Could be low on coolant or the heater core may be plugged or the thermostat is stuck open or the temp blend door is broken.
see the answer for how do you replace heater core 96 jetta its the same good luck and god speed
Disconnect the heater hose off the heater core on the firewall and remove the inside middle side panels along with the lower heater core panel and pull the core straight out.........
If you look from the engine compartment you will see the 2 heater hoses that connect to your heater core at the firewall towards the passenger side
Thermostat and/or heater core may be defective
Check the heater core, it is probably bad. It could be heater hose connections to the heater core, but I would bet on the heater core going bad.
The heater core can be found behind the passenger side kick plate. Remove the water supply hoses from your 1996 Chevy Impala heater core. Remove the heater core retaining bolts. Reverse the process to install the new heater core.
engine cover
the heater core was stopped up just flushed it out ok now
The dash must be completely removed in order to gain access to the heater box. Then the heater hoses are disconnected and the heater box is removed and opened up. That gains access to the heater core for relacement.
Easy to replace. Hard to get to.
Subaru leg out back 96 97