Inverter Compressor Cooling State
Descriptions
The Inverter Compressor Cooling State determines the
operation of the following devices:
• Inverter Compressor
• Fixed Speed Compressor (if present)
• Outdoor Fan(s)
• 4 Way Reversing Valve (4WV) (Heat Pump only)
• Outdoor Expansion Valve (EVO) (Heat Pump only)
• Indoor Expansion Valve (EVI)
• Receiver Solenoid Valve (SVR) (Heat Pump only)
• Bypass Solenoid Valve (SVB)
Cooling Off
Compressor cooling operation begins in the Cooling Off state.
All devices are Off or closed. The state remains Off until there
is a call for cooling or dehumidication
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. Operation remains in
this state for 30 seconds [adjustable.] When in the Pre Start
Pressure Equalization state, all devices are off or closed,
except the Outdoor Fan and SVB. The Outdoor fan 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 to assure a 4-way valve is switched.
The Alternate Initialization sequence is used on inverter
compressor units the rst time the unit enters cooling after unit
power up, the compressors had last operated in heating, or if it
has been a long time since cooling has operated and it is cold
outdoors.
Otherwise the Standard Initialization Sequence is normally used.
Table 61: Standard Initialization Sequence
Device Step 1 Step 2 Step 3 Step 4
Inverter Compressor & Comp 3
Inverter Compressor Speed= Minimum
Comp3=Off
Inverter Compressor Speed=Smaller of Step 12 or Maximum
Comp3=Off
← A
Inverter Compressor Only Inverter Compressor Speed= Minimum
If OAT≥50°F or RAT≥73°F, Inverter Compressor
Speed=Smaller of Step 12 or Maximum
If OAT<50°F & RAT<73°F, Inverter Compressor Speed=
Minimum
← A
Outdoor Fan
Outdoor Fan=0% if OAT<68°F
Outdoor Fan=50% if OAT≥68°F
B ← ←
4 Way Valve (Heat Pump) OFF ← ← ←
Outdoor Coil
Expansion Valve (EVO)
(Heat Pump only)
EVO=100% ← ← ←
SVR (Heat Pump only) Closed ← ← ←
SVB
Normally Open
Close if either of the following is true:
60 seconds elapses from the beginning
of Step 1
Discharge superheat>9°F
← ← ←
Indoor Coil
Expansion Valve (EVI)
EVI= 0% 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. Comp 3 remains OFF
B. Outdoor fan capacity is controlled to maintain the discharge pressure between 256 psi and 313 psi. Outdoor fan capacity is
set to 100% if discharge pressure is above 384 psi. Outdoor fan capacity runs at least at minimum capacity if inverter board
(n) temperature >167°F
C. The indoor expansion valve is controlled to keep the suction superheat between 3.6°F and 9.0°F.
D. Standard Initialization lasts a maximum 140 seconds. It is completed early anywhere between 20 seconds and 140 seconds
if the saturated suction temperature is high (above 118°F), the suction pressure is low (below 79 psi) or once the 4-way
valve is seated (differential pressure above 57 psi, suction pressure below 142 psi and suction or discharge superheat
above 27°F).
operator’s guIde
www.DaikinApplied.com 87 OM 1141-3 • MICROTECH UNIT CONTROLLER
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