It is definitely warm refrigerant migrating from the condenser that has the largest impact. The moment compressor is turned off the pressures are 10PSIG low side, 240PSIG high side, then the pressures slowly equalize - reducing high side and increasing low side.
This temperature rise does not spoil the products, but confuses the customer.
I have to see how much it goes up with the products.
Having a solenoid valve at the capillary inlet, wired in parallel with the compressor and the fan, will stop the refrigerant migration. My concern is the impact on the compressor start-up conditions - will the compressor handle the large unbalanced pressures in long term, will the circuit breaker blow?
Miki, you sound like you have a decent knowledge of these issues. However, you are missing the boat. The pressures will equalize, as this is the way it is designed. Also, checking any temperature in the air flow is not a correct way of calculating the box temperature. 0 degrees is perfectly acceptable for food products. Using a liquid line solenoid is worthless, for two reasons. The unit is designed for this means, and the migration is not an issue. The real issue is the fact that there is not any problem with this unit. Please do not try to re-engineer this unit unless you have a much better understanding of theory and design. I mean absolutely no harm or offense, I am just trying to help you not justify the situation.
"Fighting Ignorance since 1973 (Its taking longer than we thought)." The Straight Dope.