Ac problems

What would be causing ac compressor to knock off when running causing ac control knob to flash

 

Slipping belt; bad belt tensioner, water or oil on the belt or pulleys, glazed or worn out belt.

 

Does the compressor turn on for a few seconds and then turn off with a flashing A/C light?

The flashing A/C light is when the A/C amplifier does not detect a speed signal from the compressor lock sensor after commanding the MG CLT relay on.
Possible causes are:
Open or shorted wire(s) in the lock sensor circuit
Bad lock sensor
Internal problem in the compressor
Open or shorted wire(s) to the MG CLT relay
Open in the wire from the MG CLT relay to the compressor
Failed compressor clutch
Belt slipping
Failed A/C amplifier

You will need to check your wiring
The MG CLT relay should have power on pins 2 and 5 when the ignition switch is on, the A/C amplifier grounds pin 1 to turn it on.
You can momentarily jump pins 3 and 5 of the relay to see if the clutch engages.
Also check the wiring between the lock sensor and A/C amplifier.
The sensor signal itself can only be effectively checked with an oscilloscope.

 

@Dm93 - Great diagrams for reference. I saved those.

My similar situation was unfortunately a bad, seized compressor as I thought. In my case the engine bogged down, then I smelled burning rubber. I pulled the Air Conditioning fuse (#1, upper left) so the compressor wouldn't engage on another HVAC setting, such as the dash toward the windshield. Had the compressor and serpentine belt replaced last week.