Trane CVHE Troubleshooting Manual page 99

Evaporator Refrigerant Temperature Limit
The Evaporator Refrigerant Temperature Limit is a multistage control that acts to prevent chiller
shutdown when the evaporator refrigerant temperature approaches the cutout setpoint by
reducing chiller capacity. Chiller capacity is reduced by the following steps, providing increasingly
aggressive action as the trip point is approached:
1 Limit requests for capacity increases.
2 Prohibit requests for capacity increases.
3 Initiate stepped capacity reduction.
4 Initiate maximum capacity reduction.
The purpose of this limit is to provide maximum capacity while preventing chiller shutdown due to
low evaporator refrigerant temperatures.
ERR3 = Temperature error Deg F
220.0*(Err3 + 0.5); CTV Only
60.0*(Err3 + 0.5); RTHB Only
5.0*(Err3 ); ABS Only
The Low Refrigerant Temperature Cutout setpoint is found in the Field Startup menu.
Design:
Lowest standard chilled water setpoint (CWS) = 37°F
Lowest standard low refrig. temp. cutout (LRTC) = 28.5°F
Lowest standard refrig. temp. limit setpoint (LRTLS) (28.5 + 2) = 30.5°F
Minimum differential between LRTC and CWS = 6.0°F
CVHE-SB-32A
Forced
Unload
Hold
DS3 (#steps)
-0.5
Limit
Loading
0.5
3; CTV Only
7; RTHB Only
2; ABS Only
No
Limit
1250
100.0*(Err3 - 0.5); CTV Only
30.0*(Err3 - 0.5); RTHB Only
3.0*(Err3 - 0.5); ABS Only
94