To use sight glass or not

[marter]

ISo the other day I had a walk in cooler low on gas. R22 to be exact, I found and fixed two leaks. Had a coworker bring me some more r22. After installing a new fan cyce control begain charging the unit. Got the box to 42° with a 20° superheat and then box was down to 38° when I left.

Ive always been told to keep a full glass to ensure all liquid to txv. Manager says to charge to the correct superheat and not worry how full the glass is and coworker says only with R22 you should charge to a full glass

[ryan1088]

First of all, does this have a headmaster or just a fan cycling control? Also remember a sight glass is a tool, like any other tool you need to know when to use it and and what it's telling you.

[jpsmith1cm]

A TEV MUST have a solid column of liquid to it in order to properly meter refrigerant.

I would install a sightglass on any equipment with a receiver.


I would NOT "charge to superheat" This is incorrect procedures for any walk-in that I've ever worked on.

[marter]

No headmaster just fan cycle and yes it does have a sight glass

[coldjoe]

Problem with fan cycling on single units is it plays havoc with sight glasses .if fan speeds up quickly its drops condenser pressure quickly and pulls liquid back into condenser and bubbles in the sight glass,very easy to overcharge system using sight glass on this scenario.Most of the fan controls on single units i come across tend to ramp up and down very quickly

[markettech]

Manager says to charge to the correct superheat and not worry how full the glass is and coworker says only with R22 you should charge to a full glass

If the TXV does not have a solid column of liquid to work with, how is it supposed to maintain a 'correct superheat'?

[marter]

I understand this but he signs the paycheck.

[marter]

A field installed unt no weigh in charge, you would have to have some type of head pressure control to handle low ambient tempreture though.

[markettech]

I understand this but he signs the paycheck.

You don't have to prove a flashing sight glass via a picture, I would hope. Why can't you properly charge the unit (clear the sight glass) AND keep the boss happy by simply saying you charged the unit to XX superheat?

A field installed unt no weigh in charge, you would have to have some type of head pressure control to handle low ambient tempreture though.

Headmaster would be the way to go.

[jpsmith1cm]

You don't have to prove a flashing sight glass via a picture, I would hope. Why can't you properly charge the unit (clear the sight glass) AND keep the boss happy by simply saying you charged the unit to XX superheat?

Bingo!

Do the right thing and tell the bossman what he wants to hear.

[ryan1088]

There's a way to respectfully argue your point to the boss who you work for. Have your facts straight (which you are trying to do by being here) and just state your disagreement and back it up with why. Explain you will make him more money by doing it the right way the first time.

[Capz]

If fan cycling is throttling my pressure up & down, first I make sure the fan control is set up as accurately as possible for the refrigerant being used. Then I try and maintain a head pressure of 180 (R22) maybe using a piece of cardboard to partially cover the condenser and then can watch the sight glass and clear it at this point. If I still see bubbles at a lower head say 160psi, I might add small amount more but being careful not to over charge. I don't even call the boss. I am the boss...

[2sac]

I understand this but he signs the paycheck.

and when the call comes back in you were the tech who worked on it last...

Try blocking off the condenser like Capz suggested

[barbar]

All ways an interesting one.
As stated above a sight glass is a tool and used as an aid to charging, generally speaking your pure refrigerants, are normally better than mixtures using a sightglass method. (with mixtures very small pressure drops, valves, driers etc. can cause bubbles) At times of very high load, it sometimes difficult to get a full sightglass when the valve is 100% open especially the TXV is slightly on the larger size of the required duty.
Superheat is also a good method, but normally only when your room or product (one pass chillers) is close to set point.
So it more down to understand at what stage your system is at and what condensing control you have. (also stated above)

[Snapperhead]

The only time you cant use a sight glass is when you have a headmaster , because even after the sight is cleared you still need to add a little more , and there is a procedure for measuring that amount.

[QTEMP]

This one never goes away.......it depends on what type of system you are working on. The answer to this question is always yes. However, it depends on what type of system you are working on. The debate rages on that if you have a full column of liquid in the liquid line you should have a clear sightglass. On cap tube systems, due to may reasons, the sightglass may always flash and never clear. There is a better reason to use a sightglass on systems. And that is for moisture reasons. I have my guys install sightglasses on all refrigeration systems for this very reason. On top of that, they are a great way to visually check the refrigerant charge on any system along with any moisture issues. Although charging by superheat on cap tubes in the best way, second to weighing in the charge, I don't think charging a system by superheat, let alone sub-cooling is the correct way either. What is the correct way? By using the recommended refrigerant charge on the piece of equipment. If no tag is available, then I usually just let the system equalize after a recovery, pressurization, deep vacuum and let the refrigerant fly in under pressure until equalization occurs. You will be pretty close to a full charge. As far as sightglasses on ice machine, I recommend installing them for moisture indication purposes and a quick visual check of a refrigerant charge. MOST of the time, a clear glass is a full or overcharged system.

[Snapperhead]

I never see a sight glass on cap tubes , i usually have to bring out the crystal ball

[QTEMP]

I never see a sight glass on cap tubes , i usually have to bring out the crystal ball

Smart man

[Capz]

I never see a sight glass on cap tubes , i usually have to bring out the crystal ball

Crystal ball? What's wrong, don't you have x-ray vision?

[bunny]

Got the box to 42° with a 20° superheat and then box was down to 38° when I left.

Ive always been told to keep a full glass to ensure all liquid to txv. Manager says to charge to the correct superheat and not worry how full the glass is and coworker says only with R22 you should charge to a full glass

Your statements here raise a few questions:

Did you charge to a full sight glass, or charge to superheat as your boss requires?

In either case, why was the system operating with 20 deg superheat?

What does your boss want the SH to be?