Service Manual SM-MDS_(ii) 47
5.3 Add in additional refrigerant
Even though the MDS outdoor unit is pre-charged with refrigerant from the factory, but additional refrigerant is
still required. This is because the pre-charge of refrigerant from the factory may not be sufficient to ensure the
whole system to work according to design condition due to different piping length. There are two ways to obtain
the additional refrigerant required. It can be obtain from the report generated by selection software or through
manual calculation. Whichever method user used to determine the additional refrigerant, it is recommended to
monitor the parameter of the outdoor model to ensure that the unit is working properly. The calculation done is
only served as a guideline.
Report from
Selection Software
After using the Selection Software to choose the appropriate model and piping layout,
user is allowed to generate the information into a report. From the report itself, the
proposed additional amount of refrigerant required are stated in the report.
Additional charge required
To use this method, the user is required to get the whole piping schematic diagram.
After that, user will need to know the exact pipe length and their respective diameter.
Then, user will need to sum up the piping length used on the liquid pipe only base on
different diameter. Once the piping length of different diameter is obtained, apply the
length into the formula below to calculate additional refrigerant required.
Additional charge amount:
= ∑ Li* Gi
Example
= (Piping Length for 15.88mm X Additional Charge Amount)
+ (Piping Length for 12.7mm X Additional Charge Amount)
+ (Piping Length for 9.52mm X Additional Charge Amount)
+ (Piping Length for 6.35mm X Additional Charge Amount)
Caution that, the additional charge amount of different pipe diameter varies base on
type of refrigerant.
Pipe Diamater (mm) 6.35 9.52 12.70 15.88 19.05
R22 Additional Charge (g/m) 50 80 120 180 290
Pipe Diamater (mm) 6.35 9.52 12.70 15.88 19.05
R41A additional Charge (g/m) 45 70 120 180 260
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