Package heat pump.
Product 542BU0030000PBAE (actually, first 0 is a greek phi, I think.)
I'm guessing it is a 1977, 35+ years old.
It had an old mercury bulb tstat on it and new tenants simply
wanted something modern and nice.
They wanted me to install a Honeywell they bought.
I did. Heating and cooling were fine.
However, when I turned the thing to OFF, the contactor
for the compressor & outdoor fan stayed on.
I tried a good Honeywell off my van. Same behavior.
Called Honeywell. They thought my contactor was merely stuck.
It wasn't. I didn't spend much time on it before it started raining on
me, but it appears the W terminal on the unit was energized. Y wasn't.
And that seemed to energize the the contactor, judging from its removal
de-energizing the contactor.
I don't remember seeing an O or B on the unit's terminal strip, so I'm
thinking W was the correct place for the reversing valve wire.
Of course, I don't have the wiring diagram. In hindsight, I should have
taken the wiring diagram to the dry and perused it there. But the rain
was gaining energy!
So if anybody has a wiring diagram or can help, I would be extremely