CIRCUIT OPERATION
When the thermostat contact closes, a circuit is completed through the closed high temperature switch, low water switch, and coil of the time delay relay. Since the timer is an off delay timer, TDR contacts close immediately and energize the blower motor relay, Figure 9–19. This causes the BMR
contacts to close and connect the blower motor to the power line.
The air flow produced by the blower motor causes the flow switch to close and energize the coil of the high pressure pump motor relay, Figure 9–20. This causes the HPM contacts to close and connect the high pressure pump to the line. The circuit is now in full operation. The circuit will continue to operate in this manner until the thermostat contacts reopen, Figure 9–21. When the thermostat contacts reopen, power is disconnected from the high pressure pump motor relay and the time delay relay. Because the
time delay relay is an off delay timer, it does not start timing until the coil is deenergized. The TDR contacts will remain closed for a period of 1 minute before reopening. This permits the blower motor to remove any smoke and fumes from the combustion chamber. When the TDR contacts open, the circuit is back in its original state as shown in Figure 9–18. If the high temperature switch or low water switch should open, it would have the same effect as opening the thermostat.
