Hello all!
First a little history on the AC system. About 2 1/2 yrs ago the AC drier sprung a huge leak in a line. Knowing what I knew at that time, i replaced it, added refrigerant and oil and it worked fine from that point. What I didn't know then was that I should have drawn a vacuum on the system to get moisture out and possibly added UV dye for any small leaks in the future. I believe i also undercharged the system because it takes 54 oz to fill plus 14 oz oil. I only added 18 oz refrigerant and another 12 oz that had oil already in it. Fast forward to now, The AC stopped working late summer last year but since it was going into the fall season, I didn't want to fool with it but now that my wife uses it more than me, I gotta fix it so here is what has been done so far. I confirmed the compressor is still good by applying 12V directly to it and the clutch engaged. I had the refrigerant reclaimed, put a vacuum pump on it and it held a negative vacuum for about 45 minutes with the pump off. It lost about 2 inches of vacuum but I'm not sure if it's a minor leak or the cheap gauge set. I then proceed to add refrigerant slowly while the engine is on and the AC on max and waiting for the compressor to kick on. Barely added 12oz refrigerant, Static pressure (compressor never turned on) reading on the gauges read 100 on both sides. Jumping the low pressure switch failed also. Since the AC compressor is controlled by the PCM, I figure there's a fault being picked up by it. First I confirmed no blown fuses then I used an OBDII scan tool to pull live data on the following:
ACCS - air conditioning compressor cycling switch (passed)
ACP - AC pressure switch (passed)
WAC_F - wide open throttle AC cut-off fault (passed)
WAC/ACCR - AC clutch (passed)
What I could not find a PID for that may need to be checked was ACCLT (AC clutch) and EVAP temp (ambient). I confirmed the AC clutch relay was working also by jump wire and I could feel the relay click when inserting back in. This is where I am stuck at the moment. Looking forward to the feedback....

 

The clutch relay may be clicking , but do you know if it is sending power to the clutch.
You will need a voltmeter or a test light to confirm this.
If it uses an ISO relay pins #85 & 86 activate the relay. terminal #30 should have key power all the time so that when the relay closes it sends power to terminal #87 that should go to the compressor clutch. Look under the relay panel, sometimes we find surprises there.

 

Just an update,

Apparently there is a reply that I did over 2 days ago that still hasn't posted presumably due to the need of a moderator review(?). Anyway I tested the clutch relay by swapping it with the hi-beam headlight relay. Lights still worked but no change with the headlight relay in place of the clutch relay. I'm not too sure on how to check the clutch relay but I confirmed voltage across pins 85 and 86 but no voltage from 30 to 87 with the relay removed. Checked again for blown fuses, none. All the tests were done with key on, engine running, AC on max.

 

There should be battery voltage at the socket where the #30 terminal of the relay gets inserted. It comes from a fuse in the Central Junction Box (CJB) .

 

Sorry for the lengthy delay. I'm stumped. I do appreciate your help hanky but now I'm at a loss on what to check next. Since the last post the AC clutch relay does not get power at the #30 terminal. I checked with a voltmeter and a probe to confirm. I still have power to #85 and #86 though. I also retraced my steps back to the compressor clutch. I hooked up 12v to the connector on the compressor only (disconnected it from the wire harness). The clutch engages so I turn off the voltage then turn on the engine. Turn on 12v again to the compressor and it engages and turns (drop in engine rpm also) but now the gauge readings (low/hi). Static reading is 100/100, dynamic reading is 120/130, manually cycling the compressor on and off results in the same. In addition because I already had a can of R134a hooked up to gauges, I attempted to see if the system would draw down more refrigerant. No bueno. I'm going to assume one of two things, the compressor is bad for #1 and there is a possible blockage for #2 or maybe possibly both at this point. Thirdly, I still have yet to figure out why the PCM is denying voltage to the compressor clutch circuit. I jumped the hi-pressure switch on the line and the low pressure/cycling switch at the thermal expansion block but no change. I have no plans to replace the compressor yet until I can get voltage to the clutch since it would be a waste of time to do so. Is it time to call in a professional or am I missing the forest for the trees?

 

Okay, got a few more clues. Haven't given up yet. My apologies but there is power to pin #30. Don't know how I goofed it but it's there. I also was able to get voltage to the compressor from the AC relay box under the hood. This however is not a solution but another clue in chasing down the problem. I checked the relay again and it works when I apply voltage to #85 and #86 (click) from an external source but it does not work (click) when connected back to its socket even though there is 12v there (checked and double checked). Did the same with a different relay but same result. Unless there is a huge difference in amps or polarity, I don't understand why that is happening but will eventually. It's too much to explain but I can go into detail if needed but I looked again at the back of the relay box and figured out how to apply 12v in the proper polarity across the diode to get 12v at the compressor however no clutch engagement but I can hear what I believe is another relay at the fuse box clicking when I apply power.

 

This is what I believe how the power gets to the clutch.
Power comes from a 10 amp fuse in the CJB.
that power goes to the function switch when you turn the AC on.
then that power goes to the comp cycling sw.
from there it goes to the AC hi press sw.
from there it goes to the PCM
The PCM provides the ground to activate the AC clutch relay
When the relay closes it supplies power to the mag clutch.

The AC clutch relay term 86 gets power from 20 amp fuse in CJB
Term 85 of that relay gets its ground from the PCM.
The clutch relay gets its power from the CJB to term 30 of the clutch relay.
If you remove the clutch relay, jump terminals 30 and 87 and the clutch should activate , does it? Yes/no

Once we get the power path clear, then if necessary we can check out where it is getting lost or why it is not coming out at all, we'll get it going.