Honeywell 7800 SERIES RM7895A Manual Download

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Operation

RM7895A,B,C,D

OPERATION

Sequence of Operation

The RM7895 has the following operating sequences,

see Figs. 15, 16 and 18.

INITIATE

The RM7895 enters the INITIATE sequence when the

Relay Module is powered. The RM7895 can also enter the
INITIATE sequence if the Relay Module verifies voltage
fluctuations of +10/-15% or frequency fluctuations of
+/- 10% 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 will be initiated and will be
displayed on the optional VFD for at least five seconds. When
the tolerances are met, the INITIATE sequence will restart.
If the condition is not corrected and the hold condition exists
for four minutes, the RM7895 will lockout. Causes for hold
conditions in the INITIATE sequence are:

• AC line dropout is detected.
• AC line frequency error caused by using a 60 Hz device

on a 50 Hz line, or vice versa.

• AC line noise that can prevent a sufficient reading of

the line voltage inputs.

• Brownouts caused by a low line voltage.
The INITIATE sequence also delays the burner motor

starter from being energized and de-energized from an inter-
mittent AC line input or control input.

STANDBY

The RM7895 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 RM7895 to continue into the PRE-
PURGE sequence.

NORMAL START-UP
PREPURGE

The RM7895 provides a selectable PREPURGE timing

from two seconds to 30 minutes with power applied and
the RM7895 operating control indicating a call for heat.

a. Airflow Interlock, burner switch, Run/Test Switch and

all microcomputer monitored circuits must be in the
correct operating state.

b. The blower motor output, terminal 4, is powered to

start the PREPURGE sequence.

c. The Airflow Interlock input must close ten seconds

in PREPURGE or within the specified purge card
timing; otherwise, a recycle to the beginning of PRE-
PURGE or lockout will occur depending on how the
airflow switch selectable jumper is configured.

IGNITION TRIALS
a. Pilot Flame Establishing Period (PFEP):

1. The pilot valve and ignition transformer, terminals 8

and 10, are energized. The RM7895A,B has an inter-
mittent pilot valve, terminal 8. The RM7895C,D has
an interrupted pilot valve, terminal 8.

2. Flame must be proven by the end of the 4 or 10 sec-

ond PFEP (RM7895C1020 has a fixed ten second
PFEP) to allow the sequence to continue. If flame is
not proven by the end of PFEP, a safety shutdown
occurs.

3. At the end of PFEP, the ignition, terminal 10, is de-

energized. For RM7895A1048 and RM7895C1020
only, when flame is proven, the ignition, terminal 10,
is de-engergized. If the flame is lost and still in PFEP
the ignition, terminal 10, is re-energized.

Fig. 15—RM7895A,B sequence.

FOR RM7895A1048 (ONLY) IGNITION TERMINAL 10 IS DE-ENERGIZED WHEN FLAME IS PROVEN.

AIRFLOW SWITCH CHECK FEATURE IS FOR THE RM7895B.

POWER

LED
DISPLAY

OPERATING
CONTROLS
AND
INTERLOCKS

BURNER

FLAME
SIGNAL

INITIATE

POWER

STANDBY

POWER