Cant get bubbles out of sight glass

[garyed]

It sounds more like a dirty evaporator coil or low air flow but I suspect dirty coil. It can still cool O.K. depending on how much demand there is in the conditioned space. A dirty coil won't necessarily show a low TD but will show low SH. I also agree with the others about no need to worry about bubbles in the sight glass, especially dealing with a piston system.

[nismo1]

^
X3

FWIW, I had a similar job a month ago. SC was where it was supposed to be but the SG was not clear... I was told a TXV needed a full column of liquid to work properly so I kept adding juice. I couldn't clear the SG to save my life... After way overshhoting the SC and still seeing bubbles, I decided to forget about the SG and just focus on the SC.

Hope that helps...

Yep, had a unit early in my career that I charged by site glass, operated great when I left it, next day call for no cool, go back 30* sc, sh&@! Set sc at 10* and no call back. DO NOT CHARGE BY SG, period!!!

[millertime77]

Thanks for all of your guys help. Experience says that airconditioning should always have a solid column of liquid, and refrigeration, in low ambient, is the only time you should see bubbles. I think it could be a problem with the piston(in backwards, or moving around a little, like someone mentioned), and probably a few other possibilities, but what are you going to do. If it isn't broke don't fix it. By the way I have checked the evap coil, and it isn't dirty, and I changed the filter. I think the sight glasses should be used in medium and low temp applications only, not air conditioning. Thanks to all.

[SBKold]

A sight glass is a useful tool on any system regardless of low temp or high temp. IMHO. Its function does not change because it is on a ac unit.

Its a nice tool meant used in conjunction with (not in leiu of) all the others.

[incontrol]

Sightglasses are for TXV systems ONLY. Take it our or tape it up!

[koolking1701]

I agree. Sight glasses can be useful on TXV systems but are worthless on fixed bore metering devices. Never use a sight glass on any refrigeration, ac, or heat pump with a fixed bore. Get back to basics and check superheat based upon the inddor dry bulb temp and the outdoor ambient temp.

[koolking1701]

Sorry. I meant to say indoor WET bulb and outdoor ambient

[shaka]

Txv or fixed orifice
Sight glass should not be used to determine the charge on small resi equipment.

Its not true that only on low ambient condition will cause bubbles on sight glass
High indoor loads will cause bubbles too
Dirty condenser
extreme outdoor temp
Long liquid line on the roof (flash gas)
Long vertical liquid line (pressure drop)
Non condensable
Blend refrigerant high temperature glide.
Restriction upstream of sight glass
Wide txv hunting
Unseated orifice
Gas heater is running the same time

Sorry that's all I could think off right now.

[WhiteSoxFan]

High indoor loads will cause bubbles too

Please explain how. Not that I disagree, I just want to understand why.

[knewguy]

Please explain how. Not that I disagree, I just want to understand why.

With more heat to reject at the condensor there will be less liquid building up in the condensor the hot gas will take longer to change state to liquid.