Carrier PC211 Start-Up, Operation And Maintenance Instructions Manual page 159

Calculate Minimum Load
To calculate minimum load conditions, estimate the temperature difference that the cooler
will have at 10% load, then estimate what the suction and condensing temperatures will be at
this point. Use the proper saturated pressure and temperature for the particular refrigerant
used.
Suction Temperature:
43 F (6.1 C) = 73 psig (503 kPa) saturated refrigerant pressure (HCFC-22)
Condensing Temperature:
70 F (21.1 C) = 121 psig (834 kPa) saturated refrigerant pressure (HCFC-22)
Minimum Load T1:
45.5 – 44 = 1.5° F (7.5 – 6.7 = 0.8° C)
Minimum Load P1:
121 – 73 = 45 psid (834 – 503 = 331 kPad)
Again, to avoid unnecessary surge prevention, add 10 psid (70 kPad) at P1 from these
conditions:
T1 = 1.5 F (0.8 C)
P1 = 60 psid (410 kPad)