Armstrong World Industries 242, 243, 302, 122 POWER Line Voltage, Second black wire, Low Voltage

SPECIFICATIONS Magic-Pak: HW/HWC

2-24

Detailed Sequence - HW

(w/Fenwal Triton 2461D Ignition Control)

Refer to Figure 2-4

POWER

Line Voltage

When the service disconnect switch is closed, power is sent to the unit (unit in standby, no signal from thermo- stat). Power (208 - 230 volts A/C) is supplied to the two black wires located in the junction block on top of the unit.

Line voltage will be present at the following locations:

First black wire

1.L-1 on the ignition control

2.Terminal on the transformer marked 208V or 240V (whichever is being used)

3.Common terminal on the blower capacitor

Second black wire

1.Supplies power to the one side of the induced draft blower

2.Common terminal on the transformer

3.L terminal on the blower control board

Low Voltage (24 VAC)

With the unit at rest (no call from the thermostat), 24 volts A/C will be found at the following points:

1.Red wire exiting the top of the unit

2.Terminal marked NO on the limit switch

2.Terminal marked 24VAC on the ignition control

3.Terminal R on the blower control board

CALL FOR HEAT

Line Voltage

The thermostat closes the circuit between R and W.

The following is the sequence of operation for the line voltage side of the unit:

1.Terminal TH on the ignition control energizes, causing a relay in the ignition control to close. This sends line voltage to terminal IND on the ignition control, causing the induced draft blower to start.

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 ener-

gizes, 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 ener- gized.

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/HWC

2/99