R502 Freezer not getting under 0*F

[jxwong]

Walk-in Freezer (0*F or less)

-R502 with TXV (ext eqz)
-Temp never gets below 7*F
-Compressor LRA=65.0 (drawing 9-10 amps)
-CPR on suction line
-Defrost timer (4x a day for 30min), termination switch, fan delay OK
-Evap and Cond coils are clean and all fans running
-Suction prz (after accumulator & before CPR) =
20# > -13*F
-Discharge prz (after receiver) = 270# > 117*F
-Condenser delta T = 20*F
-Evaporator delta T = 2-3*F (air temp approx 7*)
-Subcooling = 7*F
-Suction line temp after evap coil = 21*F
-Quick "feel" test for temp drop across filter/drier = none
-Sightglass is clear

I am leaning towards:
a) Crap in txv screen
b) Bad TXV
c) Other

Thanks in advance
(If u need more info/data let me know)

[ateeq.baig]

hello dear
tell the suction pressure at compressor inlet.

[ateeq.baig]

if your suction pressure drops after some time of unit start or suction pressure drops after reaching 6 or 7F then you need to revacume your unit completely
and charge new refrigerant.
because if the air or other gas will be mix in refrigerant then unit will behave just like that.
and adjust your exp valve at factory setting

[nike123]

Check that TXV is at factory setting (use TXV manufacturer instalation literature)
Check equalization line for temperature change
Check that TXV opens and closes by heating bulb with your hand and checking change in superheat. If that make any change in superheat TXV is functioning but could be that his screen is clogged
If that doesn't help TXV is lost its charge or is mechanically faulty.


Non-condensables will make condensation pressure higher, moisture will block TXV and suction pressure will be way below normal.

But, with refrigerant mixtures, and if you are not sure that no one was there before you, it is always best first to recover and recharge with new refrigerant. When you recover, you could change filter dryer and see if TXV screen is clear.

[mbc]

some information is wrong . you put.
-Temp never gets below 7*F
-Suction line temp after evap coil = 21*F
-Suction prz (after accumulator & before CPR) =
20# > -13*F
may be -Suction line temp after evap coil = - 21*F
close TXV untill delta T of Evap. comes for 6 - 7 F

[nike123]

some information is wrong . you put.
-Temp never gets below 7*F
-Suction line temp after evap coil = 21*F
-Suction prz (after accumulator & before CPR) =
20# > -13*F
may be -Suction line temp after evap coil = - 21*F

What you suggesting is physically impossible!

Suction line temperature cannot be below suction saturation temperature.

He has high superheat and 21°F is possible line temperature as oppose to negative superheat and -21°F line temperature, which you suggesting.

[rbsguzman]

Tell me the following:
Compressor or condensing unit model and make
Evaporator Model and make
TXV Model and make
Room and panel size( heavy usage or regular
Equipment conditions

[Gary]

Add refrigerant until the subcooling is 15F.