RM7890, RM7895 100 Vac
condition is not corrected and the hold condition exists for
four minutes, the relay module locks out. Causes for hold con-
ditions in the INITIATE sequence are:
1 .
Ac line dropout is detected.
2 .
Ac line frequency error.
3 .
Ac line noise occurred that prevents a sufficient reading of
the line voltage inputs.
4 .
Brownout occurred caused by a low line voltage.
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 relay module is ready to start an operating sequence
when the operating control input determines a call for heat is
present. The burner switch, limits, operating limit control and
all microcomputer monitored circuits must be in the correct
state for the relay module to continue into the SAFE-START
CHECK (RM7890) or the PREPURGE (RM7895) sequence.
Normal Startup
Safe-Start Check
The RM7890, RM7895 verify that a flame does not exist and
proceeds into the Ignition Trial. If a flame is present, the relay
module recycles to the STANDBY period. If the critical loads
are not in the correct state, a safety shutdown occurs.
Prepurge (RM7895)
The RM7895 provides a selectable PREPURGE timing from
two seconds to thirty minutes (using the ST7800 Plug-in
Purge Timer) with power applied and the RM7895 operating
control indicating a call for heat.
1 .
Airflow Interlock, burner switch and all microcomputer
monitored circuits must be in the correct operating state.
2 .
The blower motor output, terminal 4, is powered to start
the PREPURGE sequence.
3 .
The Airflow Interlock input must close ten seconds into
PREPURGE or within the specified purge card timing; oth-
erwise, a recycle to the beginning of PREPURGE or lockout
occurs depending on how the airflow switch selectable
jumper is configured.
Ignition Trials
Pilot Flame Establishing Period (PFEP):
1 .
The pilot valve and ignition transformer, terminals 8 and
10, are energized. The relay module has an intermittent pi-
lot valve, terminal 8.
2 .
Flame must be proven by the end of the 4- or
10-second PFEP to allow the sequence to continue. If
flame is not proven by the end of PFEP, a safety shutdown
occurs. For the RM7890 only: if the flame is established
within the PFEP, the system immediately goes to the RUN
state.
3 .
With flame proven (RM7895 reaches the end of the PFEP),
the ignition, terminal 10, is de-energized and the main
valve, terminal 9, is energized.
Run
The relay module is now in RUN and remains in RUN until ter-
minal 6, the controller input, opens, indicating that the call for
heat demand is satisfied or that a limit has opened.
Selectable Site-Configurable Jumpers
The RM7890 has two site-configurable jumper options and
the RM7895 has three. See Fig. 16 and Tables 8 and 9. The
site-configurable jumpers should be clipped with side cutters
and the resistors removed from the relay module.
SERVICE NOTE: For RM7890 when using a 3-second am-
plifier, clip and remove site-configurable
jumper JR2 . If not removed, an F46 Lock-
out occurs .
IMPORTANT
Clipping jumpers after 200 hours of operation will result in a
hard lockout (Fault Code 110).
Fig. 16. Selectable site-configurable jumpers (RM7895
shown).
Table 9. Site-Configurable Jumper Options (RM7890).
Jumper Number
Description
Intact
Clipped
JR1
Pilot Flame Establishing Period
10 seconds
4 seconds
JR2
Flame Failure Action
Relight
a
Lockout
a
The Relight feature (JR2) requires a 0.8 second FFRT flame amplifier.
32-00216-01
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