Midco Economite RE6850B - Manual (Page 14)

Part 2 Service
For operation characteristics, maintenance, and service procedures, refer to
manufacturer's literature provided with burner.
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The standard RE6850 burner is equipped with a Honeywell RM7895 microprocessor
based burner control, employing a flame rectification system of flame detection. Burner
construction for special codes and/or insurance requirements such as Factory Mutual
or Industrial Risk Insurers (IRI) may require alternate controls. A safe start and run control
sequence is provided with instantaneous response to presence or loss of flame signal.
Flame failure response time is 3-seconds; Pilot Flame Establishing Period (PFEP) is field
selectable from 4 or 10-seconds. The RM7895 features a pre-purge time (30-seconds for
ON-OFF, 90-seconds for 2-Step or Modulating burners), and a plug-in amplifier. An airflow
circuit is also field selectable to allow either lockout or recycle upon loss of airflow. Five
LED’s (light emitting diodes) are provided to display sequence information. Refer to the
Honeywell RM7895 literature for detailed operating information, configuration requirements,
testing, and service.
INITIATE SEQUENCE ("POWER" LED is lit)
The RM7895 enters the INITIATE sequence when it is powered. The INITIATE
sequence lasts for ten seconds unless the voltage or frequency tolerances are not met
(refer to Honeywell RM7895 literature for criteria). When tolerances are met, the INITIATE
sequence will restart. If the conditions not corrected and the hold condition exists for four
minutes, the RM7895 will lock-out. Causes for hold conditions in the INITIATE sequence
are in the Honeywell RM7895 literature.
STANDBY ("POWER" LED is lit).
The RM7895 is idle in this state of sequencing. When the burner switch, limits, operating
limit controls, and all microprocessor monitored circuits are in the correct state for the
RM7895 to continue, sequencing will advance to PREPURGE.
PREPURGE ("POWER" LED is lit).
The RM7895 in this application features a prepurge time of 30-seconds for ON-OFF,
90-seconds for 2-Step or Modulating burners.
Once the STANDBY sequence has a "CALL FOR HEAT" input, normal start-up
prepurge will be initiated.
A. The blower motor is powered to start the prepurge sequence.
B. The airflow interlock switch must close in ten seconds of prepurge or within the
specified purge card timing. Otherwise a recycle to the beginning of prepurge
or lockout will occur, depending on how the airflow switch selectable jumper is
configured. Refer to Honeywell RM7895 literature for configuration requirements.
IGNITION TRIAL
1. PILOT FLAME ESTABLISHING PERIOD (PFEP)
A. The pilot valve and spark generator are energized.
B. 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.
2. MAIN FLAME ESTABLISHING PERIOD (MFEP)
After the ignition trials, and with the presence of flame, the main valve is energized.
("MAIN" LED will be lit.) If a flame-out occurs, the RM7895 will lockout or recycle within
3-seconds, depending on "jumper" configuration. Refer to Honeywell literature for proper
configuration.
The RM7895 is now in RUN mode and will remain in run mode until the controller input
opens, indicating that the call for heat has been satisfied or a limit has opened. Once this
occurs the RM7895 will sequence back to the STANDBY mode.
Notes: 1. During STANDBY and during RM7895 sequencing the "POWER" LED will
blink every four seconds. This is normal.
2. The "ALARM" LED will be lit in the event of any flame failure.
3. To maintain proper operation of this device it MUST be electrically grounded.
Refer to Honeywell RM7895 literature for criteria.
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Special equipment, either factory or contractor installed, may cause variation in the
procedures and descriptions given in this manual.
Consult the OEM's manual to identify the differences in the information.
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The major difference for the CUL version of the RE6700B / RE6850 / RE6850B is the French
/ English specification plate and the firing valve for the pilot line.
____________________________________________ 14
XVI Canadian
Specifications
XIII S8670J Ignition
Control Module
XIV Primary
Safety Control
RM7895
XV Special
Equipment
(OEM Versions)