sounds like the evaporator his cooled its last cool. Probably a hole in the inlet or outlet tube, or in the core somewhere. If it were me, I was planning on keeping the car for any extended amount of time and valued A/C the way I do I'd pick up a new one at your local parts store, if not the dealer ( $$
I've never tackled an evaporator on a GVR-4 (though I've been through about every other
A/C component), but I did have to pull out the lower ducting, evaporator and box on my 1G to get at the wiring harness. Let me tell ya, I'd rather not go through that debacle again! Not fun and I sure don't envy you right now. Though, I do loves me some cold A/C...
Some pages from the FSM that may help you out: