There is only 12V at C4 when the compressor relay closes, which is controlled by the ECU. Try jumping the relay contact by bridging brown/white wire to the red at the AC control module to see if the compressor starts.
If it does, it could be the Trinary switch not signalling the ECU to start the compressor due to low refrigerant level or defective wiring or switch.
The fans are also controlled by the ECU and run at half speed if the compressor is running.
When jumping the relay contact, I understand that you unplug the wider connector and use some coated wire to bridge the brown/white to the red. Do you leave the other wires disconnected while attempting this?
2005 StormTi, Touring Pack,Larini F1 Exhaust,Fujita Intake,Micro Mirror