base 87 adjacent frame unit 93 as shown in fig5 cabling from controller unit 31 is routed through cable protector 95 at base 87 temperature sensing chip 91 is located on board carrier 89 so that when received in housing 83 it is located through sensor opening 99 at base 87 with proper materials sizing chip 91 will be in direct contact with the surface of unit 93 being monitored when base 87 is mounted on frame unit 93 housing 83 should be located at the coldest spot on the exterior of the freezer that spot is usually in the center of the case between the bottom of a door 25 and door or case frame unit 93 see fig6 door and frame heaters 103 are located inside doors and or frames of cases 21 housing 83 is configured at cover 85 and base 87 to thermally isolate sensing chip 91 from the warming effects of ambient air temperature in the vicinity of the chip and transfer thereof by the housing to the chip air space pockets 105 and 107 above and around chip 91 respectively and limited housing contact see fig5 wherein only a single locating post 109 maintains board carrier 89 at it position in housing 83 isolate chip 91 from the housing by thus configuring board.