Richard Armstrong

I do most of the 928 A/C refurbs here in the UK and have rebuilt about 25 6E 171 and 10PA20 compressors over the years. Some come in with burned clutches and it although it is difficult to say whether it is the coil shorting or the pulley bearing failing, IMHO it is the pulley bearing which goes and then takes the insulation off the coil, then it shorts, gets hot,and all hell is let loose. The front plate to pulley gap is not critical to 0.1 mm as someone has suggested. The only coil I have had back that has burned out on a refurb was due to bearing failure, and that was one of the extremely rare times I didn't change the bearing as I knew it came from another unit which broke a valve vane after a couple of months. It went out perfect and failed within a few miles. Can't explain it.
The Usual cause of bearing failure is overtightening belts, and the 10PA has a smaller bearing than the 6E. I also put an in line fuse in the connector to the compressor to protect the controller relay.

Richard

Bill Ball

Richard:

Thanks for those comments. What size fuse did you use?

Alan

Bill,
Don't know what Richard used but 10A-15A should be fine - I believe the clutch is about 8A steady state but has a turn on spike. The total circuit including the HVAC & Blower fan is 30A via fuse 20.

If you were to do this - per my previous suggestion - you can also add the fuse on CE - there are always spare fuse slots for every year (but always check the internal fuse bussing - on S4+ some are connected to adjacent circuits inside the 5 circuit fuse blocks... Much easier to keep them dry, check and change in this location (even with a lift!).

Alan

Richard Armstrong

Yup I use 10amp.
Wiring to the board is obviously neat, but a lot of hassle, whereas the connector is right there at the front of the engine. I bought a load of blade fuse in line rubber covered waterproof fuseholders and connect one up and tuck it out of the way using cable ties.

Alan

Yes agree - but if you see the notes earlier Bill has a burned out relay or in the AC head unit (or 2) and one proposal to avoid this (its a known weak point - the relay contact are not capable enough anyway) is to add a standard STST relay to drive the clutch on the CE panel (its a giant pain either way). If you are already into the panel - its very little extra work to add the fuse - wouldn't propose it otherwise.

Alan

Bill Ball

Dave, Dan and Rob win the Golden Freon Can Award.

I just got the new compressor. I went to drain the oil out of the old one --- it didn't have any. The compressor still turned, but it appears it labored enough to overload the clutch and burn it out, as the guys all suggested. I never had occasion to crack open and check the compressor and usually the installed oil remains in the compressor. Argh!

Anyway, the shorting of the AC clutch power line burned through a trace in the headunit board. I soldered over that and everything appears to be in order...well, almost.

The rear AC blows very cold, but the front is warm. We had this symptom sporadically before. So, I'll replace the front expansion valve and recharge (R-134). That should do it.

Thanks for the suggestions and especially about being suspicious of the compressor when AC clutches burn up.

worf928

Clean the evap, check vacuum to the heater valve.

But you knew that already.

I myself am waiting on a compressor... <insert foot tapping smilie>

I don't know about you but, I've decided I don't like A/C work.

Bill Ball

Hi Dave:

Those are good general suggestions. I did clean the evaporator when I replaced the resistor pack. The heater valve appears OK as the front vent is not warm with the AC off blowing ambient air. It just doesn't get any cooler with the AC on. Already have the expansion valve bolts out and will replace it in the morning.

Over all I don't like AC work either, but I just bought a Snap-On R-12 recycling machine that looks brand new for $200... and it came with 50 lbs (not 30, but 50) of virgin R-12. Couldn't pass it up. I like AC work better than electrical. The AC system is rather straightforward.

worf928

Like I said: you knew that already

Good luck.

worf928

Holly $h1+. I missed that at the first read.

Damn. You basically bought some R-12 (on the cheap) that came with a free recycling machine.

Can you say SCORE!?

IcemanG17

Bill
Just because the heater valve holds vaccum doesn't mean its not leaking.....I've had TWO that did this...help vacuum just fine but still passed hot water...one was a stock unit with a failing seal and the other was the all metal version......both did exactly what you have noticed

Another less likely option is the adjustment of the flaps inside the main HVAC unit...possibly the setting motor is dead and stuck at the heat position? Are you sure it works?

Bill Ball

Brian:

Oh, yes, I have had the experience too. When I bought my car, the vent temp was about 10-15 degrees over ambient (stick hand out sunroof/window, compare temp outside to vent). Even though the heater valve held vacuum, it was not sealing internally. New valve and the vent temp dropped to ambient.

SharkSkin

Bill's AC Shop...

zekgb

I need to make an appointment...