ULTRAFORCE COMMERCIAL GAS WATER HEATER
SUF 120 thru 400 SERVICE HANDBOOK
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 33.
Voltage – Frequency – Speed Instructions - VFD
Model | SUF |
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| 400 |
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Instruction Volts DC | 0 – 10 |
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Terminals 0V and AI1 | VDC |
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| Frequency | Pressure |
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| W.C.” |
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Ignition (low speed) | 7.53 |
| 150 Hz+/- 2 | 5.3” |
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Purge (high speed) | 7.77 |
| 155 Hz+/- 2 | 5.85” |
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VFD Part Number |
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155
Frequency is displayed in the red LED. 155Hz 
State Water Heaters – Technical Training Department 34 | Ashland City, Tennessee © 2009 |
Servicing should only be performed by a Qualified Service Agent |