A small fan was added to circulate air above the products and more rapidly pull heat out of the top units.
T3 is now comfortably below the upper bound of 6 C, and the other temperatures are only slightly lower. This tells us that air circulation is important to maintaining temperature control of the top units.
The T3 settling time shown above reflects the time required for units to be cooled from 8 C to 4.5 C. This is different from real-world operation, which would see the units loaded into the cart already cooled to the proper temperature. However, in the real world the lid will be opened to load and remove units, possible for a minute or two at a time. Therefore, the next test will examine the effect of opening the lid.