The reason the A/C or the heat won't come out is probably the fact the fan is busted. My advice is to change the fan.
it wont blow heat itll blow cold air
It doesn't really blow it out it just warms the cold air.
check you antifreze level if it is low you wont have eat or if you get lots of fog your heater core is bad
Your heater will blow cold air only.
The front expansion valve is clogged.
you are low on coolingliquid !
THE CAUSE for this is that when your cold air is on the petrol is used to create air. and that is how cars create cold air
No, not if it's on a heat setting. Most home thermostats have a "Fan" setting that will blow cold air if the attic is cold.
heater core possibly plugged and leaking
No! Thermostat.
check heater fan to see if it is working.
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.