troubled freezer

[in house worker]

I work at a school as maintence man. I got my refgerent cert. about 2 years ago. I've had 3 freezer problems in that time. About 4 years ago a company evacuted a freezer that had 502 ref and replaced it with AZ-50. the last few days its been running about7-10 degree F. I've cleaned the coil today with coil cleaner and water. It made no difference. My pressures and line temps are 320psi and 115 degrees F on the discharge and 28 psi and 66 degrees F on the suction side. The out doors temp was 81 degrees F. The condensing unit is in a vented storge room with the room temp of 95 degrees F. I added a shot of freon to it which did not help. the temp in the freezer is standing at 10 degrees. Is pressure and the hi side is to high? Is that why the freezer temp is warmer than it should be?
I know the defrost works an the evaperator coil is not iced up. I'm out of ideas.

[Dad]

Can you give a little more info

Suction temp you gave, where did you take that temp?

What is your temperature drop across the evap coil?

How big is the box and how old?

Do you have a good closing door with seal?

Do you have ice droplets on the ceiling of the freezer and on the product?

[basser]

You state 115° on the discharge, are you sure this is correct? If this is discharge temp. it is awful low. Assuming the 28psi and 66° is at the compressor suction your compressor superheat 73° and is high. Do what ever it takes but check pressure and temperatures out at the evaporator. I would suspect a high superheat here also indicating the evaporator coil is starving.

Another thing that would effect evaporator TD would be and oil logged coil. What is the concentration of mineral oil vs. POE lubricant in the system since it was converted? The 507 refrigerant will have a hard time moving the old mineral oil out of the evaporator coil. This situation would effect the temperatures, but probably lower evap. superheat, not raise it.

[melxiv]

is your condenser fan running??? seems your lo and high side are bit high.