The "optimal" charging pressure...?

[MutantToad]

Hey everyone,

A question on charging: Is there any one "perfect" charging pressure? Or is it dependent on many factors? If it is the latter, can someone tell me what these factors are and how to determine the charge? (No one likes an over/undercharged system, right?)

~Toad

[_HL4E_HalfLife_]

Hey everyone,

A question on charging: Is there any one "perfect" charging pressure? Or is it dependent on many factors? If it is the latter, can someone tell me what these factors are and how to determine the charge? (No one likes an over/undercharged system, right?)

~Toad

There are soo many factors its not funny! Charging factors include compressor size,tubing size,tubing length,gas type,heatload,etc.

The only real way to charge a system is using manafold gauges and charging it based on low side pressure and ur evap temp.

[MutantToad]

Damn. So how can I determine it? I don't want to pay for a HVAC shop do it. And what temperature/pressure sensors do you recommend?

[Cr@sh_D1n3r]

There is no right pressure on a system. The charge is by weight not pressure. You can't use the low side gauge yet if you didn't used about the right expension device. You at least need to calculate the right heat load first then use the right valve. After that you could start playing with pressures.

[kayl]

dont forget at room temp ya got both liquid and gases in there.
it all depends on room temp at what pressures will be.
check out the refrigerant charts and see what i mean.

if ya paying some one to charge just get them to put lost in and charge it at load once ya get home, ie releasing gas lilttle at a time till the compressors isnt frozen over anymore.
you will need to do it perfect first go other wise ya stuffed.

[chilly1]

First what system are you charging, tell em the capillary tube size, compressor size and what you wish to run it on.

[MutantToad]

Say I wanted to charge a R-402A system, capillary tube 20 ft of .028in (is that about right?), 1/2HP compressor. Room temp around here is 70-80*F. Load will probably be 250-300 watts (A64 X2 4400+ almost OC'd to hell.)

[the_new_guy]

i think the cap tube is too long it should be about 5' or less

[labrat23]

Here is what I used to guess my cap tube length.
http://www.xtremesystems.org/forums/...ap+sizing+rule

I have tweeked it much yet, but I think garry was right on for my r404a system. I dont know if it applies to a r402 system though.

[_HL4E_HalfLife_]

There is no right pressure on a system. The charge is by weight not pressure. You can't use the low side gauge yet if you didn't used about the right expension device. You at least need to calculate the right heat load first then use the right valve. After that you could start playing with pressures.

How can u charge it on weight when u dono how much ur system takes in the first place???

[kemod]

I usually static charge my R-22 to full charge it can take at room temperature. Run it til it gets cold and dynamic charge it on under load to get right amount of refrigerant (coldest temp)

[wdrzal]

How can u charge it on weight when u dono how much ur system takes in the first place???

you can't, so that leaves either a sight glass or by superheat.

[Cr@sh_D1n3r]

How can u charge it on weight when u dono how much ur system takes in the first place???

My point is that if you want to charge a system and don't know how much to put in, each time you will change the expension valve or w/e on the system, you won't ever know how much you need. When you know how to recharge a system propertly, you should always know how much to put in. If you don't, each time a refill is needed, you will have to calculate superheat.

[MutantToad]

i think the cap tube is too long it should be about 5' or less

Yeah...I meant 20 inches, but that may be a bit low.

[MutantToad]

kayl: Would it work if I did what you said, with a sight glass on the suction line? I could have the guy who charges it overcharge it, let some gas out, and use the sight glass to measure if it is charged correctly? (What do I look for in a sight glass for the optimal charge?)

[Cr@sh_D1n3r]

you need a sight glass on the liquid line before the cap line. If you want one on the suction line it's not a bad idea but you can charge the system with a load on it when you'll have a superheat of about 10c your charge should be right. When looking in the sight glass, the liquid line needs to be full and the one on the suction should be empty from liquid.

[wdrzal]

A cap tube should have a liquid seal,so a sight glass should be full on the high side, A suction line sight glass should just have a occasional drop of refrigerant pass thru, once the evap starts spitting out liquid its doing the best it can, completly flooding the evap is no good either.

be carefull a full sight glass looks the same as a empty one. I just purchased a couple glasses thathave a dot that the liquid magnifies and makes it look elongated so you can tell the differance.


use this type and no one can say it acts as a receiver cause its straight thru with the same internal diameter as the tube.

[MutantToad]

you need a sight glass on the liquid line before the cap line. If you want one on the suction line it's not a bad idea but you can charge the system with a load on it when you'll have a superheat of about 10c your charge should be right. When looking in the sight glass, the liquid line needs to be full and the one on the suction should be empty from liquid.

Before the capillary tube? According to most phase change info sites, most of the refrigerant condenses in the capillary line, so will there be much liquid in the sight glass? Again, sorry for my n00biness

[saratoga]

Pressure is greatest before entering the cap tube, so I don't think you're going to condense a whole lot of refrigerant in the captube itself unless your condensor is undersized.

[wdrzal]

that where I part with every thing that is said. refrigerant condenses in the "condensor" not the cap tube, a cap tube must have a liquid seal to work properly.

[Stewie007]

Before the capillary tube? According to most phase change info sites, most of the refrigerant condenses in the capillary line, so will there be much liquid in the sight glass? Again, sorry for my n00biness

Don't worry about your "noobiness," just be careful where you get your information.