Lochinvar COPPER-FIN 497 - 2067 - Manual (Page 61)

8
Maintenance
(continued)
9. 24VAC is supplied to the intermittent alarm field safety
contacts, B1 and B2.
10. 24VAC is supplied to the water flow switch.
11. 24VAC is supplied to the TH terminals on the ignition
module.
12. As power is applied to the TH terminals on the ignition
module, 120VAC is switched from the F2 terminal to start
the combustion air fan at full speed on Models 497 - 747
and at low speed on Models 987 - 2067.
13. 24VAC is supplied to the C terminal of the air pressure
switch. As the low air switch makes, power is supplied to
the ignition module.
14. 24VAC is then supplied to the PS terminals on the ignition
module as the air pressure switch makes to prove fan
operation.
15. The combustion air fan operates for the pre-purge period.
16. At the end of the pre-purge, 120VAC is applied to the hot
surface igniter and the trial for ignition light.
17. The hot surface igniter proves 1800°F (982°C) ignition
temperature by current draw through the ignition module.
18. The ignition module supplies voltage to the MV terminals
on to the gas valve(s).
19. The first stage gas valve(s) opens and supplies gas to the
orifice and burner inlet to pre-mix.
20. The gas/air mixture is forced into the burner and out of the
burner ports under pressure.
21. The hot surface igniter lights the gas/air mixture and
then serves as a flame sensor to prove main burner flame by
rectification.
22. Burners are now firing for approximately 50% of the
heater’s
input.
23. 24VAC is supplied from the second stage of the electronic
temperature control across the 2C and 2NO terminals on
the terminal strip on to a control to a relay.
24. The control relay switches the fan on Models 987 -
2067 to high speed and energizes the gas valves for the
remaining 50% of burner input.
25. The remaining gas valves open and supply gas to the
orifice inlet to pre-mix.
26. The gas/air mixture is forced out of the burner ports
and light by carryover from the burners currently
firing.
27. The heater is now firing at full rated input.
Installation & Service Manual
Heat transfer process
28. Heated products of combustion pass over the heat
exchanger transferring heat to the water.
29. The rate of flue product movement is controlled
by “V” baffles on the heat exchanger to maximize heat
transfer.
30. Flue products pass into the flue collector and are
exhausted from the unit.
End of sequence
31. Set point for the high fire on the electronic temperature
control is satisfied.
32. Power to all valves is turned OFF on F9 systems and
power to the high fire gas valves is turned OFF on M9
systems.
33. The water temperature continues to rise and the set
point for low fire is satisfied (M9).
34. Power to the low fire gas valves is turned OFF (M9).
35. The combustion air fan runs for a 30 second post
purge timing and turns OFF.
36. The appliance is now in a Standby Mode waiting for
the next “call for heat”.
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