What causes a 1991 Acura Legend heater to not blow hot air if there's no leakage on the heater core or smell of coolant?
thermostst is stuck
If your heater core is LEAKING engine coolant so that your engine coolant level drops too low or the engine coolant is lost completely and causes your engine to overheat then your engine can be damaged beside the mess the leaking coolant makes inside your vehicle ( you might be able to just temporarily bypass the heater core so that no engine coolant is flowing through the heater core )
Possible causes; Low coolant, broken water pump, severely clogged cooling system. The heater uses the heat in the engine coolant circulating through the engine. It uses a heater core which is basically a smaller version of the car radiator. If there is no coolant flowing, the heater core will not be able to warm incoming air.