would low refrigerant in my A/C keep my car from having heat? on 1990 Cadillac DeVille

I have a 1990 De ville and the a/c unit needs to be recharged.The system runs but no hot air comes from the vents. I have no leaks. last year the heat worked fine with the exception that it wasn't very hot. Now I have no heat only cold air. Fuse(s) are good and I don't have a clue as to what's the matter, could someone assist me in getting heat?

Asked by for the 1990 Cadillac DeVille
just to add, programmer motors were a big issue with the old caddys. get a shop to check it for you to verify.

thanks Roy, i will take it to the shop and let them test the programmer. I will post the findings as soon as I get it done.
1 more answer , 1 more comment
a/c low charge has nothing to do with your heat. check your coolant levels. also monitor your vehicles operating tempature. if it never gets to normal operating tempature you might have thermostat issues.
Thanks d11b I will have a look at the thermostat and go from their and I will post and let you know.