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Service Reference Manual SEQUENCE OF OPERATIONS
2-7
SRM-HW/HWC 2/99
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-W circuit is interrupted.
11. When the heat call is satisfied, the thermostat will
interrupt the R-W circuit. 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-W circuit is
closed). When the R-W circuit 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.
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-W circuit 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-W circuit 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).