54
SERVICING
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.
.
.
GND
GND
THIS IS L1 OR THE
HOT POWER LEG
THIS IS THE COMMON
OR NEUTRAL LEG
INCOMING POWER
CHECKING FOR PHASING - PRIMARY TO SECONDARY OF UNMARKED TRANSFORMERS*
TRANSFORMER
.
SECONDA
RY
PRIMA
RY
.
GND
C
R
LINE VOLTAGE
L1 (HOT)
LINE VOLTAGE
(NEUTRAL)
METER READS
24 VOLTS
METER READS
120 VOLTS
.
GND
C
R
N
L1
.
GND
C
R
N
L1
READS 96 VOLTS - IN PHASE
READS 144 VOLTS - OUT OF PHASE
.
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.
C
R
GN
D
NEUTRAL
L1
PHASING SYMBOL
24 V
120 V
These then should be wired to the furnace accordingly.
Some transformers will display phasing symbols as shown
in the illustration to the left to assist in determining proper
transformer phasing.