You may have a faulty expansion valve. It may prevent compressor from running long enough to cool your car.
Bad thermostat
Most likely a broken blend door. Check heatertreater.net for diagnostic information and an inexpensive fix.
possibly blown head gasket
Most common problem is that the blend door is stuck or broken.
blend door failure is a common problem on 97+ Jeep Cherokee
Can a 2004 Power Tech High Out Put Engine Fit in a 2001 jeep grand cherokee limited 4.7L v8
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.
The HeaterTreater is an after market kit that solves heater and AC for the Jeep Grand Cherokee and Laredo. It is much cheaper than the dealership fix and is easy to install. For diagnosis and info, check out www.heatertreater.net or search eBay for "heatertreater".
There is a dead short to ground in the circuit.
A short in the brake light circuit.
check pcv it maybe plugged
I would look for a Vacuum leak possibly under hood. Does your Cruise control work?