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Thread: R134a operating pressures
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07-05-2008, 11:21 PM #1
R134a operating pressures
Hi there ,
I am hoping that someone will be able to assist me here.
I have a cold store that I am trying to get working.
The client called me to site as the evaporator was completely blocked with ice.
In short I checked the condensate drain, and pump
checked for pressure drop across the filter drier in the liquid line - it was ok
Suction pressure was just about 10 psi and discharge at about 80 -100.
checked the subcooling which was normal ( i doubt this now having said that!)
and as such deduced that there muct be a restriction in the flo of refrigerant. with no other area to check ( i checked the operation of the solenoid valve in the liquid line also by the way)
I deciided to change the orifice in the expansion valve.
I started up the system and it happily came to temperature.
I was then called back to site with the same problem.
I then noticed that the fans were not running and noticed that the evaporator sensor was reading very high and had a sensor fault.
I replaced the sensor and started the system again which soon came to temperature.
I was then called back AGAIN .. .guess what ...same problem... this time the controller was playing up and the manufacturer reset it ovver the phone and the sensors were reading correctly again .
Back again this time with the same problem.
I am now thinking that the system is short of gas, but i dont want to overcharge the system.
The cold store is supposed to be running at 2-4 deg C and i seem only to be able to get about 12 psi onn the suction side.
Could someone please tell me what sort of pressures I would be expecting on this type of r134a system.
I charged the sstem to the sight glass which is free from bubbles. I am just worried that I may over charge it if I am not careful.
Failing all of the things above the only other thing i can think of is the TEV bellows not working correctly.
I have checked the phial which seems ok and is placed correctly.
As I left the system the evaporator was frosting about half way down.
But i fear I may ave over charged it as the condenser had a great TD between the top and the bottom of the condenser.
Really frustrated with it and so is my client.
Any ideas / help would be appreciated.
Chilly Matt
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