Help! F355 air con issue. Compressor not engaging.

Hi Guys,
I have also posted this in the 348/355 section but hope one of you technical guys can spare some time to point me in the right direction.

I have only just purchased the car so do not know the history. Bought the car with air con not working. Everything appears to be working but not getting cold air and compressor not engaging (couldn't hear clutch engage). Took the car to an air conditioner specialist who discovered the Hi and Low pressure charge valves under the front carpet had been leaking. The system only had 40g of gas left in it. System was drained and vac'ed and pressure tested all ok. Then 800g of R134A was added as per spec.

However the AC compressor will still not engage. System is fully charged with no leaks. We have diagnosed the main fault as no power being fed to the compressor by checking for power physically at the compressor itself (bottom connector next to the compressor, access from under the car). Checked this +ve supply wire to switch on compressor and this has 0V, (obviously checking this with the STOP button out and AC system fully on)

The car recently had an engine out belt service prior to my ownership and I'm wondering if there is any connector in the engine bay that connects the compressor that needs to be removed prior to engine removal and if so perhaps this has not been reconnected?

If not are there any other little issues that may cause the compressor to not receive an "on" signal from the ECU?

We have also undertaked the following tests (all tests conducted with system temp set to max cold and fan on full).

1) Compressor clutch engages when 12V +ve is applied straight from the alternator +ve. Which indicates the compressor is ok. (wanted to just test the clutch to see if it engages when power is applied to the wire and it does)
2) All fans operate at every setting ok. When all set to Auto the system switches off when the STOP button is depressed (which I believe is correct) and the STOP button then lights up green. Once STOP button is released the fans come on full speed in an attempt to auto cool.
3) AC fuse in the passenger footwell checked and ok. Also checked the separate fuse under the carpet and both relays attached to the air intake box checked (1 for compressor and 1 for fan).
4) Checked the pressure switch at dehyrator filter. A +ve voltage is detected and is switched via the stop button (IE STOP button depressed no voltage, button out voltage detected.

I really appreciate any assistance or idea's on this.

 

Just been thinking and does anyone know where the signal originates to switch on the compressor? I'm assuming it comes out of an ECU somewhere..... If I knew where that was I could put a VM on it to test for output.

 

Since I am getting good response from the 348/355 forum I will close this thread and kindly ask anyone who can help to respond on the 348/355 forum?

Assistance greatly appreciated.

Latest is that the loom plug at the rear of the left rear shock in the engine bay is indeed switching and supplying power. However this then loops off into a Bosch relay. All info is in my last post in the 348/355 form.

Basically I'm interested in seeing if the relay has been wired up correctly. Once again assistance greatly appreciated.