Midea MHF-18HWN1-Q, Service Manual

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Insulation Work
Installation 101
4 Leakage test: After the vacuum degree reaches -755mmHg, stop vacuum drying and keep the pressure
for 1 hour. If the indicator of vacuum gauge does not go up, it is qualified. If going up, it indicates that
there is moisture or leak source.
8. Additional refrigerant charge
 After the vacuum drying process is carried out, the additional refrigerant charge process need to be
performed.
 The outdoor unit is factory charged with refrigerant. The additional refrigerant charge volume is decided
by the diameter and length of the liquid pipe between indoor and outdoor unit. Refer the following
formula to calculate the charge volume.
Diameter of liquid pipe (mm) Φ 6.35 Φ 9.52 Φ 12.7
Formula V=11g/m×(L-5) V=30g/m×(L-5) V=60g/m×(L-5)
V:
Additional refrigerant charge volume (g).
L :
The length of the liquid pipe (m).
Note:

Refrigerant may only be charged after performed the vacuum drying process.
 Always use gloves and glasses to protect your hands and eyes during the charge work.
 Use electronic scale or fluid infusion apparatus to weight refrigerant to be recharged. Be sure to avoid
extra refrigerant charged, it may cause liquid hammer of the compressor or protections.
 Use supplementing flexible pipe to connect refrigerant cylinder, pressure gauge and outdoor unit. And
The refrigerant should be charged in liquid state. Before recharging, The air in the flexible pipe and
manifold gauge should be exhausted.
 After finished refrigerant recharge process, check whether there is refrigerant leakage at the connection
joint part.(Using gas leakage detector or soap water to detect).
9. Engineering of insulation
9.1 Insulation of refrigerant pipe
9.1.1 Operational procedure of refrigerant pipe insulation
Cut the suitable pipe → insulation (except joint section) → flare the pipe → piping layout and connection →
vacuum drying → insulate the joint parts
9.1.2 Purpose of refrigerant pipe insulation

During operation, temperature of gas pipe and liquid pipe shall be over-heating or over-cooling
extremely. Therefore, it is necessary to carry out insulation; otherwise it shall debase the performance
of unit and burn compressor.
 Gas pipe temperature is very low during cooling. If insulation is not enough, it shall form dew and cause
leakage.
 Temperature of gas pipe is very high (generally 50-100
℃
) during heating. Insulation work must be
carried out to prevent hurt by carelessness touching.
9.1.3 Insulation material selection for refrigerant pipe
 The burning performance should over 120 ℃
 According to the local law to choose insulation materials
 The thickness of insulation layer shall be above 10mm.If in hot or wet environment place, the layer of
insulation should be thicker accordingly.
9.1.4 Installation highlights of insulation construction
 Gas pipe and liquid pipe shall be insulated separately, if the gas pipe and liquid pipe were insulated
together; it will decrease the performance of air conditioner.