no hot air

i recently purchased a 89 gt the heater worked great but no a/c so i charged the a/c it works great but now no hot air?

I have a '93 stang that didn't get hot air and originally i thought it was a vacuum leak. then i realized that the plastic blend air switch (round, adjust air temp) was cracked and although it felt like it was rotating around to the red warm air selection it was actually just rotating around the little shaft. I got a new knob at the local salvage yard and problem solved.