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GROUNDING
CONNECTIONS
A common
ground
is required
for the burner, spark
igniter-sensor
mounting
bracket
and the GND terminal
of the 587. If ground
is poor or erratic, safety shutdown
may occur occasionally
even though
operation
is nor-
mal at time of checkout.
Therefore,
if nuisance
shut-
downs
have been reported,
be sure to check ground
connections.
Electrical
ground
connections
at the
spark
ig-
niter-sensor
and the S87D must be clean and tight. If
leadwire
is damaged
or deteriorated,
use only No. 14 or
No. 18 gauge,
moisture-resistant,
thermoplastic
in-
sulated
wire with
105 C [221 F] minimum
rating
as
replacement.
FLAME SENSOR CIRCUIT
The S87D provides
ac power
to the flame
sensor
which the burner flame rectifies to direct current.
If the
flame signal back to the S87 is not at least 1.5 uA dc, the
system will lock out.
The output
of the flame
sensing
circuit
can
be
checked
directly
on the S87D. Check the flame sensing
circuit as follows.
1. Connect
a meter
(dc microammeter
scale)
in
series with the sensor wire as shown in Fig. 9. Use the
Honeywell
Wl36A Test Meter or equivalent.
Disconnect
the sensor wire at the S87D. Connect the red (positive)
lead of the meter to the free end of the sensor wire.
Connect
the black (negative)
meter lead to the sensor
terminal
on the S87.
2. Restart the system and read the meter. The flame
sensor current
must be at least 1.5uA and steady. If the
reading
is less than 1.5 uA or unsteady,
see LOW OR
UNSTEADY FLAME CURRENT section, below.
FLAME SENSOR CURRENT CHECK-USE YA SCALE
FIG. g-S87
FLAME CURRENT MEASUREMENT.
LOW OR UNSTEADY FLAME CURRENT
If the current to the S87D flame circuit is less than 1.5
AIA or is unsteady,
check the burner
flame and flame
sensor location
and electrical
connections
as follows.
Burner Flame
The flame sensor
must be constantly
immersed
in
flame.
Check
burner
flame
conditions
as shown
in
Fig. 10. If necessary,
improve
the flame condition
or
relocate
the flame sensor to a place on the main burner
where flame conditions
are better.
Flame Sensor
The flame signal is best when about 1 in. [25.4 mm]
of flame rod is immersed
in the burner flame. A bent
flame rod or mounting
bracket
can affect flame signal.
Bend flame rod bracket to correct position if necessary.
Excess temperature
at the ceramic
flame rod insulator
may cause
leakage
to ground,
decreasing
the flame
signal. Replace the flame sensor if the ceramic insulator
is cracked,
and relocate
the sensor to an area of lower
ambient temperature
if necesary.
Electrical Connections
and Shorts
Connections
at the flame sensor must be clean and
tight.
If wiring
needs
replacement,
use
moisture-
resistant
No. 18 wire rated for continuous
dutv up to 105
_
C [221 F].
FIG. lo--BURNER
FLAME CONDITIONS.
CHECKOUT AFTER SERVICE
Perform
the following
steps before
leaving
the job
(described
in CHECKOUT section)-
* START SYSTEM
l
SAFETY LOCKOUT CHECK
. SAFETY LOCKOUT RESET
Also perform
any other checks recommended
by the
heating
appliance
manufacturer
if system components
other the the Y343B were serviced.
10
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