RC RA 0V AI1 +5V DO LI1 LI2 LI3 LI4 +15V
CYCLONE Xi COMMERCIAL GAS WATER HEATER
BTH 120 thru 500 SERVICE HANDBOOK
A.O. Smith – Technical Training Department 38 Ashl
and City, Tennessee © 2009
Servicing should only be performed by a Qualified Service Agent 316586-000
VARIABLE FREQUENCY DRIVE – BTH 400 and 500
VARIABLE FREQUENCY DRIVE
1-10 VDC Speed Instruction Enable Disable Circuit
The Cyclone Xi BTH 400 and 500 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 +15V
3. The ignition control board sends a 1-10VDC instruction – terminals 0V and AI1. See table
on the next page for voltage and frequency information.
GROUND HOT NEUTRAL
R/L1 N
G
BLOWER MOTOR WIRES
BLACK WHITE RED
U/T1 V/T2 W/T3
NOTE: BE SURE TO MATCH WIRE
COLORS WHEN CONNECTING BLOWER
WIRES OR BLOWER MAY RUN
BACKWARD AND CAUSE A FAULT.
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