To change speeds, the energized speed had to be turned off, then it waited 5 minutes for the head pressure to subside, then it engaged the other speed winding.
I have an 11-year-old 2-stage Lennox heat pump (3 ton, 18.6 SEER) in a 1700 sq ft Florida ranch. The high stage sometimes kicks in for a few minutes according to some trigger that I haven't yet figured out; the A/C mostly runs the low stage when it runs at all. The unit never starts up in high stage, and there is no gap when transitioning between low and high stage. I'm assuming here that noticeably higher blower speed corresponds to high stage operation.
I've been satisfied with the heat pump for the 4 years I've owned it, and I'll be strongly biased toward getting another heat pump similar to it when it comes time for replacement (goes out of warranty next year).
BTW: the previous owner paid $9.5k (after Lennox rebates) to have this unit delivered and installed by a local reputable HVAC contractor. The time of year was April, so it wasn't an emergency install.
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