Refrigeration question

[rsp4834]

I have a question for you guys concerning refrigeration systems. I am a H.V.A.C guy who is expanding into the refrigeration side of the business. I have a customer with an open refrigerated meat display case. They have been having problems with the system staying in the defrost mode. I have found out it has a bad defrost timer. The contacts seem to be stuck together. My real problem is I don't know for certain what refrigerant this system has. It has a semi-hermetic Copeland Compressor in it and I see more action in the sight glass than I would consider normal. since the evaporator coil was totally froze up I decided to shut everything down before going any farther. I took all the panels from inside out to get to the coil and I found the TXV is for an R-22 system. Is it common practice to have R-22 in a refrigeration system? How can I tell what refrigerant is in the system. There are no markings indicating Refrigerant type.I recall that you can tell if its R-12 by seeing what the pressure is with the system off and compare that to the ambient temp. ( IE 70psi would show at an ambient of 70 deg.) This may only apply to an unmarked drum of refrigerant. Any help you guys can give is appreciated.

[dorrmann]

If the TXV is for R22, I'd say that it's a pretty safe assumption that there is 22 in the system. Of course, even in my own experience, there are exceptions. (http://hvac-talk.com/vbb/showthread.php?threadid=77727) Look both in the case and on the condensing unit for a tag with the refrigerant charge on it. It's bound to be there somewhere. Worse comes to worse, call the local distributor for the compressor and ask them. They should be able to tell you what refrigerant that compressor was made to be used with.

[rsp4834]

Thanks dorrmann! I will have to check around the condenser for a tag. It seems to be a practice in my area to "pop" the tags off so the next service guy is in the dark.

[techstructor]

This can be a sticky issue but there are a couple of things you can try. First of all remember that you can't go by the name plate on anything, you can only assume (or ass-u-me as the wise old sages say). Like you yourself said, you can figure out what type of refrigerant you have by going back to your saturation P/T chart using the ambient air as the reference temperature. For instance if it is R-22, at 70 degrees F you should get 121.5 p.s.i.g. However, some factors you must consider which will give a false pressure reading, could there be a mixture of 2 or more refrigerants? Could there be non-condensable gas in the system? Now, If you do this you need to have the system off for several hours before trying to determine the exact pressure/temperature and remember also to open your pumpdown solenoid valve if it has one so you equalize both sides of the system. Next you will want to use the temperature on the coolest side of the system (condenser or evaporator) because that is where the liquid will settle. Now make sure that your manifold gauge is accurate by calibrating with a cylinder of virgin refrigerant, then take the pressure reading on your system. Once you are comfortable that you have a good reading, start the unit and measure your high pressure and compare this reading with the ambient plus 30 degree rule and see if you are still looking at the same refrigerant. If ANYTHING looks out of whack, recover the charge and evacute the system to 500 microns and then weigh in a virgin charge of R-22, then test the system. As for the refrigerant that you recovered, many supply houses can test refrigerant for A.R.I. purity which will at least let you know what came out of the system. Good luck my friend!

[hiltontech]

Very good advice techstructor

[Yuma]

Originally posted by techstructor
Once you are comfortable that you have a good reading, start the unit and measure your high pressure and compare this reading with the ambient plus 30 degree rule and see if you are still looking at the same refrigerant.
NOT ALWAYS!!!!!
I have talked to companies that design in only 15°f TD on condensers (and seen it!).
The ambient plus 30 rule is only for older A/C systems. Now all that 30+ rule is changing (Even in A/C's).

The idea and thought is good, but if the TXV says R-22 than that's what should be in it. If in doubt, Pull it out! ......
And put fresh gas in. Refrigeration is a little different cat. :)

Yuma,

[rsp4834]

OK, here's the latest developement of this on going fiasco. Did a T/P check and it looks like the system has R-12 in it. I called the compressor dealer and had them do a check and they came back with R-12 as the refrigerant for that compressor. Why in the name of all things holy did someone put an R-22 TXV in this system? I think now would be a great time to change over to a new Refrigerant. I used R409A on another R-12 change out and it worked fine. guys, thanks again for your assistance! Now if I can figure out what superheat to set the TXV at and whether I should use an R-12 valve?

[pecmsg]

Get A R-12/R-134A X-Valve and install it. Change your gas to 409A or Hot Shot what ever you like. I like Hot Shot.
R-134A has gotten to costly.


"Why in the name of all things holy did someone put an R-22 TXV in this system?"

