A/C - typical pressures on low side?

["Creel, Kenneth" <kenneth.e.creel@lmco.com>]

I recently had my A/C recharged at Wal-Mart ($25/lb, thanks to whoever
posted).  The system only had 0.6 lb in it.  That was removed, the system
vacuum tested, and 2.25 lb added.  I watched the entire procedure.  The
tech had problems disconnecting the high pressure hose and R-12 was
spraying everywhere.  I protested, but he said "it's coming out of the
machine."  It was a cool day, and the A/C seemed to work.  Hot days since
then disprove this.

I went through the Bentley diagnostic procedure.  Except at idle, the low
pressure switch is turning the compressor off after only 5-10 sec. of
operation.  Low pressure side, w/ engine off: 90 psi.  A/C running on "LO"
@ idle, the pressure hovers just above 20 psi, and the compressor runs
continuously.  If I raise the engine idle, the pressure cycles between 70
and  <20psi (where the compressor shuts off).  I didn't explicitly test the
low pressure switch, assuming that it is turning off the compressor @ 17
psi, where it should.    The coldest air I've seen from the dash vents is 13C.

The Bentley flowcharts suggest either "low refrigerant charge", or "replace
restrictor."  For obvious reasons, I suspect the former.  Can someone give
me an idea of what pressures I should see in a properly charged system?      

Thanks,
Ken Creel
'90 90q20V
Denver