wanted thermostat operation

• lacks fan circulate mode
• assumes single-stage heat
• wired to Y1 instead of Y2
• sets Aux Heat for > 1° setting increase

Assumptions

• ASPF426016EA furnace provides 24VAC for controls,
  to which it only responds.
  full (40A) heat by W2 and half by W1.
• GSZ130421AE heat pump sets W1 for defrost
• OT18-60A sets W2 for temps too low for GSZ130421AE
• Service Instructions

Sensi ST55

• 3-stage heat (Y2, W1, W2) and 1-stage cool (Y2 + O)
• should NOT set Aux (W1) heat for setting increases > 1
• sets W[12] only for too slow Y2 temperature increase rates
• If/when OT18-60A sets W2,
  ST55 drops Y2 (and W[12]) when indoor temp > setting.