sometimes this is caused by the blower resistor heating up and shutting the circuit down, or it could be in the blower itself heating up and shutting down.
Motor hasseized.
One of the reasons a 2000 Jeep Cherokee heater would randomly blow cold air and then hot air and then cold might be that there is a problem with the hot/cold duct. The air or a vent might be inadvertently blowing periodically.
Blown fuse, defective blower motor, or defective blower motor resistor pack.
There might be a bad fuse causing the heater to not work. Check the fuses if they are all ok you may have a bad blower motor. when you turn the heater on and no air is blowing then it is your blower motor.
Heater blower motor is defective and locked up, or possible short in the wiring.
check for a blown fuse that says heater or blower motor
Soot blowing is done in air pre heater by a blower called swing blower which is different from half retractrable or full retractable or deslagger.
check the blower motor resistor
blower motor bad or no power to it chech fuses blower switch blower motor
Blown fuse, defective Blower Motor Resistor Pack, Defective Blower Motor, or Defective Blower Motor speed control switch.
Blower resistor is under the glove box. It is diamond shaped with 2 screws holding it in.
There is an electrical short to ground in the fan switch or in the blower motor itself.