I've an R22 walk in cooler that's not keeping temps real well. Target temp is 34°F or 1°C. This cooler has NO history of ever running correctly. The cooler will recover well to it's best temp even when subject to a sudden and heavy heat load, but never does fully come down to temp.

I've verified the thermostat is set and working correctly. Pressures look good for R22 medium temp, sight glass is clear but I'm seeing excessive hunting on the expansion valve, from 1°K to 10°K.

A quick inventory of the cooler shows a 26.6kBtu/h evaporator, a 28.5kBtu/h condensing unit and a 18kBtu/h expansion valve.

I'd have expected an over sized valve to have hunting problems, but this valve appears to be undersized for the application.

First thought had been to simply replace the thermal element, but I'm leaning towards replacing the whole valve.

Have I missed something obvious or does it look like I'm on the correct path?

Thanks!