CO₂ chiller cycling: an EVV body fault case
A CO₂ chiller compressor repeatedly stopped and restarted. The electronic expansion valve (EVV) was seen closing as the compressor stopped, but changing its coil did not resolve the behaviour. Replacing the EVV body was followed by normal operation and improved superheat.
The symptom
During a service investigation, the compressor stopped and later restarted, with no alarm reported. The EVV was observed gradually closing as the compressor stopped. The same behaviour continued after the EVV coil was changed, so the coil change alone had not resolved the fault.
What the readings showed
During one test, the compressor stopped at 18 bar while the EVV display showed about 67% open. These are readings from this particular visit, not target values. Exact superheat readings, a full operating trend and a long post-repair observation were not recorded.
The repair and result
The EVV body was replaced. Ramazan reported that the system then operated normally and that superheat improved. This outcome supported the EVV body as the fault in this case. The available notes do not record the internal failure mechanism or enough post-repair readings to establish a detailed performance baseline.
Why this case is useful
Compressor cycling and a valve appearing to close can have more than one possible explanation. In this case, changing the coil did not fix the problem, while replacing the valve body was followed by an improvement. A symptom by itself does not prove low refrigerant charge, a faulty coil or a failed valve body. Diagnosis should follow the system's measured operation and the manufacturer's service procedure.
The service notes also record that 200 g of CO₂ was added earlier in the troubleshooting. That is part of this individual visit, not a general recommendation or proof that adding refrigerant is the right response to compressor cycling. Refrigerant work must be based on an appropriate diagnosis and carried out by a qualified refrigeration technician.
What to record on a similar call
- Whether the compressor is stopping, restarting or remaining off, and whether an alarm is present.
- What the controller reports for valve position and what the valve/system is observed to do.
- Operating pressures, temperatures and superheat over time, with units and test conditions.
- What was changed and whether the same symptom remained afterward.
- How long the system was observed after repair and whether operation stayed stable.
Safety
CO₂ refrigeration systems operate at high pressures. Do not open, adjust or service the refrigeration circuit unless you are qualified and following the equipment manufacturer's procedures. If a system is cycling or not holding temperature, record the alarm and displayed readings and contact a refrigeration engineer.