|No or Low Heat_____________________________________|
This can be difficult to resolve on these cars. Obviously, check the heater core for internal blockage. The hoses in and out of the core should be hot. It's not advised to eliminate the heater control valve.
There can be other problems- sensors, EATC, low coolant level, or air temperature door motors.
Related to this issue, as part of an old Technical Service Bulletin, Ford had the dealers move the location of the outlet air sensor. Originally, it was low on the right side of the air box. The new location is higher on one of the outlets. This is the heater box out of an 89 model.
The upper air valve/air temperature door sometimes leaks air, blending warm air with cool air. Not good on hot days.
Check that the door closes completely. There's a little slack for adjustment in the attaching screws.