Reznor PDH Operation Manual PreevA - Manual (Page 10)

Form O-PreevA, Page 10
3.0 Maintenance
Procedures
(cont’d)
3.3 Electrical
Compartment
(cont’d)
3.3.6 Ignition Control
Module Gas Heat
Section - applies
to all gas controls
except Options D12G
and AG58 (cont’d)
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 flame 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 flame is not established on the third trial for ignition period, the circuit board de-ener-
gizes 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 initi-
ates another trial for ignition.
If flame 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 flash 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 flashing 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 flame is lost before the end of the 2 second pressure switch rec-
ognition delay, the circuit board will respond to the loss of flame. If the pressure switch
remains open for 2 seconds and the flame remains, the circuit board de-energizes the
gas valve and the venter motor runs through postpurge.
Ignition System
Fault Modes
Undesired Flame - If flame is sensed longer than 20 seconds while the gas valve is
de-energized, the circuit board shall energize the venter motor. When flame 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 flame. The FLAME (yellow) LED shall
flash rapidly when lockout is due to undesired flame.
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 flow
unless flame 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 flame. Lockout shall auto-
matically reset after one hour. Lockout may be manually reset by removing power from
the circuit board for more than one second or removing the call for heat for more than
one and less than 20 seconds.
Hard Lockout - If the circuit board detects a fault on the board, the status LED will
be de-energized, and the circuit board 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 ignition system will self-
recover without lockout when voltage returns to the operating range.
Abnormal Heat Cycle Functions (cont’d)