To clear or not to clear????

[270wsm]

When are equipment manufactures going to get together with TXV manufactures and come up with a right answer on whether or not to clear thre sight glass with blends? I worked on a large air dryer the other day and notice the sight glass flashing quite a bit. This thing had a large reciever and even had a subcooling loop after the reciever that made another pass through the coil before the sight glass. After talking to the Manufacture about some other issues, I told the guy that I cleared the sight glass, and he told me that I over charged it and to recover some gas back out until the sight glass looked milky. Whats the point of a subcooling loop if your not getting any subcooling?

[smilies]

With receiver, I clear it.

[icemeister]

This has been misinformation from the outset when these interim replacement blends were first introduced.

On system with TEVs and receivers I have always cleared the sightglass...hundreds of systems over nearly 20 years and have never had any indication of overcharging.

Consider a typical air-cooled, outdoor condensing unit with a 45 lb receiver and a Headmaster condenser flooding control. Let's say it's an existing R12 system, you are retrofitting it to R409A and charging it up on a warm summer day, it takes 30 lbs of R409A to clear the SG. Then you take your calculated winter flooding charge of 10 lbs and add that. Is it now overcharged? No.

[Octopus]

Sight glasses are useless, superheat and sub cooling will tell you everything. If you tell guys to clear the sight glass if it has a receiver your going to have a bunch of guys dumping gas into a system with a frozen evap, or a bad evap fan motor or a stuck txv forget it theres hundreds of reasons for a sight glass to be flashing and if you check your superheat ans sub cooling you don't need a sight glass.
Ps.
I'm sure after I said this someone will come back on here and give 100 reasons to have a sight glass.

[hvac248]

Sight glasses are useless, superheat and sub cooling will tell you everything. If you tell guys to clear the sight glass if it has a receiver your going to have a bunch of guys dumping gas into a system with a frozen evap, or a bad evap fan motor or a stuck txv forget it theres hundreds of reasons for a sight glass to be flashing and if you check your superheat ans sub cooling you don't need a sight glass.
Ps.
I'm sure after I said this someone will come back on here and give 100 reasons to have a sight glass.


Gages,thermometer,and PT chart is what I use for a sight glass.
I'm with you!:.02:

[icemeister]

If you tell guys to clear the sight glass if it has a receiver your going to have a bunch of guys dumping gas into a system with a frozen evap, or a bad evap fan motor or a stuck txv forget it theres hundreds of reasons for a sight glass to be flashing and if you check your superheat ans sub cooling you don't need a sight glass.


What's going to stop those same guys from dumping gas into a system while monitoring the subcooling?

I've seen the results of A/C techs who serviced commercial refrigeration systems, insisting on achieving 10ºF-15ºF of subcooling and not using the SG. The systems were all grossly overcharged tripping the high pressure safety control.

Subcooling on these systems is what it is. You can't increase it by adding more charge....until the receiver is 100% full. :eek:

Therefore, I say when working on a commercial refrigeration system with a receiver, subcooling is useless. ;)

[Phase Loss]

:ditto: charging by subcooling on a system with a receiver is like trying to bite your own ear.

[Octopus]

lol all systems do not have a receiver, superheat and sub cooling receiver or not it will tell you allot and you should never charge a system by just sub cooling I said superheat and sub cooling together will tell you everything nobody said anything about charging to 10-15 degrees of sub cooling. You are the tech you are servicing/installing the system you should know how the system is to perform sir not set numbers. Personally I take into account superheat sub cooling, amp draw, performance curves. air flow, water flow, condenser approach, evap approach, delta t, humidity, and all of the other regular numbers etc etc... I cover all of my bases including looking at what the manufacturer suggests after all they made the thing.

The point was and is you cannot rely on one thing to diagnose a system/ charge a system. If you could just clear the sight glass on every system that had a reciever well holy crap.

[surenuff]

with a reciever, I have never had problems clearing sight glass. with out reciever, I have always charged about 80% of original charge if I knew what it was supposed to be, and then adjust from there if needed. I am pretty sure the reason we were told not clear sight glass it the fact that most new refigerants ran a slighty higher head pressure than the original and required more condensor space than what we had. So if you did clear, you were overcharged.

[Phase Loss]

OP has a receiver.

Charge by full sight glass and good enough receiver level for different load conditions and or flooding valves.

all the other fancy readings can be saved for critical charges.

[crackertech]

With a receiver clear the SG.

[surenuff]

OP has a receiver.

