Hi everyone,

I’m looking for some assistance with a 26-ton CGAM chiller. We acquired this customer about a month ago, and I’ve been chasing an issue that has me stumped.

The original complaint was that the chiller would not run because the flow switch would not prove. According to the customer, the chiller was installed about seven years ago. It operated well for the first two years, but after that they began having ongoing issues. Unfortunately, they couldn’t tell me exactly what those issues were. About three years ago they gave up on the chiller altogether and installed window units throughout the apartments it serves.

Our first finding was that the pump impeller was badly damaged and the water strainer was clogged. We have replaced the water pump and cleaned the strainer.

Once proper water flow was established, we found the refrigerant charge was low due to a leak in the discharge line. We recovered the remaining refrigerant, repaired the leak, evacuated the circuit, and charged it with 18 lbs of new R-410A as a starting point. The factory charge is 20 lbs.

After starting the chiller, I noticed there was essentially no subcooling and the superheat was slightly high. I added the remaining 2 lbs to bring it to the factory charge and watched it operate. Shortly afterward, the chiller tripped on a “Loss of Charge” alarm.

From what I’ve been able to find, this alarm can occur if the EXV opens beyond its expected operating range. This unit has two single-stage compressors. With one compressor running, the EXV would frequently open to around 60% or more before eventually tripping on Loss of Charge.

Since my subcooling was still at 0°F, I decided to add additional refrigerant. I added another 6 lbs, which increased my subcooling to approximately 5°F with one compressor running, but it still dropped to 0°F with both compressors operating. The EXV opening improved somewhat, operating around 43% with one compressor and about 73% with both compressors running.

At that point I decided to leave it alone and continue monitoring. The chiller actually ran the entire day without issue until about 10:00 PM, when it once again tripped on a Loss of Charge alarm.

The following day I returned and added another 3 lbs. That brought my subcooling up to 10°F with one compressor running and 5°F with both compressors running. The problem is that I’m now about 9 lbs over the factory charge, yet the IOM indicates I should have 10-12°F of subcooling with both compressors operating.

After leaving the site, the customer called to let us know it shut down again.

At this point I’m stumped. I’ve triple-checked the accuracy of all pressure transducers and thermistors, and they are reading correctly. I’ve also verified that the EXV is responding properly and is capable of opening and closing.

I don’t work on many Trane chillers, and this is the first time I’ve encountered a chiller that generates a Loss of Charge alarm based primarily on EXV position. I’ve also searched for a way to adjust the sensitivity of the alarm or disable it temporarily for troubleshooting, but I haven’t found anything.

Has anyone run into this before or have any suggestions on what else I should be looking at? I’d really appreciate any insight. Thanks in advance, and I’ll continue researching it on my end as well.