Hello and Help needed with refrigeration charging

[Mastercool]

Hello, this is my first time on the forum. I live at the Victoria Falls, Zimbabwe and have two small refrigeration companies, one at the Victoria Falls & the other in Livingstone, Zambia.

Could someone help with general refrigeration charging proceedures. I know that the relationship between pressure & temp is always constant. However, it seems that when a refrigeration cycle is started, the compressor will create a drop in pressure on the suction side of the system, ( Assuming that an "Expansion Valve is used). In other words the temperature as measured against the existing pressure at the suction side will not be the actual temperature of the refrigerant. It seems to be lower. If this is true how does one charge the system correctly and how do you avoid OVER charging. Very often a "FULL" sight glass will result in an over charged system. Also bear in mind that, in this part of the world, where is almost impossible to obtain any spares (NOT EVEN A PENCIL DRYER) one comes accross a lot of mismatching, home made evaporators and totally unbalanced system. I have just repaired two systems, one using a R502 expansion valve in an R22 system. The other using R22 gas with a R12 expansion valve.

Thank you.

[Brian_UK]

Hi Mastercool and welcome to the forum.

It sounds that you have fun deciding what your systems will produce...

With regard to deciding if proper charging has been achieved it does depend very much on whether the expansion valve, or capillary, is sized correctly and working properly.

If you measure the superheat at the evaporator and at the compressor suction pipe you will get an good indication of how well the system is running.

Measure the suction pressure and convert that pressure into a gas temperature, now measure the pipe temperature at the compressor inlet. If the difference in temperature between the two readings is around 8°C to 10°C then things shouldn't be too bad.

If the temperature difference is very small, less than 5°C, be very careful as liquid refrigerant could enter the compressor during the operating cycle and cause damage to the compressor.

If the temperature difference is high then compressor cooling will suffer.

Hope this helps.