So I have a turbo import
 
Air con isnt working
 
The switch etc on the climate control panel works and lights up  however it doesnt engage the compressor pump - it doesnt turn on
 
any suggestion - a relay somewhere or a fuse ?
 
wiring at the compressor is okay

You could be out of gas. The compressor won't turn on if there's no gas in the system.

robk
You could be out of gas. The compressor won't turn on if there's no gas in the system.

okay yes there is no gas I believe as just finished installing the rev3 engine
 
so I will advise this to the workshop
 
how does the compressor sense this ?

it has a pressure check valve. If rail presssure is too low it won't turn the compressor on.

Air conditioning systems run pressure switches in the gas lines to detect the system high and low pressures. 

 The paperwork from the workshop shows they recharged the system when the rev3 engine was put in

If you have a slight leak, you loose the gas and the pressure drop doesnt allow the system to come on. Its happened to me twice.  The brand new valves at the front of the car where they put in the gas, they leaked. Second time found to be a joint in the aircon pipes under the car.
Check that the wire going to the air compressor is grounding when the air con switch is on - you should hear the air con clutch kick in.  If its not, possible fuse or your low on gas.
Check that the idle increases when you turn the air con on.
Best of luck,