Assessments - 3, GPA: 3.7 ( )

Fabricante : Armstrong World Industries Arquivo Tamanho: 2.86 mb Arquivo Nome : Língua de Ensino:

2. When W is energized, a 24-volt signal is also sent to the W terminal on the blower control board. Approximately 60 seconds after W terminal energizes, the timer on the blower control board closes the heat speed relay on the board. This sends line voltage to the H terminal on the blower control board, which starts the circulating air blower. 3. The induced draft blower and the circulating air blower continue to operate as long as W is energized. 4. When W de-energizes, a relay in the ignition control opens. Terminal IND de-energizes and the induced draft blower shuts down. Approximately 90 seconds later, the circulating air blower also shuts down. Low Voltage The following is the sequence of operation for the low voltage side of the unit on a heat call: 1. A call for heat closes the circuit in the thermostat between R and W, sending a 24-volt signal to the white wire on the unit. 2. The white wire goes to the C terminal on the limit switch. 3. The 24-volt signal is sent from the C terminal (brown wire) on the limit switch to terminal TH on the ignition control. This causes the ignition control to close the line voltage relay, starting the induced draft blower. When the induced draft blower comes up to speed and creates enough negative pressure, the pressure switch closes. 4. With the pressure switch closed, the 24-volt signal goes to the rollout switch located over the burners. 5. The 24-volt signal from the rollout switch goes to the terminal marked P.SW on the ignition control, causing the ignition control to make a trial for ignition (sparking). Terminal V1 on the ignition control also energizes at this time, causing the gas valve to open. 6. At the same time that the C terminal on the limit switch energizes, a 24-volt signal is also sent to the W terminal on the blower control board. This starts the timer on the blower control board. Approximately 30 seconds after the main burners ignite, the blower control board closes a relay; this sends line voltage to the circulating air blower, starting the blower. 7. As long as W (white wire) is energized, the unit continues to operate. 8. When the heat call is satisfied, the circuit between R and W is interrupted. SRM-HW/ Service Reference Manual SEQUENCE OF OPERATIONS 9. When W de-energizes, the gas valve immediately Note: If the P.SW and TH terminals energize at the shuts down and the induced draft blower also same time, the ignition control will not respond. stops after several seconds. A pressure switch being stuck closed is an 10. The blower control board starts a countdown to example of what would cause this to happen. blower “off”. Approximately 90 seconds later, the circulating air blower shuts down. ROLLOUT SWITCH ACTIVATED LIMIT OPENS 1. If the conditions in the burner compartment cause the rollout switch to trip, the contacts on the switch If the limit switch opens for any reason during a call for open. This interrupts the 24-volt signal going to heat, the following happens: terminal P.SW on the ignition control, causing terminal V1 on the ignition control to de-energize. 1. If the limit switch senses that the temperature in This interrupts the 24-volt signal to the gas valve the unit is too high, the circuit between terminals C and immediately closes it. Since terminal TH on the and NC on the limit switch opens. This closes the ignition control and W on the blower control circuit between terminals C and NO on the limit board remain energized, the induced draft switch, interrupting the 24-volt signal to the pres-blower and the circulating air blower continue to sure switch and the rollout switch and causing run. terminal P.SW on the ignition control to de-2. The 24-volt signal to the ignition control can only energize. The gas valve immediately closes, as be restored if the rollout switch is manually reset. there is no longer a 24-volt signal at terminal V1 on 3. Once the cause of the rollout switch being tripped the ignition control. With 24 volts still going to the has been determined, the switch can be reset. blower control board and terminal TH on the 4. With the rollout switch reset, terminal P.SW on the ignition control, the circulating air blower and ignition control again energizes. The ignition induced draft blower continue to run. control makes a trial for ignition and operation 2. The circulating air blower and the induced draft returns to normal. blower continue to run as long as there is a call for heat from the thermostat or the limit switch remains open. 3. When the limit switch senses that the temperature in the unit is low enough, the circuit between C and NO opens and the circuit between C and NC closes. 4. With the limit switch closed, the unit again makes a trial for ignition and returns to normal operation. PRESSURE SWITCH OPENS (BLOCKED FLUE) 1. If blockage of the flue occurs, the negative pressure in the induced draft blower is reduced. At the set point of the pressure switch, the contacts open. This interrupts the 24-volt sign...

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