jmc88
19-07-2011, 10:41 AM
I was working on a a -20 room that was run on R417a and it had only been achieving -12. The previous engineer that had been out to it couldnt get it lower than that so he recommended it be retrofitted for R404a. I went out and retrofitted it to R404a, new oil, exv, drier etc but the system can only achieve -15. Apparently the system has worked prevously but i have my doubts as to whether it was achieving -20 and pumping down etc or just struggling by to reach around -18 running non stop as thats what thy said the room used to be at.
My running pressures are suction- 7 psi and discharge- 210 psi. The only way to get my suction pressure/temp up is to adjust the expansion valve out but any further out that 1 1/2 turns from factory setting causing the evaporator/compressor to flood with liquid. Any adjustment in from factory setting loses cooling so there isnt much adjustment i can make to it.
I am getting sub cooling of 4C but superheat of 21C but i can still get a high/false superheat reading with liquid slugging at the compressor after a slight adjustment of the exv??!
I am pretty sure the charge is correct, 10.5 kg, i had it running for a day with 9.5kg in also before adding an extra kilo to no effect. (I recovered 11kg of R417a before the retrofit)
I have tried various things to try and get the temp down but i cant get it any further than -15
Ive checked all the obvious things at the evap, correct air flow through evap, clean coil, evx bulb is in correct position, I even disconnected the exv and blew through down through the evap with nitro down to the suction to see if there was any oil or sludge or anything sitting inside the evap but there was nothing.
Anyone else any ideas?
Here is the details of the system, is it sized incorrectly??
Evaporator
Searle KM80- 6L
R404a
Capacity- 9.74 X 0.6 correction for minus 30 /6C td ..5.84Kw on R404aAir Volume= 2m2/s
Surface area= 34.5 m2
internal volume= 8.4 dm3
inlet- 5/8th outlet- 1 1/8th
Distributor= 6 x 1/4 pipes
Room Size
6570 x 3940 x 2130 high
Approx 2000 cubic feet
Expansion Valve
TES 2
R404a
Orrifice -No.4 = 4.5 KW
Compressor
input = 3.6 KW
RPM = 1450
Condensing Unit
Prestcold
MALGV 95 JA B4
Assembly no. 34800523
Comp replacement- 6711302
Run amps- 13 A
Comp- 3.6 KW 440/480 60HZ
Fan- 0.18 KW 440/480 60HZ
FLA- 0.7 LRA- 2.4
High pressure- 31 Bar
Low pressure- 19 bar
Serial- 0101 AH
Liquid Reciever
Copeland
Serial- USB 12586
Model- M114
Int vol- cub ins 696
litres- 11.4 litres
Test pressure- 32.3 bar
Pipe sizes
Suction- 1 1/8th
Liquid- 1/2
Approx 20M pipe run, approx 15-20 bends. Evaporator is located above condensing unit.
My running pressures are suction- 7 psi and discharge- 210 psi. The only way to get my suction pressure/temp up is to adjust the expansion valve out but any further out that 1 1/2 turns from factory setting causing the evaporator/compressor to flood with liquid. Any adjustment in from factory setting loses cooling so there isnt much adjustment i can make to it.
I am getting sub cooling of 4C but superheat of 21C but i can still get a high/false superheat reading with liquid slugging at the compressor after a slight adjustment of the exv??!
I am pretty sure the charge is correct, 10.5 kg, i had it running for a day with 9.5kg in also before adding an extra kilo to no effect. (I recovered 11kg of R417a before the retrofit)
I have tried various things to try and get the temp down but i cant get it any further than -15
Ive checked all the obvious things at the evap, correct air flow through evap, clean coil, evx bulb is in correct position, I even disconnected the exv and blew through down through the evap with nitro down to the suction to see if there was any oil or sludge or anything sitting inside the evap but there was nothing.
Anyone else any ideas?
Here is the details of the system, is it sized incorrectly??
Evaporator
Searle KM80- 6L
R404a
Capacity- 9.74 X 0.6 correction for minus 30 /6C td ..5.84Kw on R404aAir Volume= 2m2/s
Surface area= 34.5 m2
internal volume= 8.4 dm3
inlet- 5/8th outlet- 1 1/8th
Distributor= 6 x 1/4 pipes
Room Size
6570 x 3940 x 2130 high
Approx 2000 cubic feet
Expansion Valve
TES 2
R404a
Orrifice -No.4 = 4.5 KW
Compressor
input = 3.6 KW
RPM = 1450
Condensing Unit
Prestcold
MALGV 95 JA B4
Assembly no. 34800523
Comp replacement- 6711302
Run amps- 13 A
Comp- 3.6 KW 440/480 60HZ
Fan- 0.18 KW 440/480 60HZ
FLA- 0.7 LRA- 2.4
High pressure- 31 Bar
Low pressure- 19 bar
Serial- 0101 AH
Liquid Reciever
Copeland
Serial- USB 12586
Model- M114
Int vol- cub ins 696
litres- 11.4 litres
Test pressure- 32.3 bar
Pipe sizes
Suction- 1 1/8th
Liquid- 1/2
Approx 20M pipe run, approx 15-20 bends. Evaporator is located above condensing unit.