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5. Set the thermostat at the appropriate setting for cooling
and heating or automatic changeover for normal use.
6. Be sure the Owner is instructed on the unit operation,
filter, servicing, correct thermostat operation, etc.
The foregoing
=Start-up Procedure
and Check List" is recom-
mended to serve as an indication that the unit will operate nor-
mally.
COMPONENTS
Contactor
This control is activated (closed) by the room thermostat for both
heating and cooling. The contactor has a 24V coil and supplies
power to the compressor and outdoor fan motor.
Crankcase Heater
This item is "ON" whenever power is supplied to the unit. It warms
the compressor crankcase thereby preventing liquid migration and
subsequent compressor damage. The insert type heater is self regu-
lating. It is connected electrically to the contactor L1 and L2 termi-
nals.
Condenser Motor
This item is activated by the contactor during heating and cooling,
except during defrost and emergency heat operation. On 460V
heat pumps, the condenser motor is activated by the CMR.
Compressor
This item is activated by the contactor for heating and cooling, ex-
cept during emergency heat. It is protected by an internal overload.
Contactor Relay
This control is activated by the thermostat (24V coil) and supplies
power to the contactor.
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 De-
frost cycle will take only 2-3 minutes unless system is low on charge
or outdoor conditions are severe. (windy and cold)
Outdoor Thermostat
These optional controls are used to prevent full electric heater op-
eration 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, ttthe outdoor ambient
temperature is below 0° F (-18 ° C) with 50% or higher RH, an out-
door 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 X-13 motors (4 or 5 Ten
units). X-13 motors are constant torque motors with very low power
consumption. This motor is energized by a 24V signal from the
thermostat. (See Air F/ow Measurement and Adjustment for speed
adjustment instructions). 460V 3-phase blower motors are driven
by EMR.
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
COOLING
CYCLE
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".
HEATING
CYCLE
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.
COOLING
SERVICE
PORT
REVERSING
VALVE
OE°V,CE
.
/
o , Ol
l
1
T
C.EC:VALVE
T
IN[3OOR
ORIFICE
SERVICE
ORIFICE
OUTDOOR
COIL
VALVE
COIL
HEATING
SERVICE
PORT
--
SERVICE
VALVE
/
t
INDOOR
COIL
AEVEASING
VALVE
/
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.
9
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