Most likely it is a resistor that has blown on the back of the controls.
Blower motor resistors are generally found nearby the blower motor.
blower fan not working
Have alternator checked. Should be getting 13-14 volts running. If not that, have battery tested.
Check for a vacuum leak either under hood or under dash Check the operation of the vacuum actuators under dash Check the operation of the selector switch Defrost is the default settting for this system
The Blower Motor Resistor Pack is defective. Replace it.
My '96 Cherokee Sport does, so I bet a '98 does.
Vacuum leak in one of the hoses I own a Jeep Cherokee Sport, found that a broken vacuum hose was the culprit. When there is a vacuum leak, the blower-ventilation defaults to blowing through the defrost vents. Once the vacuum lines are fixed, the other ventilation doors are able to function and open. Your set-up and placement of your lines may be different, but mine were located in the front-lower right of the engine compartment, running up the right side and ending in the back/firewall. The lines are cheap and easy to replace, took about 5 minutes and 3 dollars!
The grand Cherokee is a body style, sport is a trim package that is used on all jeep models(wrangler, Cherokee, grand Cherokee, patriot, ...)
The fuel pump is in the gas tank on a 1999 jeep Cherokee sport.
Yes, they are the same vehicle, the sport is just a option package.
1996-2000 Cherokee.
NoNo