Intertek GMVC96 - SERVICING PROCEDURES; Transformer Phasing and Voltage Checks

SERVICING
57
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.
THIS IS L1 OR THE
HOT POWER LEG
INCOMING POWER
THIS IS THE COMMON
OR NEUTRAL LEG
METER READS
120 VOLTS
METER READS
0 VOLTS
GND
GND
VOLT / OHM
METER
VOLT / OHM
METER
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.
.
.
.
.
.
.
VOLT / OHM
METER
G
N
D
PRIMARY
SECONDARY
TRANSFORMER
R
C
METER READS
24 VOLTS
LINE VOLTAGE
(NEUTRAL)
LINE VOLTAGE
L1 (HOT)
VOLT / OHM
METER
METER READS
120 VOLTS
VOLT / OHM
METER
C
R
G
N
D
N
L1
VOLT / OHM
METER
READS 96 VOLTS - IN PHASE
C
R
G
N
D
N
L1
VOLT / OHM
METER
READS 144 VOLTS - OUT OF PHASE
C
R
G
N
D
NEUTRAL
L1
PHASING SYMBOL
24 V
120 V