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First and second stage cooling operate independent of
each other and can modulate back and forth according to
the thermostat demand.
First Stage Cooling (Low Capacity)
1 - Cooling demand initiates at Y1 at the thermostat.
2 - Voltage from terminal Y passes through S4
high pressure switch, energizes K1 compressor
contactor, passes through the low pressure switch
(S87) and returns to common side of the 24VAC
power.
3 - K1 closes, energizing B1 compressor and B4
outdoor fan.
4 - Solenoid L34 is not energized so the slider ring
remains open, limiting compressor to low capacity.
Second Stage Cooling (High Capacity)
Compressor is operating in rst stage cooling. Second
stage thermostat demand sends voltage to rectier plug
D4. D4 converts the AC voltage to DC voltage and ener-
gizes L34 unloader solenoid. L34 closes the slider ring,
allowing the compressor to operate at high capacity.
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