OK, so now I'm getting into this fix. Problem was more widespread than just the factory OEM part that was cracked.
Closer inspection of the broken drain trap showed that it cracked from the bottom up. This tells me that there was excess upward pressure on the assembly.
I had to cut away the old drain trap assembly to get it off. Once I did that, I noted that the Schedule 40 PVC pipe was effectively dangling. In fact, it fell apart as I shifted it just a bit. It broke away from the condensate drain outlet on the upper unit (circled in red), and I also found that it was not attached at the floor level, either. There's no evidence, at all, of any PVC cement at that joint (also circled in red.)
If you look closely, you can see the bend at the coupling on the vertical PVC pipe. Instead of cutting the pipe to the correct length, I think this is indicative of how Hanz and Franz just jammed this together, eventually leading to the failure at the joints. This discovery led me to trip number two back into town to Menards to get more PVC fittings. It would have been nice to have a small stock of the necessary fittings, but I don't keep a lot of 3/4" PVC fittings because I don't have much of it installed.
I'll install a new PVC condensate drain from the heat pump and the aux furnace (lower unit). I will also install union couplings that will allow me to easily clean this setup, should it ever be necessary.
