My bro with a '00 Taurus 3.0L decided it was time to recharge the A/C. After lots of bs from every auto parts store in town and even the dimwitted advice of a local repair shop....
"Dear Jesus, that A/C system is on the fritz, please bring it by the shop so we can charge you out the ass for an INSPEKTSHUN"...
We found the appropriate valve, ran the car with A/C on full blast, and filled her up with 2 cans of the necessary refrigerant. And guess what:
Solenoid kicked on, and COLD AIR CAME THROUGH THE VENTS INSTANTLY. No questions asked, A/C now works on demand without fail through a whole day of his Jimmy Johns sandwich delivery madness.
Before: the A/C controls were completely unresponsive. Now they work perfectly. Who knew: on FORDS and GMS a redundant system disengages the A/C system when the refrigerant is low.
And guess what, I did the same exact thing with my '97 Grand Prix SE a day later and BEHOLD: solenoid kicked on, and COLD AIR CAME THROUGH THE VENTS.
A little disambiguation is necessary, as I had people telling me to run red dye through the system, or check the seals, or check the doo-hickey at the blah blah blah. All day long for 2 days...
Unnecessary.