Problem:  Chevy Blazer S-10 Tahoe, AC when engaged puts out cold air for
about ten minutes.  Then, quits putting out cold air.
Took it down to the local garage.  They wanted to evacuate the system.  They
suspected blockage in the freon line someplace.  Suggested the low pressure
switch was defective.  Their explanations made sense to me.  But, I
hesitated.
Have a home use freon kit used last on my VW.  Bought a can of R-134.
Turned on the AC to MAX, and hooked up the kit without opening the can of
freon.  A 30 second cycle of high of 47 psi to 28 psi was noted.  When 28
psi was noted, could hear the compressor kick in.  So, opened the can of
freon.  It took about a half a can.  Max psi is now around 53 and low 31.
Am not hearing the compressor kick in at the low end of the spectrum.  The
AC doesn't quit putting out cold air now.
Don't know the mechanical or electronics behind this, but hope this helps
someone.