Heat Pump
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OM 1263 • MICROTECH UNIT CONTROLLER
Heat Pump
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 first 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 41: Standard Initialization Sequence, 3–15 Tons
Device
Step 1
Step 2
Step 3
Step 4
Inverter Compressor & Comp3
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 ≤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 (Heat Pump)
ON
←
←
←
Outdoor Coil
Expansion Valve (EVO)
(Heat Pump only)
EVO = 0%
←
←
←
SVR (Heat Pump only)
Closed
←
←
←
SVB
Size ≠ 15 tons:
Normallly Open
Close if either of the following is true:
60 seconds elapses from the
beginning of Step 1
Discharge superheat > 18°F
←
Size = 15 Tons
Normallly 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
D = 15 Ton size
C
5 Seconds ≠ 15 Ton size
A . Inverter compressor speed is increaded until the 4-way valve is seated (discharge minus suciton pressure >57 psi) and as
long as the discharge pressure is less than 221 psi . Comp3 is always 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 (fin) temperature >167°F.
C . The indoor expansion valve is controlled to keep the suction superheat between 3 .6°F and 9 .0°F .
D .
Step 3 ends when either minimum Step 16 reached, differential pressure is greater than 26 psi for 3 seconds, or the stage
has been active for 3 minutes .
See page 50 for
more information about what is a compressor
“step”.
Summary of Contents for MicroTech III DPS
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