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6-Cooling Contactor K1
K1 is a 24V to line voltage contactor used to energize the
compressor and condenser fan in response to thermostat
demand. Threephase units use threepoledoublebreak
contactors. Singlephase units use singlepole contac
tors.
DANGER - ALL SINGLEPHASE UNITS USE
SINGLEPOLE CONTACTORS. ONE LEG OF COM
PRESSOR, CAPACITOR AND CONDENSER FAN
ARE CONNECTED TO LINE VOLTAGE AT ALL
TIMES. POTENTIAL EXISTS FOR ELECTRICAL
SHOCK RESULTING IN INJURY OR DEATH. RE
MOVE ALL POWER AT DISCONNECT BEFORE
SERVICING.
NOTE - Contactor K1 is energized by the thermostat
control system. Depending on the control system
installed, the contactors may or may not be immediate
ly energized upon demand. Refer to the operation se
quence for the control system installed.
7-Indoor Blower Relay K3 (Cooling Speed)
208/230 volt units use a single 2PDT relay to energize the
indoor blower motor. 460 volt and 575 volt units use a
single 3PDT relay. The relay coil is energized by blower
demand from indoor thermostat terminal G" (cooling de
mand or fan switch in ON" position). When the coil is ener
gized, a set of N.O. contacts closes to energize the blower
motor on high speed. When deenergized, a set of N.C.
contacts allows the fan / limit control relay to energize the
blower on heating speed (refer to unit wiring diagram).
460 (G) and 575(J) voltage units use a unique blower mo
tor. The motor utilizes a set of N.C. relay K3 contacts to
complete an internal circuit when the motor is on low or
medium (heating) speed.
8-Potential Relay K31
Relay K31 is used in singlephase -510 and -650 units only
and is located in the control box. It is a potential relay
which controls the operation of the starting circuit. The
relay is normally closed when the compressor (contactor
K1) is deenergized. Capacitor (C7) is connected to a set
of N.C. K31 contacts and is used to assist the compressor
in starting. When K1 energizes, the compressor immedi
ately begins startup. K31 remains deenergized during
compressor startup and the start capacitor (C7) remains
in the circuit. As the compressor gains speed K31 is ener
gized by electromotive forces generated by the compres
sor. When K31 energizes, its contacts open to take the
start capacitor out of the circuit.
9-Combustion Air Blower Relay K13
Relay K13 is a DPDT relay located inside the control box.
K13 is energized by heating demand from the thermostat
and is energized throughout the heating demand. When
energized, K13 normally open contacts close to energize
the combustion air blower and begin a heating sequence.
A differential pressure prove" switch connected to the
combustion air blower in turn energizes the ignition control
and gas valve. A separate set of K13 contacts close to en
ergize the economizer.
10-Indoor Blower Relay K20
(Heating Speed)
used in 460V and 575V units only
Relay K20 is a 3PDT relay also located in the control box.
Relay K20 is energized when timedelay relay K25 closes.
K20 is used to energize the blower on heating speed.
When relay K20 is energized, a set of contacts close to en
ergize the blower.
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