Measuring Superheat on a Carlyle 06D system

[747ken]

I'm working on a transport a/c system using R22 and a Carlyle 06D compressor.

To measure the superheat, the maintenance manual tells us to place the temp probe next to the TXV's temp bulb.
That's easier said than done, because that area is very hard to get to (only one hand can fit in there). In addition, the TXV's temp bulb is covered with several layers of insulating tape, which can't be removed without destroying it, due to the strong glue.

So I need another place to position the temp probe. Some textbooks say on the suction line, 6 inches from the compressor. This would work, but its about 6 to 7 feet away from where the manufacture says to place the probe. I don't know how this would affect the superheat reading (the manual's superheat range is 12 - 18 degrees, with 15 being ideal). Is there a conversion factor I need to use, to compensate for the excess length?

[Jabarco]

In that case, I would use the instructions "on the suction line, 6 inches from the compressor". Ideally, 20 to 30°F of superheat is what you want at this location.

http://i199.photobucket.com/albums/aa214/jabarco/dork2.jpg

Jabs

[skpkey9]

Bingo:D

[supertek65]

yes, make sure that you are fully loaded and check 6" away from the compressor and 25 degrees is great!

If you are checking at the tev sensing bulb you should have 12 degrees.

Of course the vapor refrigerant will pick up additional superheat through friction as the refrigerant passes through all those turns and fittings on its way back to the compressor, it might even pick up a little solar gain depending how well insulated the suction line is.
Then if the compressor is outside on a hot day, with condenser fans pulling 100 degree air across the suction line you might have picked up some more superheat.

now your 12 degrees of evaporator superheat is 25 degrees compressor superheat. maybe 30.
I like 25-30, I hate changing compressors due to liquid flood back and it is scientifically proven that refrigerant vapor contains liquid at 9 degrees superheat.
good luck
Frank

[chad_nc]

yes, make sure that you are fully loaded and check 6" away from the compressor and 25 degrees is great!

If you are checking at the tev sensing bulb you should have 12 degrees.

Of course the vapor refrigerant will pick up additional superheat through friction as the refrigerant passes through all those turns and fittings on its way back to the compressor, it might even pick up a little solar gain depending how well insulated the suction line is.
Then if the compressor is outside on a hot day, with condenser fans pulling 100 degree air across the suction line you might have picked up some more superheat.

now your 12 degrees of evaporator superheat is 25 degrees compressor superheat. maybe 30.
I like 25-30, I hate changing compressors due to liquid flood back and it is scientifically proven that refrigerant vapor contains liquid at 9 degrees superheat.
good luck
Frank



Where did you get your info on refrigerant vapor contains liquid at 9 degrees superheat, I have never heard this before.

[supertek65]

John Clark C.M.
John Clark is from compressor manufacturers of America, or something like that!
He wrote the compressor section in the RSES SAM manuals.
I think he and Wes Taylor the chief engineer from Carlyle are the two big compressor gurus in the country.
I think John is a very reliable source.
Frank

[consolidmech]

Never heard of that statement " superheat at 9 F contains liquid". The Carrier 30RB chillers with EXVs run on 7.5 to 8 f superheatentering the compressor. These are design conditions. In that case all scroll compressors would have to be replaced under warranty.

[will 2]

Friction ?

[hands]

I'm working on a transport a/c system using R22 and a Carlyle 06D compressor.

To measure the superheat, the maintenance manual tells us to place the temp probe next to the TXV's temp bulb.
That's easier said than done, because that area is very hard to get to (only one hand can fit in there). In addition, the TXV's temp bulb is covered with several layers of insulating tape, which can't be removed without destroying it, due to the strong glue.

So I need another place to position the temp probe. Some textbooks say on the suction line, 6 inches from the compressor. This would work, but its about 6 to 7 feet away from where the manufacture says to place the probe. I don't know how this would affect the superheat reading (the manual's superheat range is 12 - 18 degrees, with 15 being ideal). Is there a conversion factor I need to use, to compensate for the excess length?
What I do is make a small cut in the insulation by the TXV bulb to get the line temperature, then cover the cut with foam tape. As far as the difference in line temperatures at the bulb or at the compressor, I have checked at both areas on the same unit with about 7 to 8 feet of well insulated pipe between the two points and only had about 1 degree difference in temperature. But this is on a chiller where the compressor is in the same room as the evaporator.

[747ken]

What I do is make a small cut in the insulation by the TXV bulb to get the line temperature, then cover the cut with foam tape.

That's also a good idea. I'll have to get another temp probe besides my Fluke pipe-clamp type.

Also, I came across this superheat kit. It might work since my system has a schrader valve right next to the TXV's temp bulb. Anyone use one of these?

http://www.cdvalve.com/products.asp

[A-Tech]

You can find everything you need to know about the superheat at the following link.
http://www.brainerdcompressor.com/superheat.htm

Hope this helps!

[jogas]

yes, make sure that you are fully loaded and check 6" away from the compressor and 25 degrees is great!

If you are checking at the tev sensing bulb you should have 12 degrees.

Of course the vapor refrigerant will pick up additional superheat through friction as the refrigerant passes through all those turns and fittings on its way back to the compressor, it might even pick up a little solar gain depending how well insulated the suction line is.
Then if the compressor is outside on a hot day, with condenser fans pulling 100 degree air across the suction line you might have picked up some more superheat.

now your 12 degrees of evaporator superheat is 25 degrees compressor superheat. maybe 30.
I like 25-30, I hate changing compressors due to liquid flood back and it is scientifically proven that refrigerant vapor contains liquid at 9 degrees superheat.
good luck
Frank

Frank, are you implying that the refrigerant will absorb 13 degrees (25-12) of superheat while traveling thru a "6-7 foot" suction line? I think this is highly unlikely unless that line is running thru a very high ambient.
jogas

[onetime]

The txv companies say there can be liquid droplets in the suction line at superheats up to 6F.

[747ken]

You can find everything you need to know about the superheat at the following link.
http://www.brainerdcompressor.com/superheat.htm

Hope this helps!

Yes, some good information. Thanks

[supertek65]

Jogas,
no I am not implying that it will pick up the superheat in any amount of time or distance, only that a vapor refrigerant at 9 deg compressor superheat has some liquid in it.

I have seen on low temp splits that if you measure the suction line 10 feet from the compressor and then at the compressor on a hot day over 90. I believe due to the hot air passing over the suction line "usually not insulated" 13 degrees difference.
That by the way is on my own personal walk-in.
I did do something a bit odd!
I re-piped my condensate drain from the walk-in on top of my compressor outside. It is in a very hot corner of the building.
Maybe I should run it over the liquid line to increase my net refrigerant affect.

Frank