McQuay MDS030A, Service Manual

Page: 49 / 166

Service Manual SM-MDS_(ii) 43

Defrost Finish Temperature : The defrost cycle will stop once TH9 exceed this set point. The lower the
temperature, the faster the defrost cycle will end. The allowable range is from 10°C to 50°C (Default value for
(5)MDS80-240B/BR is 15°C for (5)MDS260-500B/BR is 18°C).

Defrost Interval Time : The interval time between defrost cycle. The smaller the value, the shorter time
between the defrost cycle. The allowable range is from 25 minutes to 90 minutes. Default value is 45 minutes.

Defrost Operation Time : The duration of the defrost cycle. The smaller the value, the short the defrost
duration. The allowable range is from 5 minutes to 15 minutes. Default value is 10 minutes.

Defrost Delay Time : This option is for future provision. Currently is not available.

Sub-cool Circuit Parameter : The next parameter is TscA1, TscA2, TscT1, TscT2, TscT3 which located inside
a same box. These 5 setting is use to change the sub-cool circuit, which is only available in the MDS-B series
outdoor ((5)MDS 80-500 B/BR).
The main mechanism controlling the sub-cool circuit is the EXV 4. TscA1 & TscA2 is the reference temperature
for TH9, which is the refrigerant temperature before sub-cool circuit. TscT1, TscT2 & TscT3 is the Sub-cool target
temperature the system needs to achieve. The actual sub-cool temperature will be based on TH9-TH10.
Example of Sub-Cool Circuit Control (with default value)

Superheat degree : This is the parameter for controlling outdoor superheat (EXV 1). This option is only
applicable for heatpump model and EXV 1 is only used during heating cycle. The EXV 1 will open to achieve
the target set here. Default value will be 5°C for R22 and 3°C for R410A model.
Outdoor super heat (Tsh) = T12 (Suction Temp)
– Te (Saturation temperature)

EXV1, EXV2, EXV3 and EXV4 : This is to manually control the opening of the EXV. It is only applicable for
MDS-B series outdoor ((5)MDS 80-500 B/BR). EXV1/2/3 is only use during heating cycle. It remains shut
during cooling or defrosts cycle. These EXV will not be available in cooling only model. EXV 4 is only use
during cooling cycle and remains shut during heating cycle.
TscA1
TscA2
TH9 (deg C)
Target for Sub - cool temp TscT1 TscT2 TscT3
32 deg C
40 deg C
3 deg C 8 deg C 12 deg C
TscA1
TscA2
TH9 (deg C)
Target for Sub - cool temp TscT1 TscT2 TscT3
32 deg C
40 deg C
3 deg C 8 deg C 12 deg C
As the coil leaving temperature increase, the system will increase the sub-cool temperature
for better performance and long piping application.
4