Well if it hasn't been charged in several years and was blowing cold when you got the car , I'd say Enrique was probably right. I would also schedule to have it charged, after he checks for a leak. True you don't drive it enough, but it needs the recharge to keep from getting worse. After recharging, just turn the A/C on for a bit of time when you start the car like you do periodically. Even in the winter.
I think you have owned the car almost two years now, not a stretch to need a recharge especially if you don't know when it was charged last.

Was that the problem you noted in your PM?

__________________
1986 Euro 500SEC "RUF" 9:1CR, "Rose"
1985 Euro 500SEC Cabriolet AMG Widebody
1982 Euro 500SEL "Blue"
2001 Texas Heeler (Aussie/Queensland X) "Sulphie",
2012 Queensland Red Heeler "Squeak"
Best dogs I've ever had.