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Inverter Compressor Heating State Descriptions
The Inverter Compressor Heating State determines the
operation of the following devices:
• Inverter Compressor
• Fixed Speed Compressor (if present)
• Outdoor Fan(s)
• 4 Way Reversing Valve (4WV)
• Outdoor Expansion Valve (EVO)
• Indoor Expansion Valve (EVI)
• Receiver Solenoid Valve (SVR)
• Bypass Solenoid Valve (SVB)
Heating Off
Compressor heating operation begins in the Off state. When in
the Off state, all devices are off or closed. The state remains
here until there is a call for heating.
Pre Start Pressure Equalization
In the Pre Start Pressure Equalization state the SVB valve is
opened to divert hot gas leaving the compressor directly to
the suction line to equalize the pressures in the system before
beginning compressor operation. The outdoor fan is set at 50%
speed. Operation remains in this state for 90 seconds. When in
the Pre Start Pressure Equalization state, all devices are Off or
closed except the outdoor fan(s) and SVB. The outdoor fan(s)
speed is set to 50%.
Initialization
In the Initialization state either the Standard Initialization or
Alternate Initialization sequence is used in order to manage
refrigerant and assure the 4-way valve is switched. The
Alternate Initialization sequence is used the rst time the unit
enters heating after unit power up, or when the compressors
had last operated in cooling, or if it has been a long time since
heating has operated and it is cold outdoors. Otherwise the
Standard Initialization Sequence is used.
Table 66: Standard Initialization Sequence
See page 86 for more information about what is a compressor “step”.
Device Step 1 Step 2 Step 3 Step 4
Inverter Compressor & Comp 3
Inverter Compressor Speed=minimum
Comp 3=Off
Inverter Compressor Speed=Smaller of
Step 12 or Maximum
Comp 3=Off
← A
Inverter Compressor Only Inverter Compressor Speed=minimum
If OAT≤59°F, Inverter Compressor
Speed=Smaller of Step 12 or Maximum
If OAT>59°F, Inverter Compressor
Speed=minimum
← A
Outdoor Fan Outdoor Fan=100% ← ← ←
4 Way Valve (HeatPump) ON ← ← ←
Outdoor Coil Expansion Valve (EVO)
(HeatPump)
EVO=0% ← B ←
SVR (HeatPump) Closed ← ← ←
SVB
Normally Open
Close if either of the following is true:
60 seconds elapses from the beginning of
Step 1
Discharge superheat>18°F
← ← ←
Indoor Coil Expansion Valve (EVI) EVI=100% C ← ←
Time Duration 10 seconds 5 seconds 5 seconds D
A. Inverter compressor speed is increased until the 4-way valve is seated (discharge minus suction pressure >57 psi) and as
long as the suction pressure is above 43 psi and. Comp 3 remains OFF
B. The outdoor expansion valve is controlled to keep the suction superheat between 3.6°F and 9.0°F.
C. Standard Initialization lasts a maximum 120 seconds. It is completed early anywhere between 10 seconds and 120 seconds
if discharge pressure is high (above 384 psi) or when the 4-way valve has been seated for 60 seconds (differential pressure
above 57 psi).
OM 1141-3 • MICROTECH UNIT CONTROLLER 116 www.DaikinApplied.com
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