Charge by full sight glass and good enough receiver level for different load conditions and or flooding valves.

all the other fancy readings can be saved for critical charges.

i read that, thanks

[VTP99]

What about the FLOWING RIVER sight glass on low temp apps. I like to leave that flow. :anyone:

[270wsm]

My main concern is getting all liquid entering the TXV. I have been told time and time again, in sporlan classes and other classes, that the TXV MUST have only liquid entering it or it will not work properly. In my example in the first post, the sight glass was right before the TXV and was flashing.

[hvac248]

[QUOTE=270wsm;6455772]My main concern is getting all liquid entering the TXV. I have been told time and time again, in sporlan classes and other classes, that the TXV MUST have only liquid entering it or it will not work properly. In my example in the first post, the sight glass was right before the TXV and was flashing.[/QUOTE

1 degree of sub-cooling at the TEV will provide liquid ,5 degree will give you a better control over varying load conditions. most SG I have seen lately are far away from the TEV which would lead me to clear the SG , but in reality the sub-cooling could be lost by the time it got there, so if the receiver is not sized properly the system could be overcharged. Thats why I believe that you can not take a couple of measurements and make a blanket statement on charge,as simple a system is it the Physics that dictate proper operations.

[270wsm]

1 degree of sub-cooling at the TEV will provide liquid ,5 degree will give you a better control over varying load conditions. most SG I have seen lately are far away from the TEV which would lead me to clear the SG , but in reality the sub-cooling could be lost by the time it got there, so if the receiver is not sized properly the system could be overcharged. Thats why I believe that you can not take a couple of measurements and make a blanket statement on charge,as simple a system is it the Physics that dictate proper operations.

I like to try to install the SG right before the TXV when I can. If you cant clear the sight glass without overcharging the system, then a subcooler is needed ( i.e. Liquid/suction heat exchanger). Bottom line is you can't have flash gas entering the TXV and expect it to operate properly.

[rayr]

There is NOT an expansion valve on the market that will work properly without having a full column of liquid entering it. End of Story!!

[270wsm]

There is NOT an expansion valve on the market that will work properly without having a full column of liquid entering it. End of Story!!

:cliff:

[-frozen-ocean-]

I agree with a receiver charge to a full sightglass. do a pumpdown test and watch your head. and if your really good at what u do the one two three mississippi rule can do wonders :LOL:

[surenuff]

I like to try to install the SG right before the TXV when I can. If you cant clear the sight glass without overcharging the system, then a subcooler is needed ( i.e. Liquid/suction heat exchanger). Bottom line is you can't have flash gas entering the TXV and expect it to operate properly.

Other than a grossly undersized liquid line, how could we have a clear sight glass and not have a full column of liq.? How do you lose subcooling as the liquid gets closer to the txv? What benifit could you possibly get by putting the filter drier right before the TXV? Is it going to pick up trash that accumulated in the liquid line better than in the liquid line in front of the reciever????

[270wsm]

Other than a grossly undersized liquid line, how could we have a clear sight glass and not have a full column of liq.? How do you lose subcooling as the liquid gets closer to the txv? What benifit could you possibly get by putting the filter drier right before the TXV? Is it going to pick up trash that accumulated in the liquid line better than in the liquid line in front of the reciever????

Where in my post did I mention a filter drier? It is very possible to have a clear sight glass at the condenser and have flashing at the TXV. I have seen it many times due to pressure drop in the liquid line, a long vertical run where the condenser is lower than the evaporator, and when the liquid line runs through a hot attic and picks up extra heat before it gets to the TXV.

[RoBoTeq]

Always go with what the manufacturer of the equipment states. They are the ones who design the system, so they are the ones who know best what components need to be used and how.

[270wsm]

I agree with a receiver charge to a full sightglass. do a pumpdown test and watch your head. and if your really good at what u do the one two three mississippi rule can do wonders :LOL:

I dont recall ever hearing the three Mississippi rule.

[artie415569]

When are equipment manufactures going to get together with TXV manufactures and come up with a right answer on whether or not to clear thre sight glass with blends? I worked on a large air dryer the other day and notice the sight glass flashing quite a bit. This thing had a large reciever and even had a subcooling loop after the reciever that made another pass through the coil before the sight glass. After talking to the Manufacture about some other issues, I told the guy that I cleared the sight glass, and he told me that I over charged it and to recover some gas back out until the sight glass looked milky. Whats the point of a subcooling loop if your not getting any subcooling?

Not sure what refer you are talking, but I remember a 410-A unit in school I would have 8 degrees of subcool and a few bubbles in the sight glass. Instructor said "some blends do that".I'm not positive thou.

[RoBoTeq]

Not sure what refer you are talking, but I remember a 410-A unit in school I would have 8 degrees of subcool and a few bubbles in the sight glass. Instructor said "some blends do that".I'm not positive thou.
That's about right for R410a. A clear sight glass could always be an overcharged system.

[frozensolid]

Clear the Glass.

