Just curious be fore I go ripping out my cluster and dash is there any tests or thing to look for as to why my heater does not work? At them moment it does not leak or anything, just doesnt blow hot. Incase it is needed, the car is a 86 GT, manual windows and locks, AOD, with AC.
The first thing I would do is make sure that the door to the blower motor is opening to pull in air from inside the car. I'm not real familiar with the pre-87 models, but you should be able to see it under the passenger side dash.