sounds like a vacum leak in the temperature control panel or from the engine to the control panel, the line from the engine to the control panel is black, and gets split at the panel, has the engine been running a little rough or a lack of power, this might explain it
No
The fuse panel on a 1990 Ford Tempo is located under the dash to the left of the steering column.
A diagram for a ford tempo made in 1990 can be found online. It is a coupe model car.
You have a vacuum leak causing your vents to switch from dash to defrost.
1,3,4,2
1,3,4,2
replace the heater core
P185/75R14
Between the engine and the transmission.
You don't!
In many cases leaves can cause smoke to blow through the defrost of a 1990 Ford F 150
same motor, same driveline, same size, just electronics differ a little ( such as a/c or power locks etc..).