Honeywell 7800 Series Installation Instructions Manual page 18

RM7838B,C 7800 SERIES RELAY MODULE
Standby
The RM7838B,C remains in STANDBY until the Burner
Control Switch is closed. Two seconds before leaving
STANDBY, the shutter circuit is energized and verifies that
no flame is present. The Alarm, terminal 3, is energized
until flame is sensed (RM7838B only).
Purge
The RM7838B,C provides PURGE timing selectable from
two seconds to thirty minutes. The RM7838C requires the
ST7800C Purge Timer for correct operation. The ST7800C
Purge Timer will not function with an RM7838B.
1. Closing the burner control switch starts the
recirculating/exhaust blower. PURGE sequence
begins when power is applied to the RM7838B,C
through the recirculating/exhaust blower airflow
switch, Stop Station, and the limit string to terminal
6. The Run/Test switch and all microcomputer-
monitored circuits must also be in the correct
operating state.
2. The RM7838B,C Relay Module commands the firing
rate motor to the high purge rate position by closing
a circuit between terminals 12 and 13. PURGE
timing begins when the High Fire Switch closes,
providing input to terminal 19. Four minutes, 15
seconds are provided for the High Fire Switch to
close. A jumpered High Fire Switch adds 30 seconds
to the PURGE timing.
3. When the PURGE timing is complete, the
RM7838B,C commands the firing rate motor to the
low fire position by closing a circuit between termi-
nals 13 and 14 (terminals 13 and 15 for the
RM7838C1020/RM7838C2020). Four minutes, 15
seconds are provided for the motor to reach the low
fire position.
4. When the Low Fire Proving Switch is proven (input
on terminal 18), the RM7838B,C commands the
Combustion Blower to turn on through terminal 5. A
jumpered Low Fire Switch adds 30 seconds to the
PURGE timing.
5. The RM7838C will wait indefinitely for the Combus-
tion Airflow Switch , terminal 7, to close. Once closed,
five seconds are provided for it to stabilize. Safety
shutdown occurs if the Combustion Blower Airflow
Switch opens after this five-second period, during
ignition trials or RUN.
6. The RM7838B,C waits indefinitely for the Start Input
to terminal 21.
7. The Preignition Interlock must remain closed
throughout PURGE timing or a safety shutdown
occurs.
8. The Alarm is powered during PURGE timing
(RM7838B only).
Ignition Trials
Ignition trials begin when the momentary Start input is
received at terminal 21 of the RM7838B,C. The
RM7838B,C locks out if the Start Switch is not released.
32-00199—01
1. Pilot Flame Establishing Period (PFEP):
a. When the PFEP begins:
(1) The pilot valve and ignition transformer,
terminals 8 and 10, are energized.
(2) Five seconds into PFEP, Ignition terminal 10
is de-energized.
(3) Flame must be proven by the end of the ten
second PFEP (four seconds if Configuration
Jumper JR1 is clipped); to allow the sequence
to continue. If a flame is not proven by the
end of PFEP, a safety shutdown occurs.
(4) During PFEP, the Low Fire Switch must
remain closed. If it opens, a safety shutdown
occurs.
(5) The Preignition Interlock input is ignored
throughout the Ignition Trial state.
(6) The alarm output stops when flame is
proven. (RM7838B only)
(7) The RM7838B,C (except
RM7838C1020/RM7838C2020):
(a)holds indefinitely, waiting for Manual Open
Valve command (terminal 17).
(b)holds indefinitely with a Pilot Valve Hold
command present on terminal 16.
(c)automatically sequences to Main Flame
Establishing Period (MFEP) if the
configuration jumper JR3 was clipped and
the Pilot Valve Hold Command is not
present. Manual Open Valve input, terminal
17, must be closed at the end of MFEP.
b. With flame proven, the alarm, terminal 3, is
de-energized (RM7838B only).
2. Main Flame Establishing Period (MFEP) (except
C1020 as it does not have a manual open valve
switch input):
a. With the configuration jumper JR3 intact, the
RM7838B,C waits for Manual Open Valve Switch
input to terminal 17 through a Manual Open
Valve Switch. With the configuration jumper JR3
clipped and the Pilot Valve Hold command on
terminal 16 open, the RM7838B,C initiates
immediate MFEP.
(1) Main valve terminal 9 is energized by the
RM7838B,C and the relay module is in the
RUN period.
(2) If configuration jumper JR2 is clipped, ten
seconds after terminal 9 is energized (15 sec-
onds for the RM7838C1004/RM7838C2004,
5 seconds for the
RM7838C1020/RM7838C2020), the pilot
valve terminal 8 is de-energized. If flame is
lost during this MFEP, safety shutdown
occurs and the ALARM sounds.
(3) If configuration jumper JR3 is clipped, a Man-
ual Open Valve Switch input must be present
at terminal 17 at the end of the MFEP or
safety shutdown occurs and the Alarm
sounds.
b. The RM7838C1020/RM7838C2020 proceeds
immediately to a 5 sec MFEP.
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