Install Instructions

RM7898A 7800 SERIES VALVE PROVING PRIMARY RELAY MODULES
66-1161—04 16
Pre-Purge
The RM7898 Relay Module provides PREPURGE timing,
selectable with ST7800 Purge Timer cards, from two seconds
to thirty minutes with power applied and the operating control
indicating a call for heat.
1. The Airflow Interlock, burner switch, Run/Test switch
and all microcomputer-monitored circuits must also be
in the correct operating state.
2. The motor output, terminal 4, is powered to start the
PREPURGE sequence.
3. The Airflow Interlock input closes ten seconds into PRE-
PURGE or within the specified purge card timing; other-
wise, a recycle to the beginning of PREPURGE or
lockout occurs, depending on how the Airflow Switch
selectable jumper (JR3) is configured.
4. Valve Proving test occurs concurrent with Purge if fea-
ture Before, Both, or Split are selected.
Ignition Trials
1. Pilot Flame Establishing Period (PFEP):
a. When the PFEP begins:
(1) The pilot valve and ignition transformer,
terminals 8 and 10, are energized. The RM7898
has an interrupted pilot valve, terminal 8;
intermittent if terminal 19 is powered.
(RM7898A1018 shuts the ignition off when flame
is sensed.)
(2) Flame must be proven by the end of the ten
second PFEP (four seconds if Configuration
Jumper JR1 is clipped). If a flame is not proven
by the end of PFEP, a safety shutdown occurs.
(3) the Pre-Ignition Interlock is ignored throughout
the Trial for Ignition State.
2. Main Flame Establishing Period (MFEP):
a. After PFEP, and with the presence of flame,
the main fuel valve, terminal 9 (and 21 for Valve
Proving operation) is powered.
b. The RM7898 has a ten second MFEP. The
interrupted pilot valve, terminal 8, is de-energized
(with terminal 19 powered, terminal 8 will remain on
[intermittent pilot] throughout the run period).
(1) If flameout occurs, the RM7898 recycles to the
beginning of Purge. In VP mode, valve proving
testing will not repeat.
(2) If Configuration Resistor (JR2) is clipped, the
RM7898 will lockout and Postpurge if pro-
grammed. Valve Proving testing will be con-
ducted if Both, Split, or After option is selected.
3. Direct Spark Ignition with Valve Proving feature:
Demand Input is terminal 17 and Enable (120V power)
connected to terminal 18.
a. When this main flame establishing period begins:
(1) Ignition, Main Valve 1, and Main Valve 2 termi-
nals, 9, 10, and 21, are turned on simultane-
ously.
(2) Flame must be proven at the end of the 4-second
main flame establishing time. Ignition terminal 10
is shut off and system is in Run. The
RM7898A1018 will shut off the ignition when
flame is sensed, but the establishing period con-
tinues.
(3) If flame is not proven by the end of this main
flame establishing period, safety shutdown
occurs.
(4) The Pre-Ignition Interlock is ignored throughout
the trial for ignition period.
Run
The relay module is now in RUN and remains in RUN until the
controller input, terminal 6 (terminal 17 if in VPS mode),
opens, indicating that the demand is satisfied or a limit has
opened.
Post-Purge
After demand is satisfied or a limit opens, de-energizing
terminal 6 (terminal 17 if in VPS mode), Pilot valve, main valve
1, main valve 2, terminals 8, 9 and 21, are de-energized. The
blower motor, terminal 4, remains powered during the
specified programmed time. The Pre-Ignition Interlock closes
within the first five seconds of Post Purge.
The Valve Proving test is conducted concurrent with the Post-
Purge if options Split, Both or After are enabled.
Run/Test Switch
The Run/Test Switch is located on the top side of the relay
module, see Fig. 24. The Run/Test Switch allows the burner
sequence to be altered as follows:
1. In the measured PREPURGE sequence, the Run/Test
Switch, placed in the TEST position, causes the PRE-
PURGE timing to stop.
2. In the Pilot Flame Establishing Period, the Run/Test
Switch, placed in the TEST position, stops the timer
during the first eight seconds of a ten-second PFEP
selection or during the first three seconds of a
four-second PFEP selection. It also allows for pilot
turn-down test and other burner adjustments. This
activates a fifteen-second flameout timer that permits
pilot flame adjustment without nuisance safety
shutdowns. The Run/Test Switch is ignored during
PFEP if terminals
8 and 9 are jumpered.
IMPORTANT
When the relay module is switched to the TEST
mode, it stops and holds at the next Run/Test Switch
point in the operating sequence. Make sure that the
Run/Test Switch is in the RUN position before
leaving the installation.