Well, my .02. I don't have A/C, but after seeing what is involved, I'd say you have to purge it. My heater box splits top and bottom halves. No way to do that in the truck.
When I pulled mine, I unbolted the bottom of the dash, where it bolts to the right side wall, and the 2 screws to the left of the glovebox, then pulled the bottom out enough to get the heater box out.
Trust me, it wasn't as easy as it sounds.
The dash is a cast iron bitch to get out without pulling the windshield. There are screws under the rubber. They are barely accessible. If at all.
And here's a FYI for anybody whose heater controls work hard, check the shafts in the box. Turns out my cables were good, the shafts were rusty, causing them to bind and turn hard. A few minutes with a wire wheel, a couple dabs of grease, and it works nice and smooth now.
