Txv Superheat

[tempdelta]

Anyone know the actual correct way to set / check the superheat on a txv.. Say low temp R-22
13 psi -20 sat A range of -10 deg (valve open) +5 deg valve closed. Discharge air -4.0 (open valve) Can someone actually explain the proper procedure (not the obvious) line temp/sat/psi.. I'm not understanding where the fixed superheat is when the valve hunts.. I know alot of guys if the case isn't getting cold enough, they just open the valve. Which isn't good losing effiency + getting floodback to rack... I understand what superheat is, but damn do I have a hard time getting it accurate.. Any help would be appreciated.. thank you...

[markettech]

I'm not the sharpest tool in the shed but superheat isn't exactly rocket science. I think the real key here is to find out why the valve is hunting. 15F temp swing seems like alot. Valve sized right? Liquid getting to case? Postition of the sensing bulb. That's the kinda stuff I would start looking for.

[tempdelta]

so your saying there shouldn't be a temp swing? it should remain constant is my question.. reason being.. I actually check the ****.. and spend alot of time doing it also..

[markettech]

I spend quite a bit of time on superheats also - don't think there is any quick way to do it. Spent 6 hours setting superheats on 2 circuits last week (had plenty of filler work if you know what I mean).

Inevitably there will be a certain amount of temp swing - no gettin around that. 15F just seems like alot is all.

I typically use my Fluke 52 with clamp on sensor and average the temp over {x} amount of time. If I make an adjustment I usually give it 15 min. or so to settle out.

[innovator]

You probably already checked, but I have found plugged screens to cause oil fails trips, hunting etc.... just my 2 cents

[tempdelta]

right, I use my cooper.. one probe discharge, one at bulb.. I also allow 15 min per adj.. however I'm trying to pick up more mrkts for the company, my theory of that is to educate the customer about "superheat" If I can convince them that a full mth bi yearly pm could save them 20-30 grand on there electric bill, repairs, and loss of compressors. I think I've got a good stand on it.. However most markets I service seems like there is not ONE txv set properly.. I've seen Suction/liquid lines almost crimped at the txv and has been running that way for yrs.. where is the superheat and oil return on those cases? I've always got them close.. just was always told txv maintains a constant fixed superheat.. which it does.. but man it takes forever to actually set one properly specially if the valve is wide open and the power cap is bad.. From some previous EXPERT technichian.. mths b4 I get the call.. ya know?..

[gerryboy00]

http://www.sporlan.com/10-143.pdf

[markettech]

If you want to sell the customer (if their big enough) - explain the benefits of installing an E2 on their racks. Get sensors installed in the cases. Install a PMAC panel. Hook up an IRLDS. Big investment, but will reap huge rewards for the customer (and you) in time.

[innovator]

Also, superheat is directly affected by subcooling temp, most especially R-22 low temp, so if you want a tighter temp (say 8 degrees or so) see what the subcooled liq temp is, if there is any...

[thegoodhumorman]

depends on what the fixture is you are servicing as to what is a proper superheat- typical ranges.
tub IC 3-5*
tub FF 4-6*
RIFF 6-8*
MD 6-8*
W/I 10-14

Rarely have I seen a valve flat line unless it is undersized.
Great guy who passed on a couple years back used to set everything on sales floor at 6*. Would drop it to 5* on Ice cream.

Innovator correct on subcooling- if its on your rack it needs to be working to set SH properly.
Subcooling to 50 deg adds an incredible amount of capacity to a rack system- many systems so tight cannot work without it.
Redundancy? Dammit Jim I'm an engineer not a friggin dictionary....!

[tempdelta]

Most stores I service cannot afford an E2.. Speaking of the e2, everyone know how to commission a td3? ;) man they are fun...

Thanks for the support on Txv supheat...

[markettech]

Not suprised that most superheats in the stores are off. We run into the same thing when taking over a store.

If technology isn't the answer, then I would push hard for a maintenance contract as well.

A little money spent well now will save them alot later.

[tempdelta]

we already have a pm contract.. which consisits of leak check control safety check operational pressure / net oil defrost..

It does not include going to each case exposing electrical checking wiring / connections ... superheats excedure.. the **** that matters they dont want...

[jumperwire]

to lower superheat means that more refrig is needed in the evap.

with more refrigerant the point at which all vapor is boiled off moves closer to the coil outlet. in other words, more of the evap is filled with refrig.
the difference is less between (1) the point it is all boiled off and (2) the temperature at the bulb. this is the superheat.
the evap temp remains the same (40 degree.) its just the outlet temperature at the bulb that is lower ( 46 degree. ) than it was before ( 50 degree. )
on sporlan valves rule of thumb for changing superheat is : one turn of the adjustment stem changes superheat 4 degree.
therefore one turn should be about right
in this expample , turning the adjuster back counter- clockwise lowers the closing pressure on the needle. this allows more refrig. into the evap, lowering superheat. i heard superheat r-22 superheat at the evap outlet should be 6-8 degree ?

[markettech]

Boy, the only thing I can suggest there is to kinda pick away at it. Suggest to the manager/owner that high or low superheats cost him $$ (haven't seen one yet that doesn't want to lower operating costs). Ask to check a couple of circuits each time you're in doing the maintenance. Over time you'll be set.