question about split system installs

[frankman]

when you install a split system heat pump do you have to know the exact measured length of line set that you installed in order to get the refrigerant levels perfect or can you charge the system by guages alone? whats the best way to know that your split system has the perfect amount of *****?

[monkey spanners]

If this is a normal American style air con after making sure filters and coils are clean then they are charged by superheat or subcooling depending on if they are cap tube/piston or txv systems. Often there is a chart on the outdoor unit service panel. To know if the charge is correct is just a case of checking air flow is good and then superheat or subcooling as applicable.

If this is mini split system as they are known in the States, then they will come with a factory charge for 'x' meters and if the line set is over this length you will need to add 'y' grams per meter to ensure a propper charge.
You can not charge mini splits by gauge readings, many have inverter driven compressors and electronic expansion valves (EEV) and which will make gauge readings meaningless.
Once the system is charged, mark the extra charge on the unit so the next tech doesn't have to go measuring the line set to calculate it.
The only way to know for sure the charge is correct is to weigh it out and back in again with a recovery machine, cylinder/jug and scales.
Be carefull when doing this as on some units if the EEV is closed you won't get all the charge out, or also if you have pressure tested with nitrogen it may not all be vacuumed out either, there are often extra schreader conections inside the unit that need to be used in these situations, best check with the manufacturers technical dept to be sure.

Jon :)

[frankman]

thanks for the reply jon.im wondering if it would be a good idea to install a site glass close to the metering devise (cap/piston) on split systems then when you see that you have full liquid flow at evaporator you would know that system is full.does this make sense?i mean after vacum is pulled then king valves opened all you have to do is add small amounts of refrigerant until you have steady liquid flow to metering devise. it seems to me that this would be an easy way to know that system is fully charged. do you think this way would work?

[nike123]

thanks for the reply jon.im wondering if it would be a good idea to install a site glass close to the metering devise (cap/piston) on split systems then when you see that you have full liquid flow at evaporator you would know that system is full.does this make sense?i mean after vacum is pulled then king valves opened all you have to do is add small amounts of refrigerant until you have steady liquid flow to metering devise. it seems to me that this would be an easy way to know that system is fully charged. do you think this way would work?

Nope!
Where would you put sight glass? They are usualy heat pump models with capillary. You need two. That also mean that they are critically charged and sometimes it is normal that there is no subcooling at all. That also mean that they need diferent charge in cooling and heating mode.
What is easier than weigh in charge?

[monkey spanners]

What Nike said^, i've seen con rods smashed after people have charged to a full sight glass on cap tube systems. I think a lot of the sytems don't even have an accumilator to catch any excess refrigerant.
On one fixed orifice system i look after, its propper charge is 3.3kg, if you put an extra 50g in it floods back to the compressor! That is only about two gauge lines full of liquid!

Jon :)

[ClimateControl]

Most of the time they fill it with enough to handle a particular footage, and they provide you with a calculation to put more in per meter or foot.