My issue is i charged my ac with r134a as requried 4 months ago before this rediculous heat wave engand it worked great through spring... now i can't get the clutch to engage. First it was a loose relay so i got one from Advanced auto today with no change. What gets me in "Max", "Norm", "Bi-level" and "Defrost" the engine idles up as commanded by the ecm as if the clutch is engaged. Now if i go unplug the small sensor (probably a pressure switch) along the line coming out the accumulator idle comes back to normal but of course during that the clutch never engaged.

 

You can jump a wire to the compressor to see if it engages. If it doesn't, then the clutch itself is likely the culprit.
Refer to wire diagrams of your car to find proper polarity and pinouts.

 

Got rid of that headache two wires on the relay have to touch to get it to function properly but could use a little bit more freon.

 

Check for voltage between the 2 wires on the A/C clutch. Should be 12V with the A/C switched on. If not, you still have wiring issues. If it does, the clutch on the compressor is shot.

 

Also double check the ground to the clutch, don't just assume because you have power from the hot wire that the ground is working. Just because the compressor should be grounding through the casing doesn't mean the clutch is getting a good ground. But you could have a failed clutch.