On my 02 ranger the a/c is blowing hot. I took it to a friend who has a vacuum and recharging machine I pulled a vacuum on it and did a leak test, it passed with flying colors. He put gauges on it and put some refrigerant in and it started blowing cooler air but not really cold because he only had one can. So I was leaving today to go get some refrigerant at the store, got in my truck and its blowing heat.....again. I hooked the small gauge that came with my last cans and its in the red like its over pressurized. What is going on? It was perfect yesterday.

 

There may have been another issue if your AC suddenly start blowing warmer, if it was a gradual warming over quite a few months that would mean time to recharge, sudden change usually means a part issue.

Good read here: AGCO Automotive Repair Service - Baton Rouge, LA - Detailed Auto Topics - Automotive Air Conditioner Problems, Part II