10 Service Manual SM-MDS_(ii)
2.2 MDS Indoor System and Control
Indoor coil sensors’ location and naming for cooling (left) and heating (right)
The indoor unit for MDS system is slightly different with indoor unit of ordinary split system.
For MDS indoor, there are additional sensors which allow precision control over
temperature.
The modulation of indoor EXV is controlled by the readings of T
in
and T
out
of the indoor unit.
Generally, the opening/modulation of indoor EXV is described by the number of steps,
where each step refers to different EXV opening size. For example, if the indoor unit
requires more cooling, the EXV steps will increase to allow more refrigerant to flow into the
indoor.
The table above shows the fan speed modulation when indoor fan speed is set to AUTO. It
is applicable for both cooling and heating cycle. For heating mode, readings from sensor
T
mid
is used to control the fan speed.
This protection is available during cooling and dry operation. Anti-freeze protection will
activates when T
mid
is ≤ -2ºC for 2 minutes. When anti-freeze protection activates, all EXV
valve will close. Indoor anti-freeze will end when T
mid
is ≥ 15ºC. All indoor unit will resume
operation (EXV valve open) when this condition is achieved.
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