I turn on the AC, and I'm not able to diagnose any problems because the clutch doesn't even engage. Ambient temperature and engine temperature are not factors...it just doesn't engage, period. Any suggestions as to where I should start looking? Thanks for your help, all.

BTW - sorry to be asking a question that's been asked 100 times before - I love brickboard, but the search function is atrocious!

If the clutch does not engage when you jump the prssure switch, use a 12 volt test light to check for power at the connector that attached to the compressor clutch. With the engine running and the connector disconnected, attach the clip on the test light to ground, and touch the probe to the wire in the connector on the power source side of the connection. If it lights, the problem is in the clutch, if it does not light, you have to trace the circuit back and find out where there is power and where there is not.

I would bypass the pressure switch to see if the clutch is capable of running, briefly. Then (if the compressor runs) you need gauges to recharge it.

Very good - that's just where I'll start. The pressure switch is located directly on the compressor, yes? Or on one of the lines close to the firewall? Or?

the pressostat(low pressure switch) is by the dryer/accumulator.
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'88 240, '92 745, '98 v70 -John, Tampa Bay

Yes, passenger side firewall, as I recall.

Just now getting around to fixing this. I specifically remember reading about how to do this about a year ago, and I vaguely remember how it went, but I never did it, and I'm not having any luck searching the archives.

How exactly does one go about bypassing the pressure switch?

Pull off the switch from the low pressure line, close to the firewall. Take a piece of wire and jump the two leads on the switch. If the compressor engages, plug the switch back in and plan to add a can of r134a.
OR you could just get a pressure gauge for the AC and see that the pressure is low and add the required amount of r134a, but NEVER more than 2 cans! The system only holds 26oz total.

Klaus
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(V♂LV♂s 1995 854T, 1998 V70R)