York YCAS0098EB, Installation Operation & Maintenance, Page: 20 / 184

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JOHNSON CONTROLS
Thermal Overload
Three PTC (positive temperature coefficient) thermistors
in the motor windings of each phase provides thermal
protection. The sensor resistance stays relatively con-
stant at 1k
Ω
until a temperature of 266°F (130°C) is
sensed. The sensor experiences a rapid rise in resistance
beyond this temperature. Whenever the resistance of one
of the sensors reaches 13k
Ω
, the 2ACE module trips,
which ultimately de-energizes the motor’s pilot circuit.
Reset is manual after the motor cools and the sensor
resistance drops to 3.25k
Ω
.
Current Imbalance (Loaded & Unloaded)/
Loss of Phase
A 2 second delay at start-up allows for any imbalances
resulting during normal starting conditions. After this
initial delay, the 2ACE module compares the “Oper-
ating Current” to the measured half line current. The
“Operating Current” is given by 0.65 X factory overload
current setting.
An
unloaded compressor condition occurs when any
measured half line current is less than the “Operating
Current.” A current imbalance exceeding an unloaded
level of 25% will result in the motor pilot circuit being
de-energized.
A
loaded compressor condition
occurs when any mea-
sured half line current is greater than or equal to the
“Operating Current.” A current imbalance exceeding a
loaded level of 17% will result in the motor pilot circuit
being de-energized.
Imbalance is defined as
(High Phase - Low Phase)/High Phase
Improper Phase Sequence
The 2ACE module calculates the phase sequence at
start-up using the three current transformers to deter-
mine whether the three phase sequence on the load
side of the main contactor is miswired. Upon detection
of a miswired motor load, the module will de-energize
the main contactor pilot circuit within 50 millisecond
response time.
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