If you read my 2 posts above you will see that for '98 the relay does not really control all the blower speeds, at least not in the normal way. It switches the NC & NO contacts from NC to the NO contact when on high which then bypasses the resistor & also gets its power from fuse 11 (40a) in the PDC. When on the lower 3 speeds the power comes from fuse 8 (20a) in the fuse block & through the NC contact. So it is possible that the relay is bad (or fuse 11). It should click when going from high to any lower speed (if the speed switch is good). When you hear it click it may be closing to the NO contact but that contact could be bad & no power would get through for high speed if that happens.
Go to the link below to see the FSM & in the heat & a/c section of the wiring chapter on page 4 you can see how it works.
See online read only FSMs here:
Jeep Information Center, Jeep Parts Catalog, Jeep Repair Manual & More
You may have to go to the bottom of the page & pick Jeep Resources & online manuals if it directs you to home page rather than the knowledge base.
Pick your model & year then on the drop down menu pick the chapter you need.
In that diagram look at the blower motor relay. The #3 terminal is the NC one for speeds 1-3 & the #4 terminal in the NO for high speed (which closes under power from terminal #5). From there you can try jumping from terminal 1 (probably labeled 30) to terminal 4 (probably labeled 87) to see if that gives you high speed. If yes then the relay is bad.
Edit: Typing while WD was posting.