walk-in cooler evap frozen top half only

[nighthawk]

I have a walk-in cooler. I just replaced evap coil with identical unit 7000 btu bohn coil new txv as well super heat set at about 18. Works great for a bit then over night the coil freezes up bu the top half only I'm thinking faulty txv but just want to be sure

[mcunliffe4]

You could try opening the valve and monitor the superheat, also woth checking the orifice is not undersized

[Gary]

... new txv as well super heat set at about 18.

What does this mean?

We could assume that you measured the superheat (?) at the TXV bulb (?) with the refrigerated space down to design temp (?) and the superheat was 18'F (?)... but why should we have to assume anything?

We can't see the system from here. You have to describe it to us.

[nighthawk]

I put a new txv in when I replaced the coil and set superheat at 18 degrees.

[Gary]

Why did you set it at 18'F?

[Contactor]

Did you replace the TVX and orifice with the same type and in the same position?

Why did you change the indoor unit?

What refrigerant is the system running on and what is the set point?

What are the defrost arrangements?

[gas bottle]

Why did you set it at 18'F?
That superheat looks pretty high - I would normally design at 6ºC (10-11ºF). The coil appears starved to me. Did you set it up correctly ie pressure at coil outlet compared with the temperature at the phial?

[Contactor]

How is the expansion valve equalised and where is the phial located?

[indian]

I was thinking from a different view point how does the coil defrost. If just the top icing do the top heaters work? Are there heaters is it off cycle? Is it terminating too quickly? But be honest 18F superheat sounds high to me also. Obviously dont know room temp but sounds to me like evaporator starving, evaporating temperature too low icing up on part of coil that is refrigerating. But tell us defrost type room temp any way I dont mind being shot down in flames. I know its an old thread but someone may reply.

[mcunliffe4]

If the system is on pumpdown have you checked to see if solonoid passing

[Magoo]

The old "who knows how to set superheats on Tx valves ", problem. Perhaps NH3luva could chime and help, since I annoyed him recently.
magoo

[qqjersey]

Sounds like it is not pumping down, check if overcharged or receiver to small.

[oldesky]

I would suggest you set the superheat to 5.6K or 10°F first and see how the system operates. I would think the evaporator is running at a low evaporating temp causing it to ice up and the high superheat is starving the rest of the coil.

[9 below zero]

Had a simular problem some time ago except icing up at the bottom of the coil,in a beer cellar,Cutting out at 10c.
never did find out why.

[coolhibby1875]

18 degrees supaheat is way to high you are really looking to get between 4 and 8 degrees c supaheat, wouldn't imagine the compressor will last to long with a diff of 18 degreesc

[frosty74]

what make evap coil is it?
some evap coils have an orifice in the distributor which size has to correspond with the gas type have you checked that?

[Royal241]

it could be that when you pushed the orifice thingy inside the distribuitor it fliped, or just not perpendicular, therefore feeding at at different flow, I've seen that in new installs...