ultralo1
05-02-2007, 02:12 PM
Well as you can see I am a newbie here and I hope this is in the right section.
I mostly work on scientific refrigeration, but I have inherited a 20ton water chiller that is used to help keep a MRI magnet cool. It is a dual compressor setup and uses R22. It runs on one compressor until it cannot handle the load then the second kicks in. The water temp that we are trying to maintain is 40F. The second does not come in until water temp is 56F. There are four condensor fans, 2 for each compressor, and they are cycled with the compressor contactors. At the evaporator, shell and tube, they have a Hot gas regulator, set for 58psig, after the TXV. The suction line comes from the evap, through a CPR and back to the comps. The compressors are in parralle to each other, Common suction and discharge lines.
After I inherted it we get a trouble call. I find that the hot gas line has been shut off at the valve behind the hot gas regulator. I turn on the valve and all is good. I talk with the customer and find out that they had to call in a tech at least twice a year, once in spring and once in fall. I went and checked the hotgas regulator and it would not adjust. I told the customer that we would have to change it out. I called the manufacter and he stated that that the system had a design problem and I would need to install a time delayed Normally closed solenoid valve on the hotgas line as to allow head pressure to build up pass the 58psig as to keep the regulator closed. I did all of that. system worked great untill the other day when our outside temp dropped below 15F. I went and checked the system and the regulator was standing open and bypassing the condesor all together, water temp was 60F. I disconnected the solenoid and allowed the valve to close. Everything went back to normal.
So my question is what is causing this unit to go into hot gas bypass and hang there?
Low Charge? site glass is full.
I mostly work on scientific refrigeration, but I have inherited a 20ton water chiller that is used to help keep a MRI magnet cool. It is a dual compressor setup and uses R22. It runs on one compressor until it cannot handle the load then the second kicks in. The water temp that we are trying to maintain is 40F. The second does not come in until water temp is 56F. There are four condensor fans, 2 for each compressor, and they are cycled with the compressor contactors. At the evaporator, shell and tube, they have a Hot gas regulator, set for 58psig, after the TXV. The suction line comes from the evap, through a CPR and back to the comps. The compressors are in parralle to each other, Common suction and discharge lines.
After I inherted it we get a trouble call. I find that the hot gas line has been shut off at the valve behind the hot gas regulator. I turn on the valve and all is good. I talk with the customer and find out that they had to call in a tech at least twice a year, once in spring and once in fall. I went and checked the hotgas regulator and it would not adjust. I told the customer that we would have to change it out. I called the manufacter and he stated that that the system had a design problem and I would need to install a time delayed Normally closed solenoid valve on the hotgas line as to allow head pressure to build up pass the 58psig as to keep the regulator closed. I did all of that. system worked great untill the other day when our outside temp dropped below 15F. I went and checked the system and the regulator was standing open and bypassing the condesor all together, water temp was 60F. I disconnected the solenoid and allowed the valve to close. Everything went back to normal.
So my question is what is causing this unit to go into hot gas bypass and hang there?
Low Charge? site glass is full.