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?