present, the control de-energizes the gas valve and turns the fan/blower
motor on heat speed and runs the venter motor.
When the switch re-closes or the call for heat is lost, the control runs the
venter motor through post purge and runs the blower/fan motor through the
selected fan off delay. The control will return to normal operation after fan
off delay is completed.
Pressure Switch
- If the pressure switch opens before the trial for ignition
period, the venter motor will run through the pressure switch recognition
delay (2 seconds), the gas valve will be de-energized, and the venter motor
will run through the postpurge time. The control will re-start the heat cycle
at the pressure switch proving state if the call for heat still exists.
Pressure switch opening for less than 2 seconds during the trial for ignition
period shall not interrupt the heat cycle. (Gas valve will de-energize while
the pressure switch is open.)
If the pressure switch opens after a successful ignition, the control will de-
energize the gas valve. If flame is lost before the end of the 2 second pres
-
sure switch recognition delay, the control will respond to the loss of flame.
If the pressure switch remains open for 2 seconds and the flame remains,
the control de-energizes the gas valve, the venter motor runs through post-
purge, and the fan/blower motor runs on heat speed through the selected
fan off delay. When the fan off delay is over, the fan/blower motor is de-
energized, and a heat cycle is begun if the call for heat still exists.
When the thermostat calls for continuous fan (G) without a call for heat, the
fan motor is energized after a .25 second delay. NOTE: This brief on delay
is to allow the “G” terminal to energize slightly before “Y” and an external
changeover relay to switch from “G” to “W” without causing momentary
glitches in the fan/blower output. The fan remains energized as long as the
call for fan remains without a call for heat.
If a call for heat (W) occurs during continuous fan, the fan/blower will de-
energize.
A call for fan is ignored while in lockout.
Undesired Flame
- If flame is sensed longer than 20 seconds while the gas
valve is de-energized, the control shall energize the venter motor and fan/
blower motor on heat speed. When flame is no longer sensed, the venter
motor will run through postpurge, and the fan/blower motor will run through
the selected heat fan off delay time. The control will do a soft lockout, but
will still respond to open limit and flame. The FLAME (yellow) LED shall
flash rapidly when lockout is due to undesired flame.
Gas Valve Relay Fault
- If the control senses the gas valve as energized
for more than one second when the control is not attempting to energize
the gas valve, or the gas valve is sensed as not energized when it is sup-
posed to be energized, then the control will lockout with green LED off. The
control assumes either the contacts of the relay driving the gas valve have
welded shut, or the sensing circuit has failed. The venter motor is forced off
to open the pressure switch to stop gas flow unless flame is present.
If the gas valve was sensed as closed when it should be open, and has not
de-energized after the venter motor was shutoff for 15 seconds, then the
venter motor is re-energized to vent the unburned gas.
Abnormal Heat Cycle
Functions (cont’d)
10. Ignition System
(cont’d)
Fault Modes
Continuous Fan
Operation
Form I-UEAS, Page 36
