A/C 101

[Kneale Brownson]

I hook my newly acquired A/C gauge set up to the 200q20v, which has not had
good cooling lately, and the gauge for the low pressure side shows about 60
pounds.  The gauge for the high pressure side shows ZERO.  When the A/C is
running, the clutch cycles on and off every few seconds and the low
pressure gauge drops from 60 to maybe 25 and then goes back up.  The high
side doesn't change.  I presume I still have a charge (I'm using
Envirosafe's R12 substitute).  What don't I have?