Sequence Of Operation - Honeywell 7800 Series Installation Instructions Manual

i. Main valve terminal is energized.
j. Internal system fault occurred.
k. Purge card is removed.
l. Purge card is bad.
4. PILOT FLAME ESTABLISHING Period (PFEP):
a. Low Fire Switch opens.
b. Lockout Interlock opens.
c. Ignition/pilot valve terminal is not energized.
d. No flame is present at the end of PFEP.
e. Main valve terminal is energized.
f. Internal system fault occurred.
g. Purge card is removed.
h. Purge card is bad.
5. MAIN FLAME ESTABLISHING Period (MFEP):
a. Low Fire Switch Opens.
b. Lockout Interlock opens.
c. Ignition/pilot valve terminal is not energized.
d. Main valve terminal is not energized.
e. No flame is present at the end of MFEP.
f. Internal system fault occurred.
g. Purge card is removed.
h. Purge card is bad.
6. RUN Period:
a. No flame is present.
b. Lockout Interlock opens.
c. Main valve terminal is not energized.
d. Internal system fault occurred.
e. Purge card is removed.
f. Purge card is bad.
7. POSTPURGE Period:
a. Preignition Interlock does not close in five seconds
and opens after five-second time period.
b. Ignition/pilot valve/intermittent pilot valve terminal is
energized.
c. Main valve terminal is energized.
d. Internal system fault occurred.
e. Purge card is removed.
f. Purge card is bad.
OPERATION

Sequence of Operation

The RM7845A has the following operating sequences, see
Fig. 2, 3, 4, and Table 6. The RM7845A LED provide positive
visual indication of the program sequence: POWER, PILOT,
FLAME, MAIN and ALARM.
Initiate
The RM7845A enters the INITIATE sequence when the Relay
Module is powered. The RM7845A can also enter the
INITIATE sequence if the Relay Module verifies voltage
fluctuations of +10/-15 percent or frequency fluctuations of
±10 percent during any part of the operating sequence. The
INITIATE sequence lasts for ten seconds unless the voltage or
frequency tolerances are not met. When the tolerances are
not met, a hold condition is initiated and displayed on the VFD
for at least five seconds. When the tolerances are met, the
INITIATE sequence restarts. If the condition is not corrected
RM7845A 7800 SERIES RELAY MODULES
and the hold condition exists for four minutes, the RM7845A
locks out. Causes for hold conditions in the INITIATE
sequence:
a. AC line dropout is detected.
b. AC line noise prevents a sufficient reading of the
line voltage inputs.
c. Low line voltage brownouts occur.
The INITIATE sequence also delays the burner motor starter
from being energized and de-energized from an intermittent
AC line input or control input.
Standby
The RM7845A is ready to start an operating sequence when
the operating control determines a call for heat is present. The
burner switch, limits, operating control and all microcomputer
monitored circuits must be in the correct state for the
RM7845A to continue into the PREPURGE sequence.
Normal Start-Up Prepurge
The RM7845A provides a prepurge timing selectable from two
seconds to 30 minutes with power applied and the RM7845
operating control indicating a call for heat:
a. Burner Switch, Run/Test Switch, Lockout Interlocks
and all microcomputer monitored circuits must be in
the correct operating state.
b. The blower motor output, terminal 5, is powered to
start the PREPURGE sequence. The firing rate
motor is driven to the high fire position. The
PREPURGE timing for the does not begin until the
Lockout Interlock String and High Fire Switch are
both closed.
c. The Preignition Interlock input must remain closed
throughout PREPURGE; otherwise, control returns
to the STANDBY state and holds (30 seconds) for
the RM7845A or safety shutdown for the RM7845A
occurs.
d. The Lockout Interlock or Running Interlock inputs
(interlock circuit including Airflow Switch) must close
by ten seconds into PREPURGE; otherwise, a
recycle to the beginning of PREPURGE for the
RM7845A will happen or a safety shutdown for the
RM7845A occurs.
e. When PREPURGE timing is complete, the firing rate
motor drives to the low fire position,
RM7845A.
f. When the firing rate motor reaches low fire position,
the Low Fire Switch, terminal 18, input must be
energized before entering the Ignition Trial state.
Ignition Trials
1. Pilot Flame Establishing Period (PFEP):
a. With the firing rate motor at the low fire position:
(1) The pilot valve and ignition transformer is
energized.
(2) During PFEP, the Low Fire Switch must remain
closed. If it opens, a safety shutdown occurs.
(3) The Preignition Interlock input is ignored
throughout the Ignition Trial state.
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