Noticed in last few times I drove car with AC on didn't seem as icy as usual. Was going to check the pressures, but now compressor won't engage. My electrics are good from AC switch/HVAC head to the compressor. Low pressure port pressure is high while compressor quiescent.

I'm to old for this.
Roger if you see this expect a call soon.

 

Go through a little troubleshooting to see where the break is in the compressor power supply. Easiest first access is at the freeze switch, mounted under the plastic cowl cover base of the windshield top end of the hood. Small box with two wire connections on it, plus a small capillary tube that routes into the airbox and the evaporator. Disconnect the two wires from the switch. Test each wire with a DC volt meter. With key ON, AC ON, you should see battery voltage at one of those wires referenced to ground. Nothing on the other wire. If not, work your way towards the control head to find the fault. If yes, reconnect the two wires to teh freeze switch and test again with the wires connected. Both should show battery voltage referenced to ground. If only one shows voltage, the freeze switch is open and needs to be replaced. If neither show battery voltage now, it's likely that the clutch relay in the control head is failing. If battery voltage at both, continue. Turn the key to OFF.

The system pressure safety switch is mounted on the tubing manifold by the receiver-drier in front of the AC condenser. On the top of that manifold is a transducer for fan controls, on the bottom is the switch. Remove the connector on the switch. Using your meter set to Ohms or continuity, test the switch for almost-zero Ohms to verify that the switch is closed. If no continuity or not close to zero Ohms, the switch is telling you that your refrigerant pressure is low, and is protecting the compressor. You can verify the too-low system pressure with your gauge set.

 

dr bob, my electrical circuitry is slightly different than factory since I put in a DC Control fan control system. This was worked on in a thread some time back. I had carefully logged all work in my maintenance log which I referred to today. My engine cooling and AC systems had been working well on this system since installing almost two years ago.
With engine on I have 14 V at freeze switch, low pressure switch, and at line to compressor.
I took a quick look and the pressure is high at the low pressure port.
It could be a clutch failure, but at this point if I remove the compressor I'm going to replace it.
I'm to old and don't have time to rebuild it myself. It is a Porsche installed r 134 compressor.

 

Is the 14V at the compressor terminal with all the wires connected? The failing control head relay passes battery voltage OK when the laod at the end of the wire is just the meter. Put the load from the clutch coil (4-5 Amps) on the end of that as you measure. If there's resistance in the circuit, typical to a failing relay contact, the voltage you see will be much lower.