Although I know that you mean well with all this reported info, the simple fact of the matter is that some here might find it misleading in that the #1 known AC problem with 850s is not the compressor itself but simply that the system becomes low on freon.
The first thing anyone should have done whenever desiring to get their faulty AC system repaired is to know the present freon charge and the only way to do that is to use a recovery machine as those weight the actual amount of freon removed from the system. 99.9% of the time, one will find that the 850 with poor AC performance (IF it's even working at all) is due to it being low on freon.
Being that you can't read high side pressure with a guage, using a guage on the low side only can be misleading.
Short of bad seals leaking freon or oil (not common), I have yet to see a bad 850 AC compressor.
Although stones can puncture condensors or a line can crack (rare), the #1 source for freon leaks in 850s is the evaporator as often discussed here.
If there's an electrical problem such as a pressure switch or voltage supply problem to a switch, that'd be best diagnosed with the correct wiring manual but AC electrical problems are also fairly rare with 850s.
Start any AC diagnosis by knowing the systems freon amount (weight) as it should be 1.65 lbs, not much less than that or it won't function correctly. Only a shop certified for AC repairs would have a recovery machine as they're not cheap and the average shop labor time to recover, recharge, add dye (highly advised) is 1 hours labor.
Until one knows that the systems charge is full, you'll be doing alot of guessing otherwise and you'll most likely guess wrong if you think the car has bad parts. Just a "heads up" on this from a guy with ALOT of AC experience and certifications.