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SERVICING
As more and more electronic's are introduced to the Heat-
ing Trade, Polarization of incoming power and phasing of
primary to secondary voltage on transformers becomes
more important.
Polarization has been apparent in the Appliance industry
since the introduction of the three prong plug, however,
the Heating Industry does not use a plug for incoming
power, but is hard wired.
Some of the electronic boards being used today, with
flame rectification, will not function properly and/or at all
without polarization of incoming power. Some also require
phasing between the primary and secondary sides of step-
down transformers.
CHECKING FOR PHASING - PRIMARY TO SECONDARY OF UNMARKED TRANSFORMERS*
If meter reads approximately 96 volts - the primary to secondary are in phase - if reads approximately 144 volts out of
phase - reverse low voltage wires.
*NOTE: For flame rectification the common side of the secondary voltage (24 V) is cabinet grounded. If you were to
bench test a transformer the primary neutral and secondary common must be connected together for testing purposes.
C
24 V
R
PHASING SYMBOL
METER READS
24 VOLTS
.
.
.
.
.
.
VOLT / OHM
METER
TRANSFORMER
C
R
LINE VOLTAGE
L1 (HOT)
VOLT / OHM
METER
NEUTRAL
120 V
L1
METER READS
120 VOLTS
VOLT / OHM
METER
THIS IS L1 OR THE
HOT POWER LEG
These then should be wired to the furnace accordingly.
METER READS
120 VOLTS
VOLT / OHM
METER
LINE VOLTAGE
(NEUTRAL)
READS 144 VOLTS - OUT OF PHASE
Some transformers will display phasing symbols as shown
in the illustration to the left to assist in determining proper
transformer phasing.
Checking for polarization and phasing should become a
habit in servicing. Let's start now.
NOTE: PCBBF139 ignition control has a diagnostic flash
code for reversed polarity.
INCOMING POWER
METER READS
0 VOLTS
VOLT / OHM
METER
C
N
R
L1
VOLT / OHM
METER
READS 96 VOLTS - IN PHASE
C
N
R
L1
VOLT / OHM
METER
THIS IS THE COMMON
OR NEUTRAL LEG
17
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