best way to charge a system

[VIXS]

Hi There All

I have a Uniflare Dx unit at work and its lost all its charge (R407c)

I have spoken to Unflare and they say you must charge the unit untill there is no more bubbles in the sight glass.
Now i know this is how things were done in the old days but i think we have moved on and the manufacturer should be able to tell you how much charge in kg is needed.
I have looked at the commisioning sheets and it says 32kg, i think this is crazy because the unit is a 30kw serving one circuit with a condensor 55 meters away.
I phoned the installation company and they say no it must be 22kg.

I have tried charging the unit untill all bubbles are gone but that does not work because the unit took 35kg.

Please tell me if i am wrong but when you have a externally equalized electronic expansion valve and a variable fan speed controller on the condensor fan and the possiblity of your filter drier creating a small amount of bubbles, does this not make it very hard to get the correct amount of gas.

I will try to charge the unit going according to the superheat value of 7. does this sound like a good idea........

[monkey spanners]

Took out some 15Kw (sda0501)ones that had 15kg R407C per system, 7/8 and 3/4 pipework, don't know the pipe length, never did find the condesers.......
The ones i worked on had a small reciever on the indoor unit and a tev, this needs a constant feed of liquid.Is the fan speed control on the condeser working ok? What pressures/temperatures was it runing at?

Jon

[VIXS]

The fan speed controller is new and it does not have any markings when setting it up. its just a screw that increases or decreases the tension

[taz24]

Hi There All


Please tell me if i am wrong but when you have a externally equalized electronic expansion valve and a variable fan speed controller on the condensor fan and the possiblity of your filter drier creating a small amount of bubbles, does this not make it very hard to get the correct amount of gas.

I will try to charge the unit going according to the superheat value of 7. does this sound like a good idea........

You need to measure the liquid subcooling if in doubt.
Suction superheat will not tell you the whole story.

Not seeing the system run I would not be able to coment on the sight glass but from experience with 407 you may well see bubbles even though it is charged up.
I would charge the system untill the refrigerant was flowing full volume through the glass.

Liquid subcooling will tell you when there is sufiecient liquid in the system.

taz.

[chillyblue]

Hi

This may help i'm not sure, download the refrigerant calculator from the Defra, ior or DTi website. It is a excel spread sheet for calulating refrigerant charges for the new Fgas law. It may give you a indication if you are near.

CB

[wkd]

Try forcing the fan to full speed and re-check the subcool and sight glass.You might want to query the line sizes are there any high pressure drops throughout the system,also what caused the gas to be dumped?

[VIXS]

Thanks for all your replys

The reason the gas was lost in the first place was because it lost its charge via a leak on the fan speed controller, which has now been changed.

Will it not be difficult if I use the sub cooling to determine the correct amount of charge because if the fan speed controller is not set correctly then this will make a big difference on my sub cooling reading.

The fan speed controller has no markings when you set it.

The pipe sizes are 7/8 and 3/4

I will get there in the end.................

[Entropie]

It is neccessary to run the unit and the condenser fan at full load/speed (best in design conditions) when you chargeing the system. Start with the charge contained actually in the system and then adjust liquid subcooling to 5-7K by adding or removeing refrigerant.

[Lowrider]

When a electronic expansionvalve is used superheat should be between 3 and 5K. Subcooling, if a Uniflair condenser is used, should be between 8 and 10K.

Standard the Johnson control fanspeed controllers are set to high. Try and get it to go on at 15 bar and set the hysterese on cut off so in winter the fan will run low or not at all!

Which company supplied it?