connectors should read zero ohms while
the other should read infinity. Repeat with other
connector. The same female connector as before
should read zero while the other connector again reads
infinity. Reverse polarity on the ohmmeter leads
and repeat. The female connector that read infinity
previously should now read close to zero ohms.
Replace plug if either of these test methods
doesn’t show the desired results.
Unloader Test Procedure with CoreSense
If it is suspected that the unloader is not working, the
following methods may be used to verify operation.
1. Operate the system and measure compressor
amperage. Cycle the unloader on and off at ten
second intervals by applying and removing Y2
voltage to the module. Wait five seconds after
power is applied to Y2 before taking a reading.
An increase in compressor amperage should be
observed when switching from part-load to full-load
and a reduction in compressor amperage should
be observed when changing from full-load to part-
load. The percent change in current depends on
the operating conditions and voltage.
2. If Step 1 does not give the expected results remove
the solenoid plug from the compressor and with the
unit running and the thermostat calling for Y2 to be
energized test the voltage output at the plug with a
dc voltmeter. The reading should be 18 to 28 VDC for
CoreSense Diagnostics module. If not, unplug the
harness from the module and check voltage at the “DC
Sol” pins of the module. The module will not power the
unloader solenoid if the compressor is not running or
Fault Code 1 or 9 is active.
3. If the correct DC voltage is at the control circuit
molded plug measure the unloader coil resistance.
The solenoid coil should have continuity and not
be grounded or have infinite resistance. If the
coil resistance is infinite, zero, or grounded, the
compressor must be replaced.
For more information on service practices refer to
Service Procedures in AE4-1365.
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