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I have a 2003 Chevy Trailblazer EXT with rear A/C.  This year, I noticed that my A/C was not very cold and decided to reclaim the system and recharge it.  I placed three cans for a total of about 2.6 lbs worth into the system yesterday  (This is the proper amount according to the manual).  The low side indicated 40 psi and the high side indicated 150 psi.  The air coming out of the center vent was only 68 degrees with an ambient temperature of 83 degrees.

Today, the temperature of the air coming out of the center vent was 79 degrees so I hooked my gauges back up to the system.  The pressures read 80 psi on the low side and 90 on the high side.  This time I heard a loud metallic clicking or tapping sound coming from the compressor area andthe clutch was engaged.  The clicking went away once the low side dropped below 60 psi. I had the system reclaimed again and all of the air coming out of the system was warm with no indication of any freon in it.  

What could possibly be the problem?

A new compressor costs $498 so I am trying all avenues before buying this part.

Thank you,

Dave