The only time I won't clear a glass is if there is a LL sol for temp control, and the box is warm. I'll leave the glass flashing until it is close to set point. Many times the glass will clear as the valve throttles down. If not I adjust from there.

Sometimes on long runs clearing the glass on start-up will give you an overcharge when box gets to temp.

[RoBoTeq]

Clear the Glass.

The only time I won't clear a glass is if there is a LL sol for temp control, and the box is warm. I'll leave the glass flashing until it is close to set point. Many times the glass will clear as the valve throttles down. If not I adjust from there.

Sometimes on long runs clearing the glass on start-up will give you an overcharge when box gets to temp.
Everything I have been taught and in turn taught others pertaining to R410a is that a clear site glass is most likely an overcharge.

[smurphy]

Everything I have been taught and in turn taught others pertaining to R410a is that a clear site glass is most likely an overcharge.

ALL the R-410A Systems I've seen do not have a receiver. This is the refrigeration section. This is the most accurate way of charging a cooler/ freezer with a receiver and sight glass. Also checking the superheat at rated box temp and adjusting as needed.

[RoBoTeq]

ALL the R-410A Systems I've seen do not have a receiver. This is the refrigeration section. This is the most accurate way of charging a cooler/ freezer with a receiver and sight glass. Also checking the superheat at rated box temp and adjusting as needed.
I don't deal with refrigeration, only space cooling systems. This could be the reason for some of the differences of opinion and is why I state to always do what the equipment manufacturer says to do.

[hvac-master]

Do not charge a system with refrigerant solely due to bubbles in a sight glass.


Is the pressure drop across the drier too high? (clogged, undersized)
Is the subcooling sufficient? (According to manufacturer specs)


The following is an excerpt from National Refrigerants:

http://www.refrigerants.com/faq.htm#eight

"There are several reasons for bubbles in the sight glass. If one of the traditional refrigerants showed vapor in the sight glass it often meant there wasn't enough liquid refrigerant being fed to the valve, and more refrigerant was added to the system.

Blends could show flashing for the same reason, however, they can also flash when there is plenty of liquid in the receiver. Ironically, this liquid in the receiver could be causing the problem, particularly when the equipment is in a hot environment. Blends will come out of the condenser slightly subcooled - at a temperature below the saturated temperature of the blend at the existing high side pressure.

Yet when the blend sits in the receiver, it can "locally fractionate," or change composition slightly by shifting one of the components into the vapor space of the receiver. This will effectively produce a saturated liquid in the receiver, at the same pressure you had before, which flashes when it hits the expanded volume of the sight glass. In most cases these bubbles will collapse when the blend gets back into the tubing which feeds the valve, and the system will operate just fine.

Check other system parameters such as pressures, superheat and amperage to confirm whether you have the right charge. Don't rely solely on the sight glass."

:payattention:

[frozensolid]

Refrigerant "sitting" in the receiver of functioning system is a fuzzy point. If you have some time there was a extremely interesting discussion of this in the sub-cooling with receivers thread.

Its a good point to look at what the system as a whole is doing. But I still think a clear glass is a happy glass.

[icemeister]

Refrigerant "sitting" in the receiver of functioning system is a fuzzy point. If you have some time there was a extremely interesting discussion of this in the sub-cooling with receivers thread.

Its a good point to look at what the system as a whole is doing. But I still think a clear glass is a happy glass.

Here's that thread: Subcooling w/Receivers (http://hvac-talk.com/vbb/showthread.php?t=56495)

[RoBoTeq]

I still think a clear glass is a happy glass.
Only when it's filled with a blanco Patron.

[rayr]

I don't deal with refrigeration, only space cooling systems. This could be the reason for some of the differences of opinion and is why I state to always do what the equipment manufacturer says to do.

Refrigeration manufacturers don't say a whole heap about charging a system. 99.9% are field piped and charged. Think Norlake has a precharged system with quick-attach fittings on them for the DIY Deli owner. LOL

[iceman777]

Ditto, smurphy.

If it's your average cooler or freezer, clear the glass, then set superheat @ tev as needed. If box is hot, give time to cool some; glass may clear as tev throttles down. But in general, clear the glass.

Never saw R410A in a cooler/freezer with a receiver.

[rayr]

Ditto, smurphy.

Never saw R410A in a cooler/freezer with a receiver.

Not yet anyway. I have pics of a vegetable market with 4 York A/C condensers serving W/I coolers. They were hacked in and of course I walked away from it. I can post pics if ya want.

[VTP99]

Not yet anyway. I have pics of a vegetable market with 4 York A/C condensers serving W/I coolers. They were hacked in and of course I walked away from it. I can post pics if ya want.

:worthless: