H4nkj
Chemical
- Jun 29, 2022
- 4
Please bear with me if I am not using some of these HVAC terms correctly. I have a bit of refrigerant knowledge but the refrigerant cycle has always been tertiary to my work.
I have four air-cooled glycol/water chillers purchased from an OEM. The refrigerant circuit is equipped with a semi-hermetic compressor. There is a solenoid on the liquid line and before the hot gas by-pass valve. When the glycol temperature drops below set point, the controller puts the system in an unloaded cycle. This opens the cylinder solenoid in the compressor, opens the hot gas by-pass solenoid and closes the liquid line solenoid. As the glycol temperature creeps up, the system goes back into cooling mode by closing the solenoid in the compressor, closes the hot gas by-pass solenoid, and opens the liquid line solenoid. When this happens, the low side refrigerant pressure drops very low (< 5 psig) and it is tripping out one of the units. All of them appear to be dropping low in pressure, but only one is actually tripping on low refrigerant pressure. The only help the OEM provided was telling me to change the setpoint of the low refrigerant switch. That did not fix the problem.
I suspect that the controller may be closing the hot gas by-pass a split second before opening the liquid line solenoid, thus causing a brief no-flow situation and causing the pressure to drop. I had a third-party HVAC technician out. He explained to me that you do not typically close the liquid line solenoid during the unloading phase. He held the liquid line solenoid open through the unloading and cooling cycles. The system seemed to operate just fine and did not trip out.
So my question is, what is the typical function of the liquid line solenoid? Is my third-party HVAC technician correct in saying that valve should not be closed during the unloading? Or did the OEM get the design right and I should focus on changing the valve sequence?
I have four air-cooled glycol/water chillers purchased from an OEM. The refrigerant circuit is equipped with a semi-hermetic compressor. There is a solenoid on the liquid line and before the hot gas by-pass valve. When the glycol temperature drops below set point, the controller puts the system in an unloaded cycle. This opens the cylinder solenoid in the compressor, opens the hot gas by-pass solenoid and closes the liquid line solenoid. As the glycol temperature creeps up, the system goes back into cooling mode by closing the solenoid in the compressor, closes the hot gas by-pass solenoid, and opens the liquid line solenoid. When this happens, the low side refrigerant pressure drops very low (< 5 psig) and it is tripping out one of the units. All of them appear to be dropping low in pressure, but only one is actually tripping on low refrigerant pressure. The only help the OEM provided was telling me to change the setpoint of the low refrigerant switch. That did not fix the problem.
I suspect that the controller may be closing the hot gas by-pass a split second before opening the liquid line solenoid, thus causing a brief no-flow situation and causing the pressure to drop. I had a third-party HVAC technician out. He explained to me that you do not typically close the liquid line solenoid during the unloading phase. He held the liquid line solenoid open through the unloading and cooling cycles. The system seemed to operate just fine and did not trip out.
So my question is, what is the typical function of the liquid line solenoid? Is my third-party HVAC technician correct in saying that valve should not be closed during the unloading? Or did the OEM get the design right and I should focus on changing the valve sequence?