the heater blower resistor is bad. located on firewall under heater hoses two 8mm bolts. about a twenty dollar motorcraft part. easy repair.
Typically a relay or resistor. But could be a blower switch or blower motor problem.
Check to see if the switch is any good . Most of the time it is the switch.
Could be a bad resistor pack at the blower motor Could be a bad low speed relay
there are resistors located by blower motor. could be open. they control blower speed.
Faulty Function selector switch. Consider replacement.
It has a bad "Blower Motor Resistor" The fan switch itself is fine.
it's a problem with the blower motor resistor
If the fan only blows on high in the Liberty, check the blower resister. The resister circuit is the most likely cause.
It could be a loose wire or a bad relay switch worse case the blower motor is going out
Replace the blower motor also.
If by quit working you mean quit blowing, the things to troubleshoot are the blower motor, the blower motor resistor switch, or the blower motor speed selector switch. If by quit working you mean it only blows cold or warm air, the thermostat is probably stuck in the open position.
sounds like you need to replace either the thermostat or the temp control switch