Sight glass again

Techman

Being fair here. I attended an ICOR (hotshot) refrigerant class this evening and they had a little bit on "do not charge to a full sight glass" ,so I asked my usual Q's and I said my piece and tomorrow I get to talk to a top tech at the factory. I'll let you know what they have to say.

Solid_Fuel_Man

Interesting

I was taught to always charge to a full sight glass, have been asked/told "what do you think it's there for" more than once if this was ever brought up.

Taylor

Spence

SG Again

I can't speak regarding low-temp, but for residential DX cooling, I know of no maker who supports charging to a clear sight glass.



In an experiment with an HVAC tech school, we had an R-410A machine stamped 9 pounds one ounce of factory charge. Since the manual told us that was for the OD unit and a 15' lineset, we installed a 15' lineset and the AHRI smallest rated coil. The conditions at the time required 8 degrees of sub cooling (+/- 3 degrees). We had 7, so we were happy with that. We then removed the refrigerant, installed a sight glass, and added refrigerant until the glass was clear. Removal of the refrigerant this time revealed ten pounds three ounces. Proof enough.

Techman

SG again

So, let me get this straight. You have no problem feeding the TXV w/ a saturated refrigerant. Having a saturated refrigerant ( where the SGMI would be) in the LL leaving the cond unit ,is that SC?. I'll go with the 10lb 3oz. to feed the TXV properly. What was the head press diff between the 10-3 vs. the undercharged 9-1 charges? What about the SH ? Suction press would be different also, I think! Interesting!

Spence

SG Again

If my charge is correct, and my sub cooling is correct, how could the refrigerant in the liquid line possibly be saturated? It was 7 degrees below that point; the range where the factory wanted us to be. 100% liquid into the TXV. That's what sub cooling is!

Techman

sg again

You said so ! in a backwards way ! You had to add "extra" and "not needed"  Freon to clear up the SG , so w/o that "extra" Freon the  refrigerant condition was "saturation". Feeding the TXV with the same stuff.       The Freon levels in both systems - with & w/o a SG - would the same by adding the 9lb 1oz. charge. With the SG ,I get to see the not quiet full LL. So not full at the SG gives the TXV a not full LL .

Spence

SC

I am just as much against overcharging as undercharging; hence, my reliance on manufacturer's prescribed methods and nomos in the unit. Overcharging does not create saturation. Overcharging creates overcharging. Saturated refrigerant is what you see on your manifold gauges. In its purest form, saturated means adding heat changes liquid to vapor; taking away heat changes vapor to liquid. That is why the actual liquid line temperature must always be colder than its saturated temperature, which you see as pressure on your manifold and then convert to temperature. A classic example of this is Ingersol Rand; after the last circuit through the condenser coil, you will find an extra pass of tubing upstream of the LLD and service valve. This is a "sub cooling loop." The thought process is that if the refrigerant is allowed to stay in the ambient just a little longer, then the extra time is assurance that as much superheated vapor has been condensed as possible and feeding the TXV with only liquid. That overcharge has to go somewhere, so it will stack in the condenser. Since the condenser must be exactly that, and not a receiver, then the resultant capacity loss from the OD coil not being allowed to do its job is a risk not worth taking.

Techman

SG again

Our gauges  (PT Chart ) are only good for use w/ saturated conditions in the evap and cond coils. Vapor and liquid/droplets side by side, just like the saturated conditions in a Freon drum and in a receiver tank. For shame here, lets forget about SG's for a short minute  OK . What does your mfrg of choice have to say about having a "full" LL  or an "almost full" LL for/at  the TXV? What does the mfrg of the TXV that's in the evap that's in your mfrg of choice unit have  to say?

A SG is just that! Its is NOT a charging device.

Find out from your mfrg of choice,just how many of the bottom passes of the cond coil are reserved for liquid Freon. 2-3-4?

Under normal operating conditions the TXV cycles between opening and closing all the time, in order  to maintain a full LL at the TXV extra Freon has to come from somewhere and then go to somewhere as the TXV cycles closed. That sure mimics the purpose of an actual receiver tank.

That "subcooling loop" has been around for a long long time.That loop is for liquid Freon only, no condensing ,no superheat.

Techman

Oh yea,ICOR (HOTSHOT) says

that the slide they showed at the refrigerant class ,the slide picture that showed  a SG w/ an x thru it  and the wording "do not charge to a full SG"  was meant for "initial pull down "only ! Just like normal I think. They cautioned about mistaking an errant bubble or even a sudden flashing and disappearing of flashing as being low on HotShot.That applies to most of the "blended refrigerants"