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crankcase thereby preventing liquid migration and subsequent
compressor damage. The insert type heater is self regulating. It is
connected electrically to the contactor L1 and L2 terminals.
Condenser Motor
This item is activated by the contactor during heating and cooling,
except during defrost and emergency heat operation.
Compressor
This item is activated by the contactor for heating and cooling,
except during emergency heat. It is protected by an internal over-
load.
Contactor Relay
This control is activated by the thermostat (24V coil) and supplies
power to the compressor and condenser fan motor.
Defrost Control
The Defrost control provides time/temperature initiation and termi-
nation of the defrost cycle. When a Defrost cycle is initiated, the
defrost control shifts the reversing valve to "COOLING" mode, stops
the outdoor fan and brings on supplemental heat. Normally, a
Defrost cycle will take only 2-3 minutes unless system is low on
charge or outdoor conditions are severe. (windy and cold). The
defrost control also provides for a 3 minute off cycle compressor
delay.
Outdoor Thermostat
These optional controls are used to prevent full electric heater
operation at varying outdoor ambient (0° F-to 45° F). They are nor-
mally open above their set points and closed below to permit stag-
ing of indoor supplement heater operation. If the outdoor ambient
temperature is below 0° F (-18° C) with 50% or higher RH, an
outdoor thermostat (OT) must be installed and set at (0°) on the
dial. Failure to comply with this requirement may result in damage
to the product which may not be covered by the manufacturer's
warranty.
Reversing Valve Coil
This coil is activated by the thermostat, in the cooling mode and
during defrost. It positions the reversing valve pilot valve for cooling
operation.
Indoor Blower Motor
This is activated by the room thermostat by COOLING or FAN ON
position. The motor is energized through the EBTDR for PSC mo-
tors and directly by the room thermostat for EEM motors (4 or 5 Ton
units). EEM motors are constant torque motors with very low power
consumption. This motor is energized by a 24V signal from the
thermostat. (See Air Flow Measurement and Adjustment for speed
adjustment instructions).
Blower Interlock Relay (Single Phase PSC Models Only)
This relay is used to energize the blower during the electric heat
operation. Some room thermostats do not energize the motor dur-
ing electric heat. This relay insures blower operation when the
room thermostat energizes heat. This relay has a 240 volt coil and
an 8 amp contact relay. This relay is energized by the electric heat
kit sequencer.
HEAT PUMP OPERATION
C
C
OOLING
YCLE
When the heat pump is in the cooling cycle, it operates exactly as
a Summer Air Conditioner unit. In this mode, all the charts and
data for service that apply to summer air conditioning apply to the
heat pump. Most apply on the heating cycle except that "condenser"
becomes "evaporator", "evaporator" becomes "condenser", "cool-
ing" becomes "heating".
H
C
EATING
YCLE
The heat pump operates in the heating cycle by redirecting refrig-
erant flow through the refrigerant circuit external to the compres-
sor. This is accomplished with through the reversing valve. Hot
discharge vapor from the compressor is directed to the indoor coil
(evaporator on the cooling cycle) where the heat is removed, and
the vapor condenses to liquid. It then goes through the expansion
device to the outdoor coil (condenser on the cooling cycle) where
the liquid is evaporated, and the vapor goes to the compressor.
C O O LIN G
S E RV IC E P O RT
S E RV IC E VA LV E
S E R V IC E P O R T
C O M P R E S S O R
D IS T RIB U TO R
E X P A NS IO N D EV IC E
C H E C K V AL V E
IN DO O R
O R IF ICE
S E R V IC E
C O IL
V A LV E
H E A TIN G
S E R V IC E P O R T
S E R V IC E V A LV E
CO M P R E SS O R
DIS T R IBU TO R
C H E CK V A LV E
IN D O O R
O R IF IC E
S E R V IC E
CO IL
VA LV E
When the solenoid valve coil is operated either from heating to
cooling or vice versa, the piston in the reversing valve to the low
pressure (high pressure) reverse positions in the reversing valve.
The following figures show a schematic of a heat pump on the cool-
ing cycle and the heating cycle. In addition to a reversing valve, a
heat pump is equipped with an expansion device and check valve
for the indoor coil, and similar equipment for the outdoor coil. It is
also provided with a defrost control system.
The expansion devices are flowrator distributors and perform the
same function on the heating cycle as on the cooling cycle. The
flowrator distributors also act as check valves to allow for the re-
verse of refrigerant flow.
When the heat pump is on the heating cycle, the outdoor coil is
functioning as an evaporator. The temperature of the refrigerant in
the outdoor coil must be below the temperature of the outdoor air
in order to extract heat from the air. Thus, the greater the difference
in the outdoor temperature and the outdoor coil temperature, the
greater the heating capacity of the heat pump. This phenomenon
is a characteristic of a heat pump. It is a good practice to provide
9
R E V E RS IN G V A LV E
A C C U M U LA TO R
S E R V IC E PO R T
C H E CK V A LV E
O U TDO O R
O R IF IC E
CO IL
RE V E R S IN G V A L V E
A C CU M U LA TO R
DIS T R IB U TO R
S E RV IC E PO R T
CH E C K VA L V E
O U TDO O R
O R IF IC E
C O IL
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