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walk in freezing up?

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scrmndmn

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Discussion starter · #1 ·
I ran into a walk in fridge that has froze up and hope someone will help? I think the TXV isnt adjusted correctly, but need another oppinion.
ODT is 63* and indoor is 38* with 49 & 190psig with a 22* suct temp & a 93* liq temp.
From what I was told liq. sat. temp should be amdiant + 30* with 10* subcooling, and superheat should run 20-25*.
Please let me know if this is wrong and help me learn the right way to charge these walk ins, Im used to res. and light commercial. Thanks in advance.
 
#8 ·
10 degree sc sounds fine, but check sh at evap, that will get u in ballpark , also be a detective , it could be as simple as a door being left open over night and never being able to rid of frost , this is quite common, 10-12 deg supheat at coil regards stan
 
#12 ·
This is a refrigeration system, not an A/C system. You charge it initially by the sightglass and if it has a condenser flooding control like a Headmaster you need add more to account for that per the manufacturer's charts or by calculation of condenser volume vs. minimum ambient temperature.

Forget about liquid subcooling to charge these things. Your LSC won't change a wit until the receiver is full and the refrigerant starts to stack up in the condenser coil.

As for the suction superheat, you want about 10ºF at the outlet of the evaporator, but more importantly you need to keep the compressor SH between 20ºF and 40ºF.

Heatcraft has an excellent I&O manual that get into this quite thoroughly. Check it out.

I have to run, maybe somebody else will post a link to that one. ;)
 
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Discussion starter · #13 ·
thanks icemeister.I have no literature on these units, so Im triing to find out how to properly charge and check the charges in these systems. Should the cond sat. temp = ambiant + 30*.

Your right these are not A/C systems. Thanks Again.
 
#14 ·
I'm back.

Here's the Heatcraft Link:
http://www.heatcraftrpd.com/resources/install/H-IM-64L.pdf

That ambient plus 30 rule is an old A/C guideline......forget that one too.

In a commercial refrigeration system the saturated discharge temperature is relatively fixed by its design, the load and the ambient temperature. You can't raise or lower it by adding or removing refrigerant because the receiver is there to compensate for system load and ambient fluctuations. The saturated discharge temperature you get is what you get.

The same goes for liquid subcooling. Adding refrigerant to a system with a receiver will not increase the LSC leaving the condenser unless the receiver is full and liquid is stacking up in the condenser.......which means that you're seriously overcharged and should be shot. ;).........Otherwise, whatever subcooling you get is all you're going to get.

[Edited by icemeister on 06-05-2006 at 10:08 PM]
 
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#16 ·
im back too, thats right Ice and thats the reason we use suction to liquid subcoolers in dx systems scrmndmn and other types of heat exchangers , preventing flashing before valves and allowing particular condenser controls to do their jobs, Txv counterclockwise reduce superheat and vice versa like any valve
clock wise usually reduces flow ;)

now does anyone have the link to copelands refrigeration manual? im on emerson but cant find it, i would like to browse thru it myself
thanks stan
 
#17 ·
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Discussion starter · #18 ·
What Im triing to figure out is how to tell when I adjust froen charge vs. adjusting the TXV, (knowing it has been adjusted before ), and what to look for pres. temps.etc.
Isnt there a way to determine what the head pres. should be. Sorry for all the questions and this info from you two is wonderfull. Thanks again.
 
#19 ·
If the TEV is totally messed up as you suspect, first count the number of turns of the superheat adjustment stem form full closed to full open and set it halfway. That will get you somewhere close to a factory setting.

Then charge the system to a full sightglass and check your superheat at the evaporator outlet (near the sensing bulb) when the box is close to design temperature. You should shoot for around 8-10ºF superheat. Then check the compressor superheat (at about 6" from the suction service valve) to insure that you're within 20ºF-40ºF superheat as recommended by the compressor manufacturers. If you're outside those limits, readjust the TEV accordingly regardless of what you have at the evaporator outlet.

Don't be overly concerned with what your pressures should be because that's more a function of the system design, ambient conditions and box temperature......not something you can adjust by playing with the charge, TEV and such. As I said earlier, you get what you get.

 
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