Update on the 2005 Yukon HVAC system:
The AC compressor, tensioner, small belt I installed last August (and deslugger) all seem to be working fine.
Last year in my limited driving on that I had noticed that the AC changed by itself to heat on driver side, and there was clicking under middle of dash. One could stop and turn engine off and that would re-set. Apparently this is due to a faulty door/flap actuator under the dash, and is a common problem on Yukons, Suburbans, GM trucks. So I took off the underside cover, of course being GM the innermost bolt was like impossible to get to, dug out a 7mm deep socket and was finally able to get that (read posts about folks having issues with that, and just leaving that screw or cover off). Anyway, that actuator has 3 positions, and I got it into the AC mode and then unplugged the harness so we'd have AC. But it turns out that this meant no heat.
Santa brought Mrs. Cusser a new aftermarket Dorman actuator ($50, why buy more-expensive GM again when there is a trail of bad ones posted on Internet?), and I braved our 45F wind-chill yesterday to install it, actuator is held in by 2 hex head screws. Well, once again, cannot access one of the screws due to the center hump being in the way, what terrible engineering. The screws take a 5.5mm or 7/32 inch socket, and I had to grind down BOTH ends of the socket to shorten it (recessed, so no access to use an open end or box wrench, had to use the ground-down socket and a 1/4 inch ratchet wrench; no room to fit in a thumbwheel-type 1/4 inch ratchet either
Anyway, (using online instructions) I set the flap to align with the position of the new actuator, and bolted that in, reconnected the harness to the actuator, reconnected the battery, waited a few minutes, turned the ignition switch to on for a few minutes so computer could learn stuff, then switched ignition off for 10 seconds. So now we have both heat and cooling. I left the lower cover off, don't see any real reason to reinstall that.
Thanks again, GM !!!! What a poor design. I know a shop gets $300-$400 for replacement of these, had it done at a shop on the 1994 Suburban, and remember the mechanic saying how much of a pain it was !!!