With Trane heat pumps, when the fan switch is set to ON at the
thermostat, the fan (House Blower) normally runs at 50% air flow. If
the compressor comes on, the blower will speed up to 100% after a
delay, usually 1/2 to 8 1/2 minutes, depending on the program. The air
flow is set by dip switches on the control board. It should then be
verified by measuring with a flow hood.