Walk-in freezer charging
I am new to this site as well as fairly new to the refrigeration repair end of the business. have done HVAC for a number of years as well as some refrigeration work. Took a new job with a local school district and have been thrust into the refrigeration world.
We have a walk-in freezer (404A) small unit box is 6'x6' that recently had the TXV changed by the former tech. Only about 8' of piping between cond and evap. Unit came down to temp initially but then lost some refrigerant and quit working. Enter Tom in the picture.I did some intial testing and found a leak on a service valve as well as a leak in the piping. pressure tested and evacuated the system down to 500 microns. System appeared to 1st hold pressure for 2 hours as well as the vacuum for a couple of hours. Charged the system yesterday with aprox. 6# 404A as well as about 1 oz. flourescent dye. Site glass was fulland clear
Box came down to temp overnite and when I checked this morning box was at about +9 and operating just fine. Checked for any sign of leaks and saw none with the UV lite. Had a compressor to put in and did not get back today but my boss was by and said there were bubbles (flashing?) in the site glass.
We are in 100 degree temps in MO and the box was well over 90 inside when I initially charged it yesterday. There may be a leak I have not found but I did a pretty thorough check at at this point if it is aleak it must be in one of the coils where I have yet to see it. After all this the question I want to ask at this point is: Is it possible that the system may need additional refrigerant after it reached operating temp. Could the site glass give a "false" reading due to the high temps in the box? TXV seems to be working OK and I was waiting to tweak the superheat when it was down to operating temps.
Thanks in advance for your input. I am enjoying the challenge but this one has me somewhat stumped.
I assume it has a receiver, tank in the liquid line right after cond? Don't be offended if you know that, you said you were just getting into this side of business. With a receiver a full glass does not mean a full charge, especially when ambient is very hot. In fact it is going to be significantly under charged. With ambient above 65-70, from a vaccume charge to a full glass plus about 20%. That will get you close. May need a little more when ambient drops below 65-70. You may have a leak if your ambient has not dropped but sounds like you were pretty thorough on that. Give it another 1-2 lbs of 404A and let it eat. Let it pull down to zero and get on that SH, 6-10 at the bulb should do. Good luck
Thanks for the reply. Yes it has a receiver as well as an accumulater on the suction side. I am a newby so no offense taken!!! I will add additional refrigerant and see what happens. Could the conditions I described cause it to appear "full" in the site glass at start-up then show bubbles 36 hours later after running?.
Thanks again for the help
[QUOTE=tomnkc;13898741] Could the conditions I described cause it to appear "full" in the site glass at start-up then show bubbles 36 hours later after running?.
It may not have taken 36 hours to show bubbles. How long did you stick around after you filled it ?
Check the TXV to see if it a pressure limiting type. If yes, you charged the system when the box was hot and the TXV was throttling flow to keep the evaporator pressure from going too high and overloading the compressor. Later on, when the box was cooled down, the TXV flow would increase flow and need more refrigerant to fill the evaporator coil and try to reach the valve's superheat setting. Pressure limiting TXV's are very common on freezer systems.
I was around about an hour after initial charge yesterday and then back about 7am today. No bubbles showing this morning. Bubbles were present about 2pm today according to my supervisor.
Now the newby will really show. How do I tell if it is a pressure limiting TXV?
[QUOTE=tomnkc;13899501 How do I tell if it is a pressure limiting TXV?[/QUOTE]
Look on the power element label. It's on the disk like gizmo, it has a capillary line with a sensing bulb attached to it.
I can tell you that if you held a good vacuum for several hours (!), that you have no leak. :cheers:
I would use the fluor. dye as a absolute last resort, always. As in, when you cannot find the leak with other equipment. Which you should always be able to do with a good detector :grin2:
Pressure limiting will be indicated on the TXV label. For example- your valve might be a SPORLAN EFSE-1-SZP. The Z = low temp amd the P = pressure limliting. On some applications there will be a number after the P indicating the highest pressure the valve will go. You can Google Sporlan literature then download brochures about their products. If you're going to do refrigeration work, you need to know Bulleltins 10-9 and 10-10 by heart. Alco valves will have a Z for low temp or a W with a number if a pressure limiting type. The number is the MOP [maximum operating pressure]. So you could have an Alco AFAE-1-SW45. I'm not real familiar with Danfoss valves but I believe they will indicate the MOP on the label, like MOPxx.
Does the system have a head master? Youll need to account for that when charging too.
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Again the newby will show here but I believe it does have a headmaster based on what I have learned on here so far. Is the headmaster a device that sits between the receiver and the condenser and looks like a diaphram with a cap tube coming out of it?
I read alittle about charging with a headmaster installed but will need to reread it to try and understand.
I can't Thank everybody enough for the help. Maybe Someday i will be able to pay it forward
Originally Posted by tomnkc
Yes that is the headmaster. It is as the name says, master of the head pressure. During low ambient it will stack liquid in the cond, from the receiver, to keep the head up where it needs to be to operate properly. During high ambient that extra refrigerant is stored in the receiver. So you need X amount of refrigerant to cool when it's hot and Y amount when it's cold.