Bad evaporator coil?

[Telecaster1]

I have a question that I think I know the answer to but I would like the advise of fellow members of the trade.

I have a walk in cooler that runs on 12 with a evaporator that is looks pretty beat up on the coil. If I try to straighten the fins out, they just come apart. With a 100 degree ambient I have about 185 on the head with about 11 degrees of subcool. I had a super heat of about 21 degrees at the evaporator and adj the TXV to about 10 so there would be some cool vapor going to the compressor (25' line set that had about 70 degrees at the compressor previously). After the TXV was adjusted, I went and put my probe on the suction at the compressor and noticed a hunting SH between 10 to 30 degrees. Have a delta T at the evap of about 3 degrees, 48 in and 45 out.

This all started when I was setting the thermostat to get the box below 40 degrees. This caused the evap to frost at the top after a couple of days. After I adj the TXV it started to frost even worse. I looks like a lack of heat transfer and I'm attributing it to the beat up evap.
Thanks

[A1 Burt]

what is shouting off compressor temp control or pressure control ?

[jpsmith1cm]

In all of that, I don't believe that you mentioned a suction pressure.

[Telecaster1]

24# final suction press. I have to add the box did get to 35 degree which is where the stat is set. I watched it after the kitchen closed while I was working on an ice machine. It seems the only time the condenser shuts of is when the kitchen closes and the door stays shut. The evaporator started to freeze a couple days later during the busiest hours.

[jpsmith1cm]

24# is more than a bit high for R-12 if memory serves me correctly.

I was always taught that, for med temp, 18# is a fair target, equating to about 15 degrees coil temp.

If you aren't overcharged with 11 degrees SC, look at an inefficient pump.