It could be the thermostat on the engine. If the engine does not warm up adequately the heater will never blow hot air.
windshield leaking heater core or heater core hoses.
yes it definitely will
the heater core
There are several things that can cause heater problems in your 1998 Jeep Grain Cherokee. The most common cause of heater problems is low fluid in your cooling system.
Leave it turned off.... doh
A squealing heater is more than likely a fan belt. It may be loose, or it may be worn and need replaced.
heat core. leak. thermostat. no antifreeze.
Heater Core for sure. Get this replaced and you will have no more problems.
Heater core
Did you check the thermostat? If so, try the heater core. check the air mix door in the heater it may be stuck and letting outside air in
the thermostat may be stuck open or the heater core may be plugged the thermostat may be stuck open or the heater core may be plugged
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".