flamer_the_spar
10-06-2010, 08:31 PM
Hi All.
I was called to a York AHU yesterday. It has a cooling system (2 Ckts, 2 Compressor each ckt, 4 Compressor total), gas WAH and the AHU fan assy, all bolted together to form one cabinet.
Unit would start up and run for about four minutes then shut down. When running the refrigerant stream through the site glass was poor. ID Plate calls for an 8.1 Kg charge of R407C per ckt. I recovered the refrigerant and removed 3.4Kg from Ckt 1 and about 6.5Kg from Ckt 2.
Proceeeded to re-gas and managed to get 4Kg into the circuit unaided, then ran up Ckt 1 and used the compressor to charge the system.
The unit ran for much longer this time but after about ten minutes, the unit shut down.
I studdied the wiring diagram and found there to be a HP and LP sensor wired in series, also running through a device called FS1 and FS2 for the two circuits.
I metered the safety circuit and it was open circuit. Unit would not power back up for about ten minutes.
I found the pressure switches fairly easily and eventually found FS1 and FS2, which were cable tied to the back end of the pipe about 2M from the end of the evaporator coil, close to the HP and LP switches and covered in armourflex tape.
FS1 and FS2 both went open circuit.
I took FS1 and FS2 off the pipes to let the system run up so I could continue to charge the unit up to the 8.1Kg per circuit. It got there with both circuits and the unit has ran perfectly all afternoon.
We will be on site for a few days working on some City Multi kit so will keep an eye on it.
I have ordered 2 new FS temp devices today and will install them early next week.
I fear that the FS1 and FS2 will be ok. I think that they monitor the temp of the pipe and are going open circuit as it is probably to cold.
The charge seems ok, the compressors began to run sweet sounding at about 7.75Kg and there is a good liquid stream through the site glass with very occasional bubbling.
According to the various commissioning paperwork from the last 8 years, the suction pressure is around 3.8 Bar and the discharge is around 14 Bar.
I am getting about 2.7 Bar on the suction and around 12 Bar discharge, tied in each side of the compressors.
We also removed a wasp nest from the pre-filter section and steam cleaned the filters out as I don't think they had been cleaned for a good while. I could not see through them anyhows so a good clean was due. We also cleaned up all the coils.
There is also some minor frosting on the coil (this may be from the steam clean to the filters) and there is various frosting to the TEV's and about ten pipes leaving the TEV to each of the evaporator coil loops.
Frosting had stated to ease off on the coil later on this afternoon, but with a generous coating of frost on the bottom end of the TEV and the feeder copper lines.
If the issue continues, what would be the best way to attack this?
I think I may need to ease off the TEV's and just slightly reduce the flow through the evaporator so the FS1 and FS2 does not activate, so I need the TEV to raise the temp within the evaporator.
The issue suddenly started happening on Friday last week. Unit was running fine until then.
Any help or ideas would be greatly appreciated.
Phil.
I was called to a York AHU yesterday. It has a cooling system (2 Ckts, 2 Compressor each ckt, 4 Compressor total), gas WAH and the AHU fan assy, all bolted together to form one cabinet.
Unit would start up and run for about four minutes then shut down. When running the refrigerant stream through the site glass was poor. ID Plate calls for an 8.1 Kg charge of R407C per ckt. I recovered the refrigerant and removed 3.4Kg from Ckt 1 and about 6.5Kg from Ckt 2.
Proceeeded to re-gas and managed to get 4Kg into the circuit unaided, then ran up Ckt 1 and used the compressor to charge the system.
The unit ran for much longer this time but after about ten minutes, the unit shut down.
I studdied the wiring diagram and found there to be a HP and LP sensor wired in series, also running through a device called FS1 and FS2 for the two circuits.
I metered the safety circuit and it was open circuit. Unit would not power back up for about ten minutes.
I found the pressure switches fairly easily and eventually found FS1 and FS2, which were cable tied to the back end of the pipe about 2M from the end of the evaporator coil, close to the HP and LP switches and covered in armourflex tape.
FS1 and FS2 both went open circuit.
I took FS1 and FS2 off the pipes to let the system run up so I could continue to charge the unit up to the 8.1Kg per circuit. It got there with both circuits and the unit has ran perfectly all afternoon.
We will be on site for a few days working on some City Multi kit so will keep an eye on it.
I have ordered 2 new FS temp devices today and will install them early next week.
I fear that the FS1 and FS2 will be ok. I think that they monitor the temp of the pipe and are going open circuit as it is probably to cold.
The charge seems ok, the compressors began to run sweet sounding at about 7.75Kg and there is a good liquid stream through the site glass with very occasional bubbling.
According to the various commissioning paperwork from the last 8 years, the suction pressure is around 3.8 Bar and the discharge is around 14 Bar.
I am getting about 2.7 Bar on the suction and around 12 Bar discharge, tied in each side of the compressors.
We also removed a wasp nest from the pre-filter section and steam cleaned the filters out as I don't think they had been cleaned for a good while. I could not see through them anyhows so a good clean was due. We also cleaned up all the coils.
There is also some minor frosting on the coil (this may be from the steam clean to the filters) and there is various frosting to the TEV's and about ten pipes leaving the TEV to each of the evaporator coil loops.
Frosting had stated to ease off on the coil later on this afternoon, but with a generous coating of frost on the bottom end of the TEV and the feeder copper lines.
If the issue continues, what would be the best way to attack this?
I think I may need to ease off the TEV's and just slightly reduce the flow through the evaporator so the FS1 and FS2 does not activate, so I need the TEV to raise the temp within the evaporator.
The issue suddenly started happening on Friday last week. Unit was running fine until then.
Any help or ideas would be greatly appreciated.
Phil.