Variable Frequency Drive - Blower Speed And Pressure Readings - A.O. Smith BTH 120 Series Service Handbook

VARIABLE FREQUENCY DRIVE – BLOWER SPEED AND PRESSURE READINGS
The instructions for the VFD are sent from the CCB 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
OV and AI1 shown on Page 42.
Voltage – Frequency – Speed Instructions – VFD
Model‑Series
BTH 400‑100
BTH 400‑104
BTH 500‑100
(Production thru
12/08
BTH 500‑100
(Production from
01/09 thru 02/11
BTH 500‑104
(Production from
03/11 to present)
VFD Part Number
Frequency is displayed
in the red LED. 155 Hz
Ignition (Low Speed)
Volts Frequency Pressure
0 - 10 Hz w.c. "
VDC
7.53 150 5.3"
5.48 109 7.2
9.10 181 8.0
9.10 181 8.0"
5.48 109 7.2"
Servicing should only be performed by a Qualified Service Technician
Purge (High Speed)
Volts Frequency Pressure
0 - 10 Hz w.c. "
VDC
7.77 155 5.85"
8.15 163 6.0"
9.84 196 9.0"
7.77 155 5.85"
7.92 158 6.0"
197500-000
Run
Volts Frequency Pressure
0 - 10 Hz w.c. "
VDC
7.77 155 5.3"
8.15 163 6.0"
9.84 196 9.0"
9.8 196 9.0"
10 200 9.0"
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