Table of Contents
Advertisement
Compressor
This item is activated by the contactor for heating and cooling,
except 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
termination 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 refrigerant charge or
outdoor conditions are severe (i.e. 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
normally open above their set points and closed below to
permit staging 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. For GPC/GPH models, the motor is energized
directly by the room thermostat for X-13 motors. X-13 motors
are constant torque motors with very low power consumption.
For APH models, the motor is energized by the fan control
board for ECM motors. ECM motors are constant CFM 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).
HEAT PUMP OPERATION
C
C
OOLING
YCLE
When the heat pump is in the cooling cycle, it operates exactly
as a Air Conditioner unit.
H
C
EATING
YCLE
The heat pump operates in the heating cycle by redirecting
refrigerant flow through the refrigerant circuit external to the
compressor. 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.
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 cooling 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 reverse 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 supplementary
heat for all heat pump installations in areas where the
temperature drops below 45°F. It is also a good practice to
provide sufficient supplementary heat to handle the entire
heating requirement should there be a component failure of
the heat pump, such as a compressor, or refrigerant leak, etc.
Since the temperature of the refrigerant in the outdoor coil on
the heating cycle is generally below freezing point, frost forms
on the surfaces of the outdoor coil under certain weather
conditions of temperature and relative humidity. Therefore, it
is necessary to reverse the flow of the refrigerant to provide
hot gas in the outdoor coil to melt the frost accumulation. This
is accomplished by reversing the heat pump to the cooling
cycle. At the same time, the outdoor fan stops to hasten the
temperature rise of the outdoor coil and lessen the time
required for defrosting. The indoor blower continues to run
and the supplementary heaters are energized.
10
Hide quick links:
Advertisement
Table of Contents
