Assuming the blower fan is working but it blows cold air, it could be,Faulty temp blend door actuator.
Plugged up heater core.
Faulty thermostat,
Low coolant level,
Most likely it would be a blown fuse in the fuse block.
In many cases leaves can cause smoke to blow through the defrost of a 1990 Ford F 150
Yes it could also cause the A/C to stop working.
Coolant leak? Check your heater core.
Blocked heater core, faulty heater valve, disconnected connection to the heater valve.
A Ford Mustang does not have a heater coil. You must be thinking of your home HVAC.
could be the switch to turn it on or the heating unit itself, let an professional take a look at it
Only if the coolant is leaking from the heater core, but you will see this.
No , if you were to bypass the heater core , you would have no heat
Heater Core
In a 1996 Ford Aspire, the heater may not work due to several potential issues. A common cause is low coolant levels, which can prevent proper heating. Additionally, a malfunctioning thermostat, a clogged heater core, or a faulty heater control valve could also disrupt the heating system. Lastly, issues with the blower motor or electrical connections may prevent warm air from circulating effectively.
A block heater for that vehicle would be an option. If it came equipped with a block heater the cord would be found close to the battery.