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Heat pumps are also equipped with an Electronic
Expansion Valve (EEV) which will be set to the "Check
Valve Position" and drive wide open. The EEV does not
provide refrigeration control in the cooling mode of
operation.
H H e e a a t t P P u u m m p p H H e e a a t t i i n n g g M M o o d d e e o o f f O O p p e e r r a a t t i i o o n n
When a request for heating capacity is sent from the
communicating comfort control to the outdoor unit, the
Drive will respond by flashing the STATUS LED two
times per second and the CDA will display HEATING in
the SYSTEM STATUS home screen.
In the heating mode of operation the LSOV solenoid
will be pulsed to position the valve for heating at the
start of each call for capacity.
During heating mode, the EEV will be in the controlling
state. Refrigerant flow is managed by incrementally
opening or closing the valve to control compressor
superheat under a wide range of conditions. Superheat
is calculated with feedback to the Drive from a suction
line temperature sensor and a suction line pressure
transducer. The Drive will target 10 degrees (+/-2) of
superheat and drive a valve position by periodically
pulsing the stepper motor and then monitoring
compressor superheat results. Control signals to the
EEV stepper motor are 12 volt DC pulses from J5 on the
Drive. The EEV step position and compressor
superheat can be monitored through the CDA monitor
menu during runtime operation. The Drive will close
the EEV with every OFF cycle and drive the valve to
wide open during defrost or cooling mode of
operation.
N N o o t t e e : : When a heat pump system is first powered up,
the EEV produces an audible sound (soft
ratcheting sound) as the valve drives to the
closed position.
D D e e f f r r o o s s t t M M o o d d e e f f r r o o m m C C y y c c l l i i n n g g - - S S t t a a g g e e
When the system is operating in cycling-stage and the
control initiates a Defrost, the indoor control
simultaneously:
•
De-energizes the outdoor fan motor,
•
Drives the OD EEV to full open and,
•
Commands the SOV to change to the cooling mode.
There is a brief switchover time-delay (to allow
refrigerant pressures to stabilize) before the
compressor is commanded to run at Maximum Speed
Cooling to perform Defrost.
The outdoor control also sends a demand message to
the indoor unit to run the blower at Maximum Speed
Cooling and energize auxiliary heat (if equipped).
Auxiliary heat blower speed may be higher than
Maximum Speed Cooling and will take precedence
during defrost.
The Defrost Mode will be terminated after the OD coil
temperature reaches 47° For the maximum time
4TWL9048A-SF-1C-EN
override of 15 minutes has lapsed. At Defrost
termination, the compressor will be commanded to go
to the Defrost Switchover Speed. After that speed is
achieved, the SOV position will be changed back to the
heating mode of operation and the OD fan will be
turned back on. Following the refrigerant stabilizing
delay, the compressor will be allowed to run at any
speed commanded by thermostat demand.
The outdoor control will send the necessary pulse
signals to the stepper motor coil returning the EEV to a
controlling position that matches capacity demand and
begin monitoring superheat.
D D e e f f r r o o s s t t M M o o d d e e f f r r o o m m M M o o d d u u l l a a t t i i n n g g - - S S t t a a g g e e
When the system is operating in modulating-stage and
the control initiates a Defrost, the outdoor control
commands the compressor to go to the Defrost
Switchover Speed.
After the lower speed is achieved, the SOV will be
switched into the cooling mode and the control will
simultaneously de-energize the RPM signal to the
outdoor fan motor and drive the OD EEV to full open.
There is a brief switchover time-delay (to allow
refrigerant pressures to stabilize) before the
compressor is commanded to run at Maximum Speed
Cooling to perform Defrost.
The outdoor control also sends a demand message to
the indoor unit to run the blower at Maximum Speed
Cooling and energize auxiliary heat (if equipped).
Auxiliary heat blower speed may be higher than
Maximum Speed Cooling and will take precedence
during defrost.
The CDA will show DEFROST in the Home Screen.
The Defrost Mode will be terminated after the OD coil
temperature reaches 47°F or the maximum time
override of 15 minutes has lapsed. At Defrost
termination, the compressor will be commanded to go
to the Defrost Switchover Speed. After that speed is
achieved, the SOV position will be changed back to the
heating mode of operation and the OD fan will be
turned back on. Following the refrigerant stabilizing
delay, the compressor will be allowed to run at any
speed commanded by thermostat demand.
The outdoor control will also send the necessary pulse
signals to the stepper motor coil returning the EEV to a
controlling position that matches capacity demand and
begin monitoring superheat.
The system will stay in the Defrost, Maximum Speed
Cooling even if the comfort control demand changes
from modulating-stage to cycling-stage. However, the
system will shut down if the comfort control demand
message for cycling-stage capacity ends. The system
will continue the current defrost cycle the next time the
comfort control sends a demand message for
compressor heat.
S S e e q q u u e e n n c c e e o o f f O O p p e e r r a a t t i i o o n n
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