I've seen a guy do dual 10" fans have good results. I don't know why one would go smaller on a single fan, I don't think the price differences are that much to justify it. Towing back and forth to HPO last weekend my a/c seemed to go a little warm on the highway while I was towing and then at some points my wife got a few splashes of cold water on her feet in the passenger seat. It didn't get warm, just warmer, still blew cold. Those splashes typically mean clogged drain line but the a/c was POURING water out the bottom like it normally would so I need to check into it. But if there is water collecting / freezing at the evaporator core it could cause the a/c to be warmer than it would normally be. It would also explain why it takes a while to go warm since the water would take time to collect. So it appears my a/c saga continues. But the issue of having no a/c at all right after startup is still a thing of the past.
BTW, one other thing I've learned about the a/c on these trucks is that is was a transition period from R12 to R134a. After the transition they discovered that evaporator cores that used the old fin spacing tended to grow mold and cause a musky scent in the cab when they were used with the new freon. There was a TSB about it that contained an updated part number for the evap core. The new version has more space between the fins and does not grow mold as a result. So if you get the musky odor that's what's going on.
