Some of the reasons a Jeep heater is not working are attributed to functionality failure, including electrical failure, a clogged heater core and a low level of the coolant in the radiator. The heater is a complementary component of the radiator in a Jeep.
The hot coolant from the radiator is supplied to the heat exchanger connected to the heater core, which heats the air. A low coolant level means less heat is supplied to the heat exchanger, which affects the heater's functionality. Problems with the electrical system include a blown fuse, destroyed heater switch or an open thermostat. These conditions affect the circulation of the coolant.