I bought a used pump and switch at a junkyard for around $5 each. Working fine. Entry level repair, but very fiddly removing the pump because of awkward bolts. I took the bracket too, which made things easier.

 

Now that I have the new Hella pump fitted and it works correctly I decided to have a look at the original pump to see if it was salvageable.

3xT10 Torx screws hold the top-cap down, one came out the other two were too rusted and the Torx just turned in the head so a set of Mole-Grips managed to remove the screws, once removed I put them into the vice and I cut a straight slot in the screw-head to allow me to reuse them.

Once the top-cap was off it was apparent water ingress (possibly condensation) was the issue, the entire inners were covered in white powdered alloy oxidation (sorry no pics). I removed the top plate 3xT10 Torx, removed the impeller and barrel. The bottom plate was so crammed with oxidisation between the motor body and plate that the plate would not sit correctly.

With the top compressor parts removed I connected the motor to a battery and the motor spun freely so I knew the compressor section was the problem. I took a Stanley blade and removed as much oxidisation as possible from the alloy motor body paying particular attention to the area between the motor body and compressor bottom plate. The impeller blades were seized in their holder so they were removed and cleaned off and now move freely. I cleaned everything with isopropyl and rebuilt the pump, I'm not sure if there should be any lube in the compressor, it didn't look like anything was originally there from new. I connected it to a battery and it is now working fine. I've ordered a new O-ring to seal the top-cap as the original was badly damaged and came off in bits.

From what I've read the main problem with these pumps is the switch breaks causing the motor to run and seize. If like me your switch is good then it just might be alloy oxidisation inside the compressor causing your issue and following the above could save you the cost of a new pump.

 

The new O-ring for the top cap seal arrived this morning which allowed me to rebuild the pump now that the internals are clean. Once connected to a battery it fired up and is working as it should pulling a good vacuum. Now stored in my parts shelf for future use.

 

O-ring ID/OD, part number, URL, anything?

 

@ vtl: I fitted a 62mm x 1.5mm O-ring bought from eBay

 

Out of curiosity, do you think the pump would still work if connected reverse polarity...
I don't mean on the car but on the workbench.
I seem to recall a YT video where the polarity was reversed and it blew air rather than a vacuum.
I tried testing my 2007 xc70 pump this way, just to see but the motor jammed. I opened up the part holding the blades and found the blade holder was all smashed to smithereens.
I don't know if it got busted when I reversed to polarity or it was already broken prior to that....

 

The motor is a simple 12v DC motor and therefore on a bench it would just run backwards if the polarity was reversed. Being that the blades are at an angle it would put extra strain on the motor. I'm not sure if that would be enough to cause damage but I wouldn't have thought so if the power was only applied for a moment

 

Yes, I'd need to get hold of another old unit to be able to test it out...
In my mind I'm telling myself that the impleer blade holder must have been already busted but there's that bit of doubt...

 

I have my old pump here but I really don't want to reverse polarity it just to find out. My motor worked perfectly but the impeller blades were furred up with road salt getting into the unit, probably from the worn O-ring, once stripped and cleaned it works fine, just wish I'd done that before buying a replacement

 

Btw, ebay has aftermarket pumps for like $63.