Technical information
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Servicing should only be performed by a Qualied Service Technician
VARIABLE FREQUENCY DRIVE – ALL MODELS
The BCL3 95T199 6NOX, (A)BCL3 85T275 6NOX and (A)BCL3 85T390 6NOX models have a variable
frequency drive (VFD) that controls the speed of the blower motor. The VFD receives a signal from the
thermostat and ignition control that instructs the VFD to transmit the proper frequency to the blower to
produce the proper blower speed and proper input rate.
Two conditions must be met for the variable frequency drive to start the blower at low speed:
1. 100 - 120VAC must be supplied to the VFD input.
2. The thermostat closes a contact through the low speed I/O module – VFD terminals LI1 and +24V.