Following is a procedure that has worked for many Jeep GC's.

I have removed the evaporator in my 94 Gr. Cherokee to replace a leaking
evaporator. Don't do this unless you have a masochistic streak. The drain
runs into the pax side longitudinal beam of the vehicles frame and drains to
the rear, according to the shop manual. You can't see anything obvious from
underside.

There is a TSB repair procedure developed by Jeep to service the drain from
inside the pax compartment w/o removing evaporator case. I have the
procedure on Alldata CDROM but apparently there is no way to download to a
file that I could send. Following is the procedure:
1) Pull the carpet on front pax side back to expose the circular duct at the
base of the firewall.
2) Drill a 1/4" hole in the center of the circular duct outlet. Water may
run out when you drill this opening.
3) Run a coathanger wire or similar through the drilled hole, and down the
tube to "rod" it out. Outlet is forward and slightly downward.
4) After clearing the drain, fashion a plug from some handy material. Parts
store has various size rubber plugs. Hot melt glue might work.

This will not work if the blockage is above the 1/4" hole opened in the
circular duct.
This would indicate lots of debris/dirt in your evaporator case, and
you'll have remove the case,... bad news. I spent 30-40 hours all told to
disconnect all wiring, remove dash assembly, remove evaporator case, replace
evaporator, replace dash, reattach all wiring. I "lost" one male wire
connector and searched forever before finding. It had fallen behind the
carpet. I hope the above fixes your problem. It's simple and easy.

good luck

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