#@it happens at least you checked and found that the compressor will not handle the higher pressure of R-22. The damage is done. let the customer know.

[R12rules]

You asked how to know what superheat to set the new TX valve at.

What are you talking about?

TX valves do that all by themselves! In fact .... it is the ONLY THING they do!


Give them the refrigerant they are designed to feed ...
Give it to them with the correct temperature and add just a little sub-cooling for good behavior ....
Give it to em' clean and dry and they wont make a fuss.

Valves dont need much attention, once the system is operating properly.

Guys tend to harp on the TX valve whenever they feel they dont get the cooling results they expect.


Now of course there are times when making an adjustment to the TX valve is necessary.
Like when the last guy who was there didnt know his his head from a hole in the ground and fiddled around with the adjustment stem for hours on end ....hoping to feed more or less refrigerant when all the while he had a plugged drier, dirty condensor and or a clogged inlet strainer @ the TX valve itself.


Another mis-nomer about TX vlaves is that they often go bad.
When for the most part ....they hardly ever fail.
The inlet strainer gets pluged and restricts the flow of refrigerant to the valve ... ... and guys will begin by screwing the stem to feed more refrigerant in while they SHOULD be checking the screen!!!


And when you find a valve that is dead ... nothing is feeding thru it .... it is more than likely just the power head which is bad.

Pump er down, clean the inlet screen and replace the power head. Change the liquid line filter drier, open the king valve and let the refrigerant do it's job.
Before you know it your down the road.... smiling all the way to the next service call. :)

[forged alloy]

9 out of 10 TXV's I see condemned by field tech's upon examination are simply plugged by residue from improper brazing techniques. Sporlan ships em out clean as a whistle! Always braze with a breath of nitro and you'll prevent mucho headaches for yourself, or those picking up the pieces. This residue blows right by screens and lands on the pushrods and needle valves.

[rayr]

Originally posted by R12rules


Pump er down, clean the inlet screen and replace the power head. Change the liquid line filter drier, open the king valve and let the refrigerant do it's job.
Before you know it your down the road.... smiling all the way to the next service call. :)

TSK, TSK, TSK!! How about maybeeee just a little evacuation???? 30" would be good (lol) Had a (ahem) collegue tell me one time that he always evacuated to 31". My response was "Hmmmmm, not on this planet"

[rsp4834]

Thanks for the input R12rules, but most TXV's are sent from the factory set for 6 deg. superheat according to what I was told once by ALCO. This may or may not be adequate for this application. I don't actually have a problem with a the TXV, I have a problem as to why an R-22 valve is in an R-12 system in the first place!

[txguy]

ALCO does set MOST tx valves at 6 degrees superheat, and most times that is close enough for general purposes. Understand that the 6 degrees is a static setting. In other words, where the metering pin clears the seat in the valve by .002 inches. Total stroke, or working superheat, depending on valve could be as much as .028 on balanced port and .050 on conventional. The actual superheat that you will show is dependant on the quality of the liquid, (how much subcooling), the pressure drop across the valve, and the port size in relation to the actual tonnage required.

Best thing is to get the system up and running and do a superheat check during pulldown to avoid floodback, and just before the load is satisfied to set working superheat. This will give you an indication that the valve is operating properly.

In general terms A/C systems will require around 10-12 degrees superheat, medium temp between 8-10, and low temp between 6-8, AT THE EVAPORATOR. And this changes from manuf. to manuf.

All this is meaningless though, as the reason for superheat in the first place is to keep the compressor alive. Look for 20-25 degrees superheat at 6 inches back from the suction service valve.

Also, make sure that the R-22 that you are reading is from the power head of the valve and not the valve body. Power head changes are common these days to make a valve that was originally one refrigerant and tonnage into another refrigerant and tonnage. A 1 ton R-22 body with an R-12 head is now a 1/2 ton R-12 valve.

[rsp4834]

Thanks TXGUY! Yes, the power head on the valve is R-22. i was trying to find a tonnage on the powerhead. The numbers i get are .....C 2/1 1 EVG. This is as close as i can get reading upside down and backwards!! Any Clues?

[Yuma]

The valve information is stamped on the side of the body. At times they are hard to find and read but it is there.

Yuma,

[txguy]

That is a Sporlan GVE 1 1/2 C. It is a 1 1/2 ton R-22 medium temp G body with external equalizer.

[rsp4834]

Right you are! i told you upside down and back wards and no glasses!!! lol thanks for cracking the code!!!