How to charge empty 2 stage cascade system?

[Miko]

dear gurus,.

I would like to know how do we charge an empty 2 stage cascade system?

What is the step of doing this? ANyone have good links or perhaps a guide?

cheers..

[micknick]

Low stage is charged with a static pressure noted on nomenclature plate. If your refrigerant available is different than what is noted you may need to make some adjustments. R-23 for example should be lower due to the higher head pressure. Note amp draw and head pressure if dealing with different refrigerants. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
High stage charge by sight glass, make sure the low stage is operational for load.<o:p></o:p>

[norseman]

dear gurus,.

I would like to know how do we charge an empty 2 stage cascade system?

What is the step of doing this? ANyone have good links or perhaps a guide?

cheers..

Hi Miko.

The way is basically to start charging the low stage first and be sure that the all system is at an ambient temperature. Most brands use a static fill pressure and it should be stated on a label or in the manual. Most of the low stages use an oil return agent as
R 290 (Propane) or less funny liquid Pentane. Check this out because either would best be charged as the first item. The refrigerant can be several types, but if you can make the original, it is easier to stay with the same charging pressure as stated. It is important to charge slowly so you not pull too much cold into the system. You can end up with an overcharge due to the cold system. Important to use both suction and discharge side of the system and be aware of any extra tank who can be on the suction side. If they have such, it is often connected over a thiny capillary tube and will use a certain time to pick up the static pressure. Some brands give the static pressure as a working pressure and that gives you some extra job. In such cases, you have to warm the unit up totally after a run and recheck the pressure.
In such cases, I put an extra 10% charge by filling so the test after a run is likely to be near what I should have as a working (static) pressure. Some gives only the charge by weight, still on small systems! If the high stage use capillary, it is important to use a correct charge so you keep the evaporation temperature and cooling capacity correct. Pretty important for the both stages duty. The HX (first stage) temperature you find will be abnormal low without load from the low stage. I am into -40c R134A and -50c 404A as normal. Mention this because many try to fill up over the stated amount due to what they find as a suction pressure on the highand do not believe it. Stick with the label for the charges. PS: If the refrigerant on the low are R23 or R 508B ( Old? R13) you can charge as gas to minimize the cooling effect the refrigerant can make on the system to avoid overcharging. ( If any mix gas, charge as liquid. Use a fine needle valve on the high pressure bottle as they are or lucky me use a standard gas regulator on the bottle. (PS: Only as gas charging by using a regulator) Good luck ;)