscilloscope dump)
The cooling fan is permanently on, suggesting that the clutch should also be engaged, which it obviously is not.
Stopping the car, and letting it cool down for a while (30 minutes?) will normally make the magnetic clutch engage again.

Testing the hypothesis

So the suspission is, that the clutch is actually activated by the aircon computer, but for some reason the clutch is unable to engage.
By turning front wheels, it is possible to partly see the magnetic clutch (it is in the red circle on the photo).
With a small stick (I used a bamboo stick) I can carefully, but firmly, poke the clutch, and thereby helping it to engage. Be careful - there are a lot of moving parts in there...
Shortly after the clutch is engaged and cooling is ongoing, the aircon computer will release the clutch again (like during normal operation)
Next time the aircon computer tries to engage the clutch, it will fail. Again it is necessary to poke it with the stick, to make it engage.
The above indicates that something is obstructing the normal operation of the magnetic clutch.

Is the magnetic clutch stuck?

The magnetic clutch should apparently be able to move a little when you pull/push it with your hands - mine is completely stuck. This video demonstrates this, and it also demonstrates the "poking with a stick" trick. https://www.youtube.com/watch?v=Hqp9IJ2ivl4&feature=youtu.be
To get better access to the magnetic clutch, lift up the car and remove the right hand front wheel. Place the wheel under the car as a safety precaution.
Behind the brake disc you can see a plastic shield that is easily removed to access the clutch

Getting access to the magnetic clutch

Remove the 4-5 screws holding the plastic shield covering the magnetic clutch
Unscrew the bolt in the center of the magnetic clutch. You will need to hold a screwdriver like in the picture while you loosen the bolt

I am completely unable to move the clutch plate with my fingers. I used some scrap metal pieces to gradually force the plate free.
NOTICE: later I discovered that a bolt can actually be fitted (see pictures for the next step)
Gently hammer on the clutch plate top and bottom, while carefully forcing scrap metal in behind the clutch plate.
Applying some WD40 did not seem to make much difference, but you can give it a try.

Though it took a bit of brute force to get the plate free, it did not suffer any visible damage. You can barely see the shims inside - be careful not to loose them.
It was only after I got the plate loosened, that I noticed that it is actually threaded to allow a bolt being screwed in. This could probably have been handy when loosening the clutch plate.

Be careful to get the shims out, so they are not accidentally lost. My clutch had 2 shims.
Inside the clutch plate, I could see bits of green/corroded debris.

Clean out all visible debris from clutch plate and the clutch itself.

Microscope (4x) view of the debris. I cannot tell where it originates from.

After cleaning everything carefully, I also sanded the two parts a bit, and applied a bit of grease.
Verify that the clutch plate can now move back and forth easily.
Assemble everything again, and now you can hopefully enjoy a working aircon, that does not stop working while you are driving.

Conclusion

To reassemble your device, follow these instructions in reverse order.

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