Answer is... it depends. The thing with refrigeration is they are all different. Quite rare to see a self contained reach in without a nameplate refrigerant charge, too. If it is custom with remote condensing unit with receiver, then charge like a normal refrigeration condensing unit. Anything self contained I weigh in charge.

What is correct superheat? Dunno. Few manufacturers even have documentation of what it should be. Where are you measuring? At evap or compressor? Does it have heat exchanger? Cap tube or TXV? Low temp, medium temp? Compressor running just one evap, multiple evaps or evap + cold rail? Is cabinet temp already within 5 or 10f of setpoint? Is condenser clean? All these things will greatly affect superheat, so its difficult to use superheat as a reliable charging method. Its helpful for diagnostics, good idea to check a lot of things and familiarize yourself. For charging though, weigh it in whenever possible.

 

What is proper SH? I like trippintl0 response.
10*evap SH is pretty close, depending. Slightly more important is Total SH 6'' before the comp which is 20-40*F ,depending.
Now, depending on how good you want to be I suggest you get your hands on Dick Wirz book 'Commercial Refrigeration for Air Conditioning Technicians'.

It is a Good Read, and an even better re-read.

 

Yeah, I ordered that book on eBay, should be here next week

I just hope I can understand it. I have very poor reading comprehension. I never got through high school. Just started being a residential HVAC helper since I was 16 and.never looked back

 

I moved your thread to the “Refrigeration and Ice Making” forum.

You should get the most responses to your question in this forum.

Please take note of this new location.

 

Plug the condensing unit in without the evap fans.
Get a frost line to the pump and back it off a few inches.

 

Plug the condensing unit in without the evap fans.
Get a frost line to the pump and back it off a few inches.

Now that is an OG interesting way to see stuff
Thanks, may just try that in shop with mock up to see if it holds true
The other field "OG fix is Delta monitor, and careful addition of freon with a liquid-to-vapor nozzle.
Some old R12 cap units are still chuggin along, using COLD SHOT2, and built like the Eiffel Tower
(ALSO, in Commercial kitchens,use a tool tray, because cooks seldom look where they walk,and your tools/parts WILL get kicked around- - -OG Wisdom, learned the hard way)

 

"I think the work will be easier, but it'll be more complicated."
Why would you think this? Get ready to work in greasy kitchens, have food dropping on you. And maybe, depending on you, never eating out again because you've seen the kitchen 😱😱

 

It's a maintenance job. Most guys here are sitting around most of the time, waiting for something to break

And we will fix things before the kitchens open. If there's an issue the back shift guys cant fix, they just note it in the log book and we come in early, read the book, and take care of the notes

I will be coming in at 4am every day

 

It's given me a nice 50 year run with more to go.

 

Never liked working on the hot side in kitchens.

 

If there a good customer and wine and dine me I dont mind taking a look

 

So, What facility is this?

Union?

 

So, What facility is this?

Union?

Yeah Local 501
Its a giant hotel casino in las vegas

We even have our own elevator mechanics

We got a guy, the ONLY thing he does is certify backflow preventors.

 

Welcome Brother
IUOE Local 30 NYC Retired

 

Someone just told me match box temp plus 10

 

For what?

 

Someone just told me match box temp plus 10

suction saturation temp 10 degrees lower than your box temp

Plus ten, minus ten, meh, it's all the same.

What if that results in zero degrees superheat? Just asking for a friend . . .

LOL

 

My biggest problem is my reading comprehension is terrible and im also terrible at explaining things

 

You just explained what you need to work on. One nice thing, compared to so many other things in life, is that it doesn't cost much if any money. But that's what we do to better ourselves in life, we work on our weak points. Maybe make a point of reading this forum 15 minutes in both the morning and evening, or it could be a book that has nothing to do with our trade, everyday.

One kinda sorta funny thing is you may not even notice that you are improving, because you are your own worst critic, but you will improve.

 

Your SH on static, gravity coils, and cold rails about 2*. 6-8* on a freezer fan coils and 8-10* on cooler fan coils (no different than walk ins)...and when you realize that the difficulty in getting a SH reading from a unit that small is damn near impossible, you'll listen to @pecmsg

The above numbers are for evaporator SH not compressor. Due to the short runs, there shouldn't be much difference between the 2.

 

replying to follow thread,
ty

 

I got the book. Time to start reading. Wish me luck.

 

Congrats!!!!!!!!!!!!!!!
Now all you have to do is read,get confused,come here,re-read and start to get some good comprehension.

 

If it's just an "add gas to see what happens" situation, I'll shoot for the saturated evaporator temperature to be 25 below box temp and monitor performance. Nicer equipment tends to have a lower TD, like 20 degrees. There's basically zero point to looking at superheat in a cap tube system because of the heat exchange between cap tube and suction line.

Weigh the charge in after an actual repair, though.

 

Still need to know Total SH 6'' before the comp. And that is 20-40*F SH.

 

I hope this book isn't too old. It's 2nd edition, sold by Goodwill on eBay. I don't think much as changed since then.

 

For me I'm not sure that I have ever encountered an OEM TD of 25*F. Most WIR/WIF are 10*F TD. Some RIR /RIF are closer to 15* TD and lots of RIR/ RIF are around a 20*F TD.

One of my many 'pet peeves' is that the OEM nametag should have the OEM TD .This is for all self contained WI/RI/under counter units. It is just another # in figuring out how a unit is running

 

Principals haven’t changed.
Receiver? Flooded head pressure control… If sized properly it should be 80-90% full on hottest summer day and 0-10% full on coldest winter day.
should have some means of subcooling the liquid supply to the txv, elevation, liquid/ suction xchanger, subcooler circuit….

 

I've got the reach in blues. 10 years ago I'd be replacing compressors, cap tubes, evaporator coils, etc....

Now I give them a price for repair and they just go with a new cheap box instead. Can't blame them.

My knees are happier with that outcome, I suppose.

 

Have you seen the replacement cost with R-290?

 

I'll chime in...
I've charged hundreds of reach-ins coolers, hell it might be over a thousand by now.
Put a line tap on the suction stub, find the total charge amount.
Put your 134a cylinder upright on a scale and charge to 20 psig not exceeding total charge amount.
If you can't bring the suction up you've got a restriction typically the cap tube or drier.
If it last a year you're golden in the customers eyes.
If it's flat in short order you should be able to find that leak and 80% of the time it's in the evaporator coil.

Still cost affective for the customer to replace the cap tube and drier vs purchasing a new R290 cooler.
Those are completely junk and leak out within 3 years no matter which manufacturer you choose.

 

Wish me luck 🤞🏻
I'm off to service a chef base and find a leak in the work top cooler across from it that I gased last week 😁

 

Come back and let us know how it went!!

 

Good Luck . . . !!