Feel the heater hoses at the bulkhead when the engine is hot. Both hoses should be hot. With the engine running, move the temperature control lever/**** completely both directions. You should hear the blend doors in the airbox moving. If not, check the connections, wiring, and vacuum lines. Make sure the vacuum lines are drawing a vacuum. If so equipped, make sure the heater control valve just inside the engine compartment is operating properly when the temperature control is moved. Make sure the cooling system is full and the thermostat is operating properly (look in the radiator with the engine one and at temperature-this will also tell you if the water pump is working properly).