how to determine gas enough for free standing chiller

[otto2008]

Hi I am a heat pump installer, but I have a chance to repair the free standing chiller, the volume is around 1 cubic meter and use R22 gas,the client require the temperature at +4 degree celius.
The client said the chiller is not cold enough. When the compressor is running, the gas pipe is hot, but the liquid pipe only warm, so I connect the gauge and it show 0 psi while the compressor stop, so I charge the gas just a little only may be 20g, but the gauge suddenly show to 50psi, and start the cooling process, just in ten minutes the chiller from +15 degree celius drop to +11 degress celius then keep at that point around an hour.
So is anybody can told me what is wrong, at that time the gauge show the low pressure is 30psi.

the next question how can I determine the gas is enough or not?
somebody told me that if your setting temperaure is +4degree celius, so check your low pressure side and adjust it to -6 degree c and around 21 psi that the temperaure inside the chiller should be okay. but other people said by experience, if you can see the frost just at the suction of the compressor, that is enough, if that is a lot of frost that should be too much. so is anybody can tell me how I can charge sufficent gas, thanks.
Regards
Otto

[Grizzly]

Otto.
You need around 6 degrees of sub cooling.
By saying Heat pump installer, what is your actual trade?
Chillers are totally different and if you don't really know what you are doing.
Walk away before you create serious damage to the chiller. Would the customer you are doing this work for hold you responsible for any damage.
System pressure is just one of the parameters used to determine correct operation.

As we say you at this stage "May of bitten off more than you can chew".
By the way where's the leak?
Grizzly

[MikeHolm]

You may also have had a sticky gauge

[AlexG]

Grizzly, good reply!

[otto2008]

Hi Grizzly,
Thanks for your prompt reply, actual my trade is an electrician but I have studied the heat pump as well (the basic from polytechnic), the client is my friend, so he let me try, otherwise he will dump this chiller, so just let me learn more, i found the leak from the cap of the charging adaptor, so I secure the cap and check with the soap, that is no bubble, but I am not sure how much gas or may be have some air go to the system, but the name plate was missing, so I don't how much gas I need to charge back, after I recovery the gas and vacuum the system. So for sub-cooling is I measure the temperature from the condenser side for 6 degree, please can you give me more details.
Thanks for your kindly assistance.
Regards
Otto

[install monkey]

otto-your comment" leak from the cap of the charging adaptor, so I secure the cap and check with the soap, that is no bubble"-was this soapy water? or leak spray-what was the ph level of the soap? were ur gauge lines new so maybe the schraeder core wasnt depressed hence the delay in reading the pressure- u might of introduced air into the system - based on were ur gauges zero'ed before connecting,did u purge ur lines before adding the 20grm of gas- suction pressure whilst running is typically 58-60 psig (4 bar) is the condenser coil clean- maybe get hosepipe on it to wash the crap out from between the fins

[otto2008]

Hi install monkey,
Thanks for your advice. For the soap I said, i used the big blue, special for leak test liquid. I have check the condenser coil, it is clean, but may be the system already has air inside, because when I open the cap of the charging adaptor, it was leak from the adaptor. so when last time I charge the gas I have purge before I charge, I put another adaptor to the suction side before the inlet of compressor. but the gauge was show 0psi last time. but when I charge about ten second and closed the valve, which suddenly go to 50psi, just few second. and the cooling effect is coming back from the evaporator. but only drop from 15 degree to 11 degree celius, then no further drop. But before the client compaint is no cooling effect.
So is that better to recovery the system, replaced the leakage adaptor, vaccum the system for at least 6 hours, then put the gas back to the system, please give some advice and when I charge the system, I will check the superheat at compressor inlet (use the thermostate sensor touch the suction of the compressor to measure the temperature) and the suction pressure and convert it to the temperature and subtract them is that around 10 degree F, also check the sub cooling from the outlet of condenser and discharge presure convert to temperature, if around 10 degree F (or 6 degree c) should be okay, if more than 10 degree F, let say 20 degree F, that may be condenser dirty. but if the superheat is around 10 degree F, that may be okay. so please kindly advice is this the correct checking.

Regards
Otto