A/C condenser was new when I bought the truck, approaching a year ago. I purchased the truck during warm weather and the A/C ran fine all summer. But now when I check the pressure, my gauge doesn't move. I am putting it on the Low pressure valve, and have put the rest from a partial can I had left over from my previous vehicle. I use the truck for hard work, and in Ohio, I experience both extremes when it comes to temperature and is always fluctuating. I just had my mechanics fix the heat not working and a leaking heater core, along with waterpump, which was also leaking. Is it possible they might have damaged a line in the A/C system? I keep getting a low reading on my valve for the freon. Maybe worth just buying a new can to test if things change? Could've been possible previous owner hadn't filled it in a while, and the amount I used my A/C last summer, along with the fluctuating temperatures over this winter, and the troubleshooting from changing fan/ ac settings while trying to get the heat working may have used the rest? Like I said I have receipt from the work previous owner had done on the A/C condenser, and it seemed to be working just fine before winter/before I had recent work done, just hard to tell if it was working when it was freezing cold outside, and recently it's been back in the 70s.

 

What year is the Ranger and what is the engine size?

The compressor will not come on if pressure is too low or too high
You don't mention if compressor is coming on?

AC is used all year long, when you select Defrost compressor will come on to Dry the Air in the cab.
So not a matter of disuse

Not likely that heater core or water pump repair would effect the AC system, but...........anything is possible.

Depending on the year of the Ranger you will have a cable or electric Blend Door
Blend Door is operated by the Temp ****/slider in the dash, it controls air flow thru heater core
HOT sends all air thru heater core
COLD blocks all air flow thru heater core

Heater core is always hot, always has coolant flowing thru it, so if Blend Door is stuck in HOT position then no AC cooling even if compressor is working
Blend Door is a common failure in Ford Trucks, especially the electric models, 1995 and up