[Schurkey]

Heater core won't be any fun.

The one in mine ('88 K1500 regular cab) is aluminum; you won't fix it with solder. MAYBE some '88's got copper/brass cores, but I doubt it.

WHILE YOU'RE IN THERE, check on the foam gaskets that seal the joints of the heater box assembly. My foam was totally rotted--looked like foam until I touched it, whereupon it disintegrated into goo. My truck was always cold in the winter, warm in the summer--the gasket that seals the recirculation box to the firewall was practically gone, and created an enormous non-heated, non air-conditioned air leak.

I had to pull the whole dash down to fix the rotted gaskets. If I can find photos, I'll post 'em. I think they're on my other computer. Steering column comes OUT, entire dash tilts down about 45 degrees on a pivot. Basically lays on top of the seat. Kinda cool to see it that way...but there's still crappy access.

WHILE YOU'RE IN THERE, pull out the blower motor, and see if you can dig out all the pine needles, leaves, and other crap plugging the front of the A/C evaporator. I spent an hour or more blowing compressed air from the front, sides, and rear; dislodged a ton of crap. Between the compressed air and a shop vac, I got it pretty clean. Much better air flow through the ducts.



[Robot Voice]DANGER, WILL ROBINSON![/Robot Voice]
The 1988 GM official service manual DOES NOT provide the proper procedure for removing the far-right section of the blower/recirculation box. The box WILL NOT come out using that procedure. The correct--and much more involved 'n' difficult 'n' expensive--procedure is in the service manual SUPPLEMENT published later AFTER they figured out what they screwed up in the main service manual. I hope you don't need to remove that far-right box to replace the heater core. (I had to take it out to replace the rotted foam gasket)