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Outdoor Frequency Control; Electronic Expansion Valve (Eev) Control; Valve Adjustments Due To Hot Gas Discharge Temperature Limits; 4-Way Valve Control During Heating Mode - Haier 2U18MS2VHB Service Manual

Ductless multi-split heat pump, outdoor/indoor, wall mount - highwall, 2'x2' compact cassette, 3'x3' large cassette, slim duct, mid-static ducted, medium static ducted, console
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Outdoor Frequency Control

A. The compressor running frequency is range is 20-95 RPS.

Electronic Expansion Valve (EEV) Control

A: EEV SPECIFICATION: Maximum open angle is 500 pulses.
Driving speed is PPS.
B: Start-up EEV Conditional state
When the system is in the Cool/Dry mode, the standard open
angle of the EEV will be set at a position that is determined
by the temperature of the outdoor air. When the outdoor air
temperature is greater than 68°F, the initial setting of the EEV
will be 250 pulse open. If the outdoor air temperature is less
than 68°F, the EEV will open 210 pulses.
In Heating mode, the standard open position will be 250
pulses when the ambient air temperature outdoors is greater
than 50°F. If the air temperature outdoors is less than 50°F,
the open pulse rate is set to 210.
During running operation, the EEV position may be adjusted if
the compressor discharge gas temperature indicates a need
to supply more or less refrigerant to the evaporator circuit.
Here are the control responses and EEV positional changes
that can occur due to either hot or cool discharge gas
Valve Adjustments Due To Hot Gas Discharge
Temperature Limits
If the discharge gas temperature rises above 212°F, the EEV
will open to its widest allowed position to try and reduce the
temperature of the compressor.
If the discharge temperature is greater than 194°F, but less
than 212°F, the EEV will not be adjusted.
If the discharge line temperature drops below 194°F, the EEV
will reduce its size to reduce refrigerant flow.

4-Way Valve Control During Heating Mode

If the 4 way valve fails to switch the hot gas flow to the indoor
coil during a call for heat, the system will enter a protection
routine. If the indoor coil average temperature is below 59°F,
10 minutes after the compressor has started, and stays there
for at least 1 minute, the system will lock out and display a
4-way valve protection fault error code.

Crankcase Heater Control

The crankcase heater is controlled by the ECU. The heater
keeps the compressor oil warm to prevent liquid refrigerant
from migrating to the oil during periods where the system is
not running. The heater will operate during off cycle periods
when the outdoor air temperature is below 80.6°F. When the
outdoor air temperature is greater than 90°F, the heater will
not be energized. When the compressor is running, the heater
will not be energized.

On Demand Defrost Logic

The system defrost function during heat mode is a demand
type system. Two temperatures are monitored by the ECU
to determine if defrosting is needed, they are Outdoor air
temperature Sensor Ta and Outdoor coil temperature Sensor
To enter a defrost cycle on demand, the system must be in
heat mode and the compressor must have run for 10 minutes
continuously and 45 minutes of compressor run time in heat
mode must have accumulated. If the following conditions
have been met for at least 5 continuous minutes, the system
will enter a demand defrost cycle:
Sensor Te must sense a temperature that is less than or equal
Te< CxTa-a
C is calculated as follows:
If Ta < 32°F then C=.8
a is set by SW5-2 switch Factory setpoint is 8
Opposite Switch setting is 6
If the system is in an area that is easy to frost, it is
recommended to set the SW5-2 switch to opposite setting
and change the value of a to 6.
Example: Te = 26°F
Solution: 26°F
27.2°F so the system defrost cycle starts.
The system can only remain in defrost for up to 10 continuous
minutes of run time. The defrost cycle will terminate if sensor
Te reaches 44.6°F for a period of 60 seconds or 53.6°F for a
period of 30 seconds. In either case, the defrost cycle will
terminate after 10 minutes.
If Ta> 32°F then C=.6
Ta = 44°F
44 x .8= 35.2-8=27.2
26°F is colder than
a = 8

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