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Servicing should only be performed by a Qualied Service Agent
VARIABLE FREQUENCY DRIVE – BLOWER SPEED AND PRESSURE READINGS
The instructions for the VFD are sent from the CCB to in the form of a DC current. The chart below lists the
current readings, the frequency signal displayed by the VFD, and the pressure switch settings needed for
the CCB to let the burner operate. The frequency numbers displayed may vary slightly with slight variations
in the DC voltage generated by the CCB. If the water heater exhibits poor run characteristics check the
frequency display. If the frequency is more than 5% out of range, check the DC volt signal at the terminals
shown on page 43.
Voltage – Frequency – Speed Instructions – VFD
Model SUF 400 SUF 500
Instructions Volts DC
Terminals OV and AI1
0 - 10 VDC 0 - 10 VDC
Volts Frequency Pressure w.c. " Volts Frequency Pressure w.c. "
Purge Speed 7.77 150 Hz+/-2 5.85" 7.77 150 Hz+/-2 5.85"
Ignition speed 7.53 150 Hz+/-2 5.3" 9.10 181 Hz 7.2"
High speed 7.77 150 Hz+/-2 5.85" 9.84 196 Hz 9.0"
VFD Part Number 197500-000
Frequency is displayed
in the red LED. 155 Hz