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| Service Manual | |
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1 Service (continued) |
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Sequence of operation |
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Table 1A Sequence of operation |
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OPERATION |
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1. Upon a call for heat, the control turns on the water heater pump. | WHR: Standby | |||
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| OUT: 123.8F(129) | ||
2. The control connects 120 VAC to the blower. The blower does not |
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run at this time. |
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• If the unit is equipped with a flow switch, it must close before the |
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control powers up the blower. |
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• The manual reset high limit must be closed before the control | WHR: Standby | |||
powers up the blower. | ||||
OUT: 123.8F(129) | ||||
• If the unit is equipped with a solenoid valve and/or a vent | ||||
valve, they will be energized along with the blower. |
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• If the unit is equipped with a gas pressure switch, it must close |
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at this time. |
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• If there is an auxiliary device connected to the unit, the unit |
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will then provide 24 VAC to its enable relay. If the auxiliary |
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device has a proving switch, it must close before the |
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sequence continues. |
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3. The control then starts a 10 second prepurge cycle. | WHR: PREPURGE | |||
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| OUT: 123.9F(129) | ||
4. Once the prepurge cycle is complete, and the blocked drain | WHR: IGNITION | |||
switch is closed, the control starts the 5 second trial for ignition by | ||||
sending spark voltage to the spark electrode and opening the gas | OUT: 123.9F(129) | |||
valve. | ||||
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5. If the control does not detect flame by the end of the trial for |
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ignition, the control performs a 10 second postpurge, another |
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prepurge and tries to light the burner again. | WHR: POSTPURGE, PREPURGE | |||
If the burner does not light after 4 trials on Models 150 - 399, the | ||||
control locks out for 1 hour and then tries another set of 4 trials. | OUT: 123.9F(129) | |||
If the burner does not light after 1 retry on Models 500 - 800 the |
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control will lock out. |
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6. If the control detects a flame before the trial for ignition ends, it | WHR: WHR 20% RATE | |||
begins to modulate the burner in order to maintain the set point. | ||||
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| OUT: 124.8F(129) | ||
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7. Once the call for heat is satisfied, the control will turn off the burner. | WHR: POSTPURGE | |||
The blower will remain on for the 10 second postpurge cycle. The | ||||
water heater pump will continue to run for its pump delay time, | OUT: 127.4F(129) | |||
then turn off. | ||||
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8. Water heater pump off. | WHR: Standby | |||
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| OUT: 124.7F(129) | ||
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