IBC AHU Series - Page 44

Required if boiler does not have an integral pump.
Dry contact from air handler to boiler / enables call for heat.
Reversing valve (O or B) is selectable via the blower control interface
W1 = heat pump, W2 = energize TT for boiler - removes heat pump
Not used
Figure 44 Single-stage heat pump with boiler backup, primary/secondary piping (2-stage thermostat)
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Section: Installation