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Form O-CAUA, P/N 164772 R7, Page 9

Abnormal Heat Cycle

Functions

Interrupted Call for Heat - If the system controller call for heat is removed before the

ame is recognized, the circuit board will run the venter motor for the post purge period

and de-energize all outputs.

If the call for heat is removed after successful ignition, the circuit board will de-energize

the gas valve and run the venter motor through post purge.

Ignition Retry - If ame is not established on the rst trial for ignition period, the igni-

tion system circuit board de-energizes the gas valve, and the venter motor remains

energized for an inter-purge period of 10 seconds. The spark and gas valve are then

re-energized, and the circuit board initiates another trial for ignition.

If ame is not established on the second trial for ignition, the circuit board de-energizes

the gas valve and venter motor remains energized. The spark and gas valve are re-

energized and the circuit board initiates another trial for ignition.

If ame is not established on the third trial for ignition period, the circuit board de-

energizes the gas valve, and the venter motor remains energized for an inter-purge

period of 10 seconds. The circuit board then re-energizes the gas valve and spark and

initiates another trial for ignition.

If ame is not established on the fourth trial for ignition (initial try plus 3 re-tries), the

circuit board de-energizes the gas valve and goes into lockout. The circuit board goes

to one ash on the green LED to indicate ignition failure lockout.

Limit Switch Operation - The limit switch is ignored unless a call for heat is present

(W energized). If the limit switch is open and a call for heat is present, the control de-

energizes the gas valve, runs the blower motor on heat speed, and runs the induced

draft (venter) motor. The control will be in soft lockout and ashing fault code “3”,

before returning to normal operation.

When the limit switch re-closes or the call for heat is lost, the control runs the induced

draft motor through post purge and runs the blower through the selected fan off delay.

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 ignition system circuit board 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 circuit board will de-ener-

gize the gas valve. If ame is lost before the end of the 2 second pressure switch rec-

ognition delay, the circuit board will respond to the loss of ame. If the pressure switch

remains open for 2 seconds and the ame remains, the circuit board de-energizes the

gas valve and the venter motor runs through postpurge.

Power interruptions of less than 80mS shall not cause the circuit board to change

operating states. Power interruptions greater than 80mS may cause the circuit board

to interrupt the current operating cycle and re-start.

Ignition System

Fault Modes

Undesired Flame - If ame is sensed longer than 20 seconds while the gas valve is

de-energized, the circuit board shall energize the venter motor. When ame is no lon-

ger sensed, the venter motor will run through postpurge. The circuit board will do a soft

lockout, but will still respond to open limit and ame. The FLAME (yellow) LED shall

ash rapidly when lockout is due to undesired ame.

Gas Valve Relay Fault - If the circuit board senses the gas valve as energized for

more than one second when the circuit board 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 circuit board will lockout with the 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 ow

unless ame is present.

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 circuit board shall not initiate a call for heat while in lockout. The

circuit board will still respond to an open limit and undesired ame. Lockout shall auto-

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