66389-BIM-C-1208
36
Johnson Controls Unitary Products
During the flame stabilization period, a loss of the flame for 2
seconds will cause the main valves to close and the retry
operation to begin. After the flame stabilization period, a loss
of flame for 3/4 second will cause the main valves to close
and the retry operation to begin.
At the conclusion of the flame stabilization period, the ICB will
operate the gas heat in high fire (both valves open) for an
additional 100 seconds (for a total for 120 seconds of high fire
operation). After this 100 seconds, the ICB will then use the
call for the second stage of heat to control the second main
valve of the GV.
When “W1” is satisfied, both valves are closed.
SECOND STAGE OF HEATING
When the ICB receives a call for the second stage of heating,
“W2,” the ICB conducts a complete first stage ignition
sequence. If this sequence is satisfied, the second main
valve of the GV is opened.
When “W2” is satisfied, the second main valve is closed.
RETRY OPERATION
When a flame is lost or is not detected during an attempt to
achieve ignition, a retry operation occurs. A 30-second purge
is performed between ignition attempts.
If the unit fails after three ignition attempts, the furnace is
locked-out for one hour. The furnace is monitored during this
one-hour period for unsafe conditions.
RECYCLE OPERATION
When a flame is lost after the flame stabilization period, a
recycle operation occurs. If the unit fails after five recycle
attempts, the furnace is locked-out for one hour.
GAS HEATING OPERATION ERRORS
LOCK-OUT
A one-hour lockout occurs following three retries or five recy-
cles. During the one-hour lockout, flame detection, limit con-
ditions, and main valves are tested. Any improper results will
cause the appropriate action to occur. Recycling the low volt-
age power cancels the lock-out.
TEMPERATURE LIMIT
If the UCB senses zero volts from the high temperature limit,
the indoor blower motor is immediately energized. When the
UCB again senses 24 volts from the temperature limit, the
draft motor will perform a 15-second post-purge and the
indoor blower will be de-energized following the elapse of the
fan off delay for heating.
This limit is monitored regardless of unit operation status, i.e.
this limit is monitored at all time.
If the temperature limit opens three times within one hour, it
will lock-on the indoor blower motor and flash code is initiated
(See Table 29).
FLAME SENSE
Flame sensing occurs at all times. If “W1” is not present and
a flame is sensed for 2 seconds, the draft motor is energized
and the main valve is kept off. The ICB halts any operation
until a flame is not detected. Once the flame detection is lost,
the ICB performs a post-purge. Normal operation is allowed
concurrently with the purge (i.e. this purge can be considered
the purge associated with a call for “W1”).
If “W1” is present, a flame is sensed, but the main valve is not
energized, the draft motor is energized until the flame detec-
tion is lost. Normal operation is now allowed.
The flame detection circuitry continually tests itself. If the ICB
finds the flame detection circuitry to be faulty, the ICB will not
permit an ignition sequence. Also, the draft motor is ener-
gized. If this failure should occur during an ignition cycle the
failure is counted as a recycle.
GAS VALVE
The UCB and ICB continuously monitor the GV.
If the ICB senses voltage at the GV when not requested, the
ICB will energize the draft motor. The ICB will not operate the
furnace until voltage is no longer sensed at the GV. The draft
motor is stopped when voltage is not sensed at the GV.
Any time the UCB senses voltage at the GV without a call for
heat for a continuous five-minute period, the UCB will lock-on
the indoor blower and a flash code is initiated (Table 29).
When voltage is no longer sensed at the GV, the UCB will de-
energize the indoor blower following the elapse of the fan off
delay for heating.
If voltage has been sensed at the GV for at least 15 seconds
during the fan on delay for heating and GV voltage or “W1” is
lost, the indoor blower is forced on for the length of the fan off
delay for heating.
During a call for heat, if the UCB does not sense voltage at
the GV for a continuous five-minute period the UCB will initi-
ate a flash code (Table 29). The indoor blower motor will not
be locked-on while there is no GV voltage.
However, if during a normal ignition sequence, the NPC has
been tested to be open, IDM energized, NPC closes and then
the first stage main valve (MV1) is detected as being on, the
ignition sequence stops and the IDM is de-energized. (Since
the NPC is wired serially with the main valve relays, de-ener-
gizing the IDM will open the NPC). This failure is counted as
a recycle and will result in an eventual recycle lockout. If the
main valve continues to be energized after the IDM is de-
energized the IDM is re-energized. The second stage (MV2)
main valve is not monitored for closure after energization.
