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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 38.
Voltage – Frequency – Speed Instructions - VFD
Model
Instruction Volts DC
Terminals 0V and AI1
Ignition (low speed)
Purge (high speed)
VFD Part Number
Frequency is displayed
in the red LED. 155Hz
A.O. Smith – Technical Training Department
CYCLONE Xi COMMERCIAL GAS WATER HEATER
BTH 120 thru 500 SERVICE HANDBOOK
BTH
400
0 – 10
VDC
Volts
Frequency
7.53
150 Hz+/-2
7.77
155 Hz+/-2
155
Servicing should only be performed by a Qualified Service Agent
BTH
500
Pressure
w.c."
5.3"
5.85"
197500-000
39
0 – 10
VDC
Volts
Frequency
Pressure
9.10
181Hz
9.84
196Hz
Ashland City, Tennessee © 2009
w.c."
7.2"
9.0"
316586-000
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