Honeywell R7795A Manual page 6

R7795A,B,C,D
DETAILED OPERATING SEQUENCE
Fig. 4—Operating sequence for the R7795C,D with interrupted pilot.
The R7795C,D provides the following operational se-
quence when used with the appropriate flame detector. (See
Figs. 4 and 5.)
STANDBY
The R7795 Primary Control is ready to start up when the
burner controller closes (limits are closed).
NORMAL START-UP
1. With power applied (limits and controller closed, ter-
minal L1 to 16, and no flame signal present), the 3K
relay pulls in and the burner motor (terminal 8) is energized.
2. As soon as the airflow switch closes (terminal 3 to
8), and with the RUN/TEST switch in the RUN posi-
tion, the ST795A Prepurge Timer starts to time out (pre-
purge begins).
NOTE: The ST795A Prepurge Timer returns to zero any
time the airflow switch opens or the RUN/TEST switch
is moved to the TEST position. The prepurge restarts
when the airflow switch recloses or the RUN/TEST
switch is returned to the RUN position.
3. At the end of prepurge (ST795A timed out), the 1K
and 4K relays pull in, simultaneously energizing the igni-
tion transformer (terminal 18) and the interrupted pilot
valve (terminal 5). This starts the ten or four second pilot
flame establishing period. Safety shutdown and lockout
will occur if presence of flame is not proven within:
• Ten seconds if the ORANGE jumper is not clipped.
• Four seconds if the ORANGE jumper is clipped.
If the RUN/TEST switch is moved to the TEST posi-
tion during the pilot flame establishing period, the se-
quence is stopped in trial for pilot flame. The safety switch
heater is energized during this pilot flame establishing
period whenever flame is not present. Safety shutdown
and lockout will occur if the absence of flame exceeds
15 seconds (nominal).
4. MAIN FLAME IGNITION TRIAL
At the end of the pilot flame establishing period (ten or
four seconds), with pilot flame present, and the RUN/TEST
switch in the RUN position, the ignition transformer (termi-
nal 18) is de-energized and the main valve (terminal 6) is
energized, starting the main flame ignition trial.
Ten seconds into the main flame ignition trial, the pilot
valve (terminal 5) is de-energized and the delayed main
valve (terminal 7) is energized. This completes the ten
second main flame ignition trial period.
The R7795 is now in the normal burner run mode of
operation and will remain so until an external command
directs it to do otherwise.
5. NORMAL SHUTDOWN
When the burner controller opens, the main valves
(terminals 6 and 7) and the burner/blower motor (termi-
nal 8) are immediately de-energized. The R7795 goes into
the standby mode, terminating the operating cycle.
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