Applied Air GAS-FIRED HEATERS, Installation & Operation Instruction

Page: 33 / 64

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SECTION VII - TROUBLE SHOOTING
continued
Causes for hold conditions in the INITIATE sequence:
1. AC line dropout detection.
2. AC line noise that can prevent a suffi cient reading of
the line voltage inputs.
3. Low line voltage brownouts.
The INITIATE sequence also delays the burner motor
starter from being energized and de-energized from an
intermittent AC line input or control input.
Standby
The RM7897A 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 relay module to continue
into the PREPURGE sequence.
Normal Start-Up Prepurge
The RM7897A Relay Module provides PREPURGE
timing selectable from two seconds to thirty minutes
with power applied and the operating control indicating
a call for heat.
1. The Airfl ow 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 Airfl ow Interlock input closes ten seconds into
PREPURGE or within the specifi ed purge card
timing; otherwise, a recycle to the beginning of
PREPURGE or lockout occurs, depending on how
the Airfl ow Switch selectable jumper (JR3) is confi g-
ured.
Ignition Trials
1. Pilot Flame Establishing Period (PFEP):
a. When the PFEP begins:
(1) The pilot valve and ignition transformer,
terminal 21 is energized. The RM7897A has
an intermittent pilot valve, terminal 8 and inter-
rupted pilot valve, terminal 21.
(2) Flame must be proven by the end of the ten
second PFEP (four seconds if Confi guration
Jumper JR1 is clipped) to allow the
sequence to continue. If a fl ame is not proven
by the end of PFEP, a safety shutdown occurs.
(3) The pre-ignition inter lock is ignored
throughtout the trial for ignition state.
2. Main Flame Establishing Period (MFEP):
a. After PFEP, and with the presence of fl ame, the
main fuel valve, terminal 9, is powered. If a fl ame-
out occurs, the relay module locks out or recycles
(depending on status of jumper JR2) within 0.8
or 3 seconds, depending on the Flame Failure
Response Time (FFRT) of the amplifi er.
b. The RM7897A (terminal 21) has a ten second
MFEP. After the Ignition Trials, the interupted pilot
valve, terminal 8 is de-energized. If a fl ameout
occurs, the relay module locks out or recycles
(depending on status of jumper JR2) within 0.8
or 3 seconds, depending on the amplifi er FFRT.
Run
1. The RM7897C has a delayed main valve that is en-
ergized once the RUN period is entered.
2. The relay module is now in RUN and remains in
RUN until the controller input, terminal 6, opens,
indicating that the demand is satisfi ed or a limit has
opened.
Post Purge
After demand is satisfied or a limit opens,
de-energizing terminal 6, the Ignition/Pilot valve,
main valve and delayed main valve, terminals 8, 9,
and 21 are de-energized. The blower motor, terminal
4, remains powered during the specifi ed programmed
time. The Pre-Ignition Interlock closes within the fi rst fi ve
seconds of Post Purge.
Run/Test Switch
The Run/Test Switch is located on the top side of the
relay module, see Fig. 4. 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
PREPURGE timing to stop.
2. In the Pilot Flame Establishing Period, the Run/
Test Switch, placed in the TEST position, stops the
timer during the fi rst eight seconds of a ten-second
PFEP selection or during the fi rst three seconds
of a four-second PFEP selection. It allows for pilot
turn-down test and other burner adjustments. This
activates a fi fteen-second fl ameout timer that per-
mits pilot fl ame adjustment without nuisance safety
shutdowns. The Run/Test Switch is ignored during
PFEP for the C relay module if terminals 8 and 9 or
9 and 21 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.