29
Do not use the compressor for pressurizing the system to check the pressostat
limits.
The high pressure and low pressure cut-out eventually used should have a manual reset feature for the
highest level of system protection.
Ensure that the discharge gas temperature is always higher than the saturation
temperature (including during compressor start after long stop and defrost).
8.13 DISCHARGE LINE THERMOSTAT
Table
8.12 12 Discharge gas maximum pressures/temperature
REFRIGERANT
APPLICATION
PULL-DOWN MAXIMUM PEAK
MAXIMUM
DISCHARGE GAS
TEMPERATURE
CONDITIONS
(°C)
MPA (rel)
BAR (rel)
AT CONDENSING
TEMPERATURE (°C)
R404A
LBP
2.77
27.7
60
125
R452A
2.72
27.2
60
125
R449A
2.60
26.0
60
125
R448A
R404A
MBP
3.10
31.0
65
125
R452A
3.06
30.6
65
125
R449A
2.92
29.2
65
125
R448A
R134A
2.26
22.6
75
125
R513A
2.22
22.2
75
125
IMPORTANT
IMPORTANT
8.13.1 DISCHARGE LINE THERMOSTAT FOR LBP
8.13.2 DISCHARGE LINE THERMOSTAT FOR MBP
A discharge line thermostat can be required in the compressor control circuit. The thermostat has a cut out
setting that will insure discharge line temperatures below the 125°C maximum limit. It should be installed
approximately 160 mm from the discharge tube outlet. If a service valve is installed at the discharge tube, the
thermostat should be located 130 mm from the valve braze. For proper operation in extremely low outdoor
ambient conditions, it is recommended to insulate the thermostat to protect it against a direct air stream.
Operation above, or on the left side of the operation envelope can cause high compression ratio or excessive
internal compressor temperatures. This will result in overheating of the involutes, causing excessive wear resulting
in premature compressor failure. If the system design can’t guarantee to operate inside the operation envelope,
then the discharge line thermostat is required in the compressor control circuit. The suggested highest cut out
setting for the discharge line thermostat is 125°C; it should be installed approximately 170 mm from the discharge
tube outlet, or approximately 130 mm from the valve outlet port.
