Hi

I have a ~8yr old Trane ERTHA300 (rotary screw chiller) used for mall air-conditioning in South East Asia. (ambient: 30C, 90%RH)

It has been running fine for at least the past 3 years, but recently, it is always tripping after about 15-30 minutes of running:

starts with status A74 (normal running),
15 minutes later status changes to A77 "Run: evaporator limit(3)"
3 minutes later it trips on status bFb "Low evaporator refrigerant temp"

Water temperatures in and out of the evaporator and condenser seem normal.
Evap water in/out: 11-13C / 7-8C
Cond water in/out: 27-30C / 31-34C

Any ideas?

Some possibilities I've thought of:
  • dirty evaporator heat exchange tubes causing large approach
  • bad thermistor under-reporting evap refrigerant temp