I've been spending a lot of time on my air conditioning system on the Evora lately, and I've learned a few things (the hard way) that I thought I would pass on to the community, that might (hopefully!) make things a little easier for you.
1. The Hidden Code: If your A/C system goes completely dead, whether from a faulty component or depressurization, the ECU will issue a Diagnostic Trouble Code (DTC) that prevents the system from starting back up again. Presumably, this is to protect the system from damage, not cause you to bring the car to the dealer, right?
The challenge here is that there is no visible evidence of the code - no "wrench" or "engine" light on the dashboard - so you have no idea why your compressor won't engage when you're trying to refill the system after repairs! To correct this, you need a scanner that communicates with the EOBD European protocol (CAN 11 bit, 500 kB); but even when you scan, you won't see a fault code. Go to "Delete DTCs", select "All" and delete everything. With the right tool, this will eliminate the code that is preventing your A/C from coming to life.
2. The Trinary block: Okay, the code is gone. We hook up our gauges, start the motor, open the low side, and watch the low side gauge climb to the can pressure, usually about 75-80 psi. Nothing. The clutch still does not spring to life, the high side stays at 0-10 psi. What happened?
The Evora A/C system further protects itself by shutting off if the pressure gets too low (less than 50 psi), or too high (more than 300 psi); and it does this with a pressurized switch called a Trinary switch. Thing is, the Trinary is in the HIGH side, just after the dryer - and since we are adding refrigerant to the low side, there's no pressure there yet. We need the compressor to come on to activate the Trinary, but we need to Trinary on to activate the compressor. Catch 22.
The solution to this is to shut the motor off. WITH THE MOTOR OFF (just checking
) open the high side valve on your gauges and let the high side reach the 75-80 psi can pressure. Both sides should be about equal, and over 50 psi. Now, CLOSE THE HIGH AND LOW SIDE VALVES ON YOUR GAUGES. This is important! With the gauges closed, start the motor, and this time, when you push the A/C button on the console, you should hear the *click* of the compressor clutch. Go back to your gauges, open the low side, (high side CLOSED) and you should see the low side drop as the high side builds - success.
3. The British Port: I'm embarrassed to tell you that I literally spent MONTHS trying to figure out why the low side pressure would not drop once the clutch was activated and I was trying to fill my system with R134, only to find that the Evora port is either longer, or the Schraeder valve is deeper, but I had to push in on the coupling to open the port and allow refrigerant into the system. If you have a set of gauges with non-screw down couplings (like me) and you can't seem to get the compressor to take refrigerant (low side gauge stays at can pressure around 80psi), try that simple trick before you go out and buy a new compressor.
Hope this helps a few Evora owners keep their cars out of the shop. I'm not a professional mechanic, so please comment or contribute if there is more to add!