Armstrong World Industries 302, 243, 242 Limit/Rollout Opens, Pressure Switch Opens Blocked Flue

SRM-HW/HWC 2/99

Service Reference Manual

9.After 30-second “on” delay, the circulating air blower relay energizes the heat terminal and the circulating air blower is energized.

10.The unit will continue to operate normally until the R-Wcircuit is interrupted.

11.When the heat call is satisfied, the thermostat will interrupt the R-Wcircuit. This causes the 24-volt signal to the white wire in the unit to be de-ener- gized.

12.The gas valve closes immediately as 24V through pin 4 of the 6-pin ignition wire harness is de- energized by the ignition control.

13.The ignition control initiates a 120-second circu- lating air blower “off” delay and 5-second com- bustion blower post-purge delay.

14.After 5 seconds, the combustion blower shuts off.

15.After 120 seconds, the circulating air blower shuts off and the system returns to standby mode.

Note: During a call for heat, the green LED shows consistent fast flash (as long as the R-Wcircuit is closed). When the R-Wcircuit is interrupted (indicating the heat call has been satisfied), the green LED returns to a consistent slow flash.

LIMIT/ROLLOUT OPENS

In all modes of operation, 24VAC is supplied to the ignition control 24VAC hot terminal and is passed through the ignition control to pin 6 of the 6-pin ignition wire harness.

1.A 24-volt signal is sent from pin 6 of the 6-pin ignition wire harness to one side of the Normally Closed manual reset rollout switch, across the rollout switch to one side of the Normally Closed auto reset limit switch and across the limit switch to pin 1 of the 6-pin ignition wire harness.

2.This circuit energizes whenever line voltage power is supplied to the unit.

3.If the circuit is interrupted by either switch opening, the 24-volt signal to pin 1 of the 6-pin ignition wire harness de-energizes.

4.This causes the combustion blower relay to energize, sending L1 power to the CMB BLWR terminal on the ignition control. It also causes the circulating air blower heat speed relay to ener- gize, sending L1 power to the ACB HEAT terminal on the ignition control. This causes both blowers to start immediately.

5.The ignition control lockouts the spark ignition cable terminal and pin 4 of the 6-pin ignition wire harness until the 24-volt signal is restored at pin 1 of the 6-pin ignition wire harness.

6.The circulating air blower and the combustion blower are energized until the 24-volt signal is restored at pin 1 of the 6-pin ignition wire harness.

SEQUENCE OF OPERATIONS

2-7

7.The green ignition control LED shows a 4 flash fault code (indicating limit switch/rollout switch open).

8.When the 24-volt signal is restored at pin 1 of the 6- pin ignition wire harness, the ignition control starts a 5-second combustion blower post-purge delay and a 120-second circulating air blower “off” delay.

9.Once the delays have timed out, both blowers stop and the green LED flashes a consistent slow flash if no heat call is present. (A consistent fast flash appears if there is a call for heat.)

Note: The limit switch resets automatically when temperatures are acceptable, but the rollout switch must be manually reset by pushing in on the small button on top of the switch.

The reason why the switches opened must be determined before any corrective action is taken.

PRESSURE SWITCH OPENS (BLOCKED FLUE)

When the R-Wcircuit is energized, a 24-volt signal is sent to the ignition control. This starts the call for heat.

1.The 24-volt signal from the R-Wcircuit energizes the combustion blower relay, sending L1 power to the CMB BLWR terminal on the ignition control. This starts the ignition control.

2.At the same time the combustion blower relay energizes, the 24-volt signal is sent to pin 2 of the 6- pin ignition wire harness and from pin 2 to one side of the Normally Open pressure switch.

3.When the combustion blower causes the pres- sure switch to close, a 24-volt signal is sent across the switch to pin 5 of the 6-pin ignition wire harness. The 24-volt signal energizes at pin 5 and the ignition sequence continues.

4.If the combustion blower fails to close the pres- sure switch, the 24-volt signal is not sent to pin 5 of the 6-pin ignition wire harness and the ignition control does not initiate a 30-second pre-purge delay.

5.No signal is sent to the spark ignition cable terminal on the ignition control or to the gas valve through pin 4 of the 6-pin ignition wire harness.

6.The combustion blower continues to run for 60 seconds. After 60 seconds, the ignition control automatically de-energizes the combustion blower relay. This interrupts L1 power to the CMB BLWR terminal on the ignition control.

7.The combustion blower remains de-energized for approximately six minutes. During this 6-minute lockout, the green LED flashes three times (indicat- ing pressure switch fault—open or closed).