Variable Frequency Drive - Suf 119300 Thru 119500 - State Water Heaters 60120-100250 Service Handbook

VARIABLE FREQUENCY DRIVE – SUF 119300 THRU 119500
The SUF 119300 - 119500 models have a variable frequency drive (VFD) that controls the rpm of the
blower motor. The VFD receives a signal from the central control board that instructs the VFD to transmit
the proper frequency to the blower to produce the proper blower speed and proper input.
Three conditions must be met for the frequency drive to start the blower:
1. 120VAC must be supplied to the VFD 120VAC input.
2. The ignition control board closes an enable circuit – terminals LI1 and +24V
3. The ignition control board sends a 1-10VDC instruction – terminals 0V and AI1.
VFD (Variable Frequency Drive)
Servicing should only be performed by a Qualified Service Technician
VFD Display
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