A 3 degree variance is not uncommon in racks, but the 83 reading on the 3rd shelf is pretty off. It does seem strange that your top rack is not the hottest also. Is the ambient air temperature in your room stable? Is there air flow through the rack that may cause uneven temperatures? From the top to the bottom of some of my racks there is about a 3 to 4 degree difference.
Heat cables are tested and true and if used in the proper application are just as good as heat tape. I assume it is possible that you have a dead spot in your cable, where replacing the cable would be the only solution to regulate your temps again. Heat tape is another route you can take, just personal preference and what works best for your rack at this point.
Reply With Quote