I need to do a test on a panel and the surface temperature has to be at
-30C. When I place a thermocouple on the surface of the panel, get the temperature to -30C and then open the door to do the test, the thermocouple jumps to 0C in less than 2 minutes. The question I have is that in order to meet the requirement and test at -30C, it is correct to place the thermocouple on the Class A panel or should I be putting it on the Class B surface (so that the ambient air temperature does not cause the thermocouple to record a higher reading - it at all this is the case). Any advise/insights?