Form I-UDA, P/N 195673 Rev 13, Page 6
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 pressure 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” termi
-
nal 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 supposed 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 pres
-
ent.
If the gas valve was sensed as closed when it should be open, and has not de-ener
-
gized after the venter motor was shutoff for 15 seconds, then the venter motor is re-
energized to vent the unburned gas.
Soft Lockout
- The control shall not initiate a call for heat or call for continuous fan
while in lockout. The control will still respond to an open limit and undesired flame.
Lockout shall automatically reset after one hour. Lockout may be manually reset by
removing power from the control for more than one second or removing the thermostat
call for heat for more than one and less than 20 seconds.
Hard Lockout
- If the control detects a fault on the control board, the status LED will be
de-energized, and the control will lockout as long as the fault remains. A hard lockout
will automatically reset if the hardware fault clears.
Power Interruption
- During a momentary power interruption or at voltage levels below
the minimum operating voltage (line voltage or low voltage) the system will self-recover
without lockout when voltage returns to the operating range.
Power interruptions of less than 80mS shall not cause the control to change operating
states. Power interruptions greater than 80mS may cause the control to interrupt the
current operating cycle and re-start.
Lockout
Fault Modes
Continuous Fan
Operation
8. Controls and
Operation
(cont’d)
8.3 Ignition System
(cont’d)
Abnormal Heat Cycle Functions (cont’d)
