1992 Ford Escort temperature guage reads normal, but car on

It could be a few different things. Your dash controls have cables that go to your heater box to change from hot to cold, check to make sure they are not broken and they are operating properly.

Some vehicles have a shut off valve under the hood inline with the heater hose, some are vacuum controlled and some cable controlled. If its vacuum the car will have to be running. With a 2nd person in the car, have them move the heat/cold control slowly back and forth while watching the valve under the hood. It has a lever that should move when you do that.

It could be a clogged heater core. Remove both heater hoses, note witch 1 goes were. Using the garden hose push it against 1 of the tubes that go into the heater core and wrap it tightley with a rag, turn on water and check for flow, if not try it on the other tube.

Good luck