W415-1007 / A
/ 07.18.12
14
4.7
SEQUENCE OF OPERATION - ECM X13 AND PSC
1.
Room temperature drops causing the room thermostat call for heat by connecting “W” to “R”. The control
verifi
es the limit switch is closed and both the pressure switches are open. The control energizes the
exhauster motor and waits for the pressure switches to close. The exhauster remains on and begins a 15
second pre-purge period. If the pressure switches do not close within 60 seconds, the control will fl ash
“2”
on the Status LED, and de-energize the exhauster for 60 minutes.
2.
When the 15 second pre-purge time has elapsed, the control energizes the Hot Surface Igniter (HSI)
output for a 5 second warm-up period (10 seconds on retries). The control energizes the main gas valve. 4
seconds after the gas is energized, the control de-energized the HSI output and leaves the gas energized
another 1 second for fl
ame proving. If fl
ame is present at the end of the trial for ignition time, the control
leaves the gas valve energized, inducer on high speed, and begins heat blower on delay.
3.
Blower off delay is handled by the control board. When the thermostat “W” call ends, the control de-
energizes the gas valve, and starts the blower off delay period.
4.8 VARIA
TIONS
If your system includes air conditioning, your thermostat (supplied by the installer) will likely have two switches.
The fi
rst switch is the system switch. The switch settings usually include HEA
T , COOL, and OFF
. Some
thermostats have system switches which include HEAT,
COOL, AUT
O, and OFF . The system switch must be in
the HEAT
or AUT
O position for the furnace to run.
The second switch is the fan switch. It usually has settings of ON and AUT
O. The fan switch may be in either
position when using the furnace. If the fan switch is set to ON, the main blower will run continuously.
