12. If the signal increases above 5.3 VDC, the SC30
relay closes powering terminal 6 on the TR1 and
starts a second time delay of 15 seconds. At the end
of this time delay the fan switches to high speed (FR
LED lit) and the second stage gas valve opens (CR
LED lit) through the TR1 (terminal 9), provided the
high air switch contacts are closed. The manifold
pressure will vary from 1.4” w.c. to 3.5” w.c. in this
mode.
13. During heating operation, the thermostat, pressure
switch and main burner flame are constantly moni-
tored by the IC to assure proper system operation.
14. Operation continues in the high fire mode until the
controller input signal to the SC30 control drops to
4.7 VDC. At this point the SC30 relay circuit opens
(SC30 terminal 5 has no output) de-energizing the
second stage valve and the TR1 switches the com-
bustion blower to low speed operation. Low fire
modulation will continue as in Step 11.
15. When the thermostat (temperature controller) is sat-
isfied and the demand for heat ends, the heat enable
contact opens and the first stage valve is de-ener-
gized immediately, the control senses loss of flame
and a 30 second post-purge occurs (at high speed)
before de-energizing the combustion blower.
Ignition and Operational Failures During a Call for
Heat Result in Lockout of the Ignition Control
1. If flame is lost during an operational cycle, the control
will respond within 0.8 seconds. The spark will be
energized for a trial for ignition period to attempt to
re-light burners and prove flame sensor. If flame is
re-established, normal operation resumes
2. If the burners fail to light or carryover during a trial for
ignition, the control will attempt two additional igni-
tion trials. If no flame is present at the flame sensor
within 10 seconds, the spark and gas valve will be
de-energized. A 15 second inter-purge period begins
and the combustion blower continues to run. After
the inter-purge period another ignition trial will take
place.
3. If burner fails to light or prove the flame sensor fol-
lowing the two additional trials the control will go into
lockout. The valve relay in the IC will be de-energized
shutting of the gas valve immediately and the com-
bustion blower following a 30 second post-purge
period.
Recovery from Lockout
1. If the thermostat (controller) is still calling for heat one
hour after a lockout occurs, the control will automati-
cally reset and initiate a call for heat sequence.
2. The ignition control may also be manually reset, by
turning the thermostat (controller) down and back up
to previous temperature setting or removing power
(24V) to IC terminal 24 VAC.
IC Fault Conditions and LED Key
LED Steady On
Internal control fault
1 Flash
Combustion airflow fault
2 Flash
Flame with no call for heat
3 Flash
Ignition lockout
LED flashes on for ¼ second, and off for ¼ second dur-
ing fault condition. Pause between fault codes is three
seconds.
Refer to Table K3 for further LED code troubleshooting.
VCES-VHC-IOM-1F – VHC-36, -42 & -50
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