2006 Ford Five Hundred
The fan always blows.
Sometimes it blows cold, other times not. No rhyme or reason. Driving or idling doesn’t affect how it blows or cools. Problem is getting it diagnosed. I’ve had it charged and checked for leaks. What would be a reasonable price the compressor replaced?
Odds are the compressor is fine. The problem is likely in the controls. Where that problem lies I cannot tell you. If I had a schematic I could possibly point to a few trouble areas but my info is lacking that particular model.
I do not know if your model has a VLCM (variable load control module) or Constant Control Relay Module. The VLCM or CCRM engages the compressor with input from the PCM (Powertrain Control Module) which gets its input from various pressure switches, sun sensors, and so on.
Someone needs to go over the factory wiring schematic (Helm publication for instance) and get a rough feel for how this is wired up. Things used to be simple in the A/C wiring world. Not so much anymore.
might be as simple as a dying A/C clutch. If it is, it’s cheap and easy to repair.
Is this a manual or automatic AC system?
Tester
If the passenger compartment heater/cooling fan is blowing all the time, always at the same speed I presume, even when the AC is turned off, then start by testing and probing the AC control system. One test the OP could do is determine how the temperature control affects the temperature of the air coming out. And the OP could try to determine if the fan is blowing at the highest speed, or the lowest speed, or somewhere in between.
The next step would be to have it diagnosed for the problem!
Since it sometimes blows cold, it would seem the compressor is probably working and the system has retained refrigerant, however a visit to a qualified AC technician is the way to find out.