i have a 1991 chevy that the heater or the ac does not work... we have put a freeon leak detector on the whole system and the only thing that showed any kind of a leak was the condensor... now i am considering doing a condenser swap with a another vehicle of mine and only the heater works on that truck... is the bad condenser going to affect the heater on the other truck??

no. the heater core is a whole different system from the a/c. pretty much the only thing that affects both of them are the cabin selector switch and the blower.