1991 Chevy Corsica no heat

Hi:
It sounds like there is a problem with the heater core. There are two hoses that run to the firewall under the hood. One is an inlet, the other is an outlet. With the car running (at operating temp and with the heater on), carefully feel both hoses. Both should be very hot. (be careful not to get burned. The coolant going through them could exceed 200 degrees.) If one is hot and the other isn't, there must be something plugged in the heater core and it will most likely need replaced.

I hope this helps.

Joe