Blower Motor Resistor
Does Your Heater Fan Only Work on High?
Maybe this is not exactly regular maintenance, but this is a common problem with TJ Wranglers. You may find one day that the fan for your heater and AC, if you have factory AC, stops blowing or only blows on high or has other fan speed problems. Usually, this is caused by a bad blower motor resistor.
There is a blower motor under the dash by the passenger's feet. The blower motor resistor is plugged in to the HVAC box right next to the blower motor. You have to unscrew the plastic cover plate to expose the resistor. The resister pack is also held in place by a couple of small screws.