Okay - With the 2005 schematic available -
First again I suggest reloading the previous tune and with KEY ON ENGINE OFF see if the AC compressor is cycling on/off. If you choose not to do that then read on or read on anyway.
With regard to your dual pressure switch - Fuse F14 in the smart junction box supplies voltage to that circuit. It is a 5A FUSE and is hot at Key On (run) engine off according to the prints. Check the fuse. If good and 12 vdc present keep going. With the engine running and the current program loaded (assuming you tried above and it proved nothing), Start the car and find the DARK BLUE WITH YELLOW WIRE (pin 1) that leaves the dual pressure switch connector and see if you have 12vdc on it. If you do, this part of the system is good. If not and the fuse was good and had 12 volts with key on you have three things to consider - 1. AC Clutch cycling pressure switch, 2. dual pressure switch is bad or 3. the system is flat out low on refrigerant.
Moving on if all the above checks are good -
The AC compressor system -
In the bussed electrical Center (I assume this is the box in the engine compartment - been years since I owned an 05-09) you can first check to see if Fuse F49 - 15A is good or not. This fuse will be hot at all times regardless of ignition key position. It provides the actual power to energize the clutch via the A/C Clutch relay. If good next would be to check the relay itself to see if it is bad. You could swap a relay of the same number from another non critical system to see if the A/C unit then works or you could actually pull it and check coil resistance properly with a Digital Volt Ohm Meter. Assuming the relay checks good we move on. The next thing to check would be Fuse F49 - 15A. This fuse provides the control voltage that fires the A/C clutch relay coil (which turns the compressor on) via the PCM. If that fuse is blown that will cause the system to not turn on. If that is good the next thing to check is to see if the PCM is actually providing signal for the A/C Clutch relay to energize. This is where it gets tricky if you aren't comprehensive of some basic electronic control theory.
The AC Clutch relay coil always have twelve volts present on both sides of the coil when not being commanded by the PCM to turn on. PCM controls this by a method called sinking. The PCM when told to turn the A/C clutch relay on will provide the ground (actually a logic low) which completes the path. That means when you check this circuit for the relay to be commanded on the Gray/White wire that goes to eh PCM from the A/C clutch relay in the "Bussed Electrical Center", will read less than 5vdc guessing and more likely closer to 1vdc. If the A/C clutch is being commanded off this wire's voltage will then read 12vdc or the same as the voltage on F49. Hope that makes sense.
Hope this helps you out. Check the fuses I mentioned first. THESE ARE IAW YOUR YEAR OF CAR'S ELECTRICAL PRINTS.
Bruce provided the link in this thread to me. So you can get to it. IT's a great resource.
Remember that the PCM has control of the AC strategy. IT is looking directly at the dual pressure switch circuit which ultimately allows the AC clutch to cycle on and off or to be locked out under low refrigerant conditions. As well the AC compressor as mentioned is bypassed when WOT is achieved or when defrost is selected (if they are still doing that at Ford). So it would be likely possible the tune was altered by the tuner. They should be more than willing to help you iron this out. I dare not ask who it is. I have a hunch. Good luck.
AND SORRY FOR USING THE 2011 PRINTS EARLIER.