add sight glass on critically charged system

[clearchris]

Hi.

I had to cut up a sandwich table to replace the compressor, so I added service valves and a sightglass. I also estimate that I have another 3" of 1/4" OD copper to accommodate the sightglass and enough room between the cap tube and next solder joint so I don't plug the cap tube.

So, how much extra r134a would you add to compensate for a sight glass and a few inches of tubing on the liquid line?

Thanks!

[monkey spanners]

Can't see it being more than 5 grams, think a 72" gauge line holds about 20/25 grams of liquid. I'd start by putting the correct factory charge in and monitor the system, then put a bit more in if needs be.

[Peter_1]

Capillary or TEV expansion?

[1mikeefc1]

With you putting in the sight glass in it you should be able to charge till its not flashing and will be ok.

[monkey spanners]

With you putting in the sight glass in it you should be able to charge till its not flashing and will be ok.

I don't think they run with a full liquid line, at least the bigger systems don't. On these if you charge to a full sight glass they will flood liquid back, or not reach temperature as the evaporation temperature won't go low enough.

[clearchris]

It's a capillary tube system. No receiver. Fairly small system with a 1/4 hp compressor. I would have converted it to TXV, but there just wasn't room for the extra parts. Getting the new compressor in was really tight.

Right now at the charge specified by the label (7 oz) the sight glass is full except for maybe 3mm at the top.

I think what I'll do is get it back into place, loaded with product, at holding temperature and meter in up to 1/4oz (roughly 5 grams per original poster). If the sight glass fills before I meter in 1/4 oz, I stop and call it good.

I'll report back with results. Thanks everyone!

[lowcool]

in my apprentice days with r and d a fine continual stream of smaller "bubbles" was the indication from a correct charge in a well designed system with domestic refrigerators

[ATR]

Not to be a smart ass but the manufacturers put the exact weight of refrigerant needed for optimum performance so you really shouldn't need a sight glass. It may end up getting you in trouble, or a tech down the road, when those little bubbles are seen and you just can't help but add a shot.

[1mikeefc1]

I would say 80 percent of manufacturers data plates i have worked on are wrong when weighing in refrigerant charge. Extremely unreliable and these are warranty jobs as well as older equipment.

[The MG Pony]

I all ways charge via SH on cap systems, it takes all the guessing out of it, once it is at operating temp you want 20k for the SH. the sight glass is as use full as tits on a bull, for a cap tube system, what on this earth possessed you to put one in?