4ks AC question - general and clutch

[Roger Albert]

Hi guys

I had my AC set up with new R134 compressor, expansion
valve, and and new rec/dryer last year.
It has become marginal, conveniently a few weeks after
warranty expiration.

If I read low side, I get about 50psi @ 95F) (lower than
some typical values, a bit higher than Audi spec.)  It's
close, so I'll call that good.  The high side value is
similar.  About 200 is well within the range of 100-300
quoted by Audi, though w/o ref to temperature.  Aftermarket
books imply the 95 degrees ambient temp should have yielded
about 250 psi, so I am probably a bit low.  Any ideas or
comments pro or con?

Still, the system wouldn't take any more coolant.  Seems to
be at the right level, but the air is now only cool, not
cold as in the past (it was never exactly icey)

While doing the measurement, I noticed a curious (to me) and
consistent repeatable phemonmenom. The high side port would
read about 200 at idle and creep to 225 with revving. 
However, whenever the radiator fans kicked on, the low side
reading would drop towards 180.

What could cause this.  An electrical load causing a weak
electric compressor clutch to slip? I can't imagine any
other interaction avenue, but I'm also not particularly 'up'
on AC operation.  Just learning.

So, if anyone has hard info on expected pressures or what
the radiator fan / compressor interaction might be, I'm all
ears.  Thankful ones.

Thanks
Roger Albert
Austin, TX
4ks 944 ElCamino 6bikes