A/C weirdness

[Elliott Potter]

Well, the air conditioner in my 90 is broken, again.  A bit more than a
year ago the dealer replaced the bulk of the A/C system (compressor,
dryer, ++) after the original one started failing.  
The new compressor immediately started making an awful grinding sound; I
took it there once and was told that it was overcharged; they 'fixed' it
and it was marginally quiet for a couple of days and then got worse than
ever.  Took it back, and they said maybe it needs some more oil -- flush
and recharge and sent me on my way.  Same problem.  Took it back again,
and was told that (seriously) my ignition switch was sticking slightly,
and that was making the radiator fans not come on (though, inexplicably,
the A/C did come on), so I was running high head pressure and that was
the problem.  He stuck to this story even after I showed him that the
compressor *and* the fans come on, and the key really doesn't stick
unless you try very hard.

So last weekend, when I turned on the car, I was shocked to find that
the compressor had stopped making the noise and was now purring smoothly
and quietly.  However it also stopped cooling!  I've scheduled the car
to go back on Friday, and they're going to have some other incompetent
boob try to figure out what's wrong with the damn thing; it seems like
it might have barfed its R134, but I thought it would cut itself off if
that happened, and the compressor still comes on.

Any thoughts on this?  7 years the thing's been broken, I'd like to get
it done right this time.

Thanks,
--
Elliott