No heat

I have a 1990 Beretta GT that I recently switched the interior in. The whole dash was replaced, but the wires from the previous dash stayed in. Now its all put back together but the only thing that doesnt work is the heater. There is no warm/hot air blowing, even after the engine has heated up for a long time.

Does the fan work, but it just blows cold air? If so, maybe the linkage that runs from the dash controll to the thermostat was damaged during the interior swap.

My first guess would be the heater core, but also it could be the damper / director doors could be stuck, or popped off or something to that extent.

To check those doors, I'm not exactly sure where it is in your car, but you'll need to look most likely somwhere back behind the glovebox near the firewall where the heater core lines come through the firewall. The director/damper doors should be inline with those lines. Make sure one isn't stuck or anything.