Arkansas HVACR NewsMagazine January 2025

HVACR NewsMagazine January 2025

Tech News

Testing Defrost We can test the system in defrost to make sure we’re getting the right voltages a heat pump needs to operate as intended. We can jumper out the defrost board to test the defrost cycle itself, but that doesn’t allow us to test the thermostat and whether it opens or closes as it should. Therefore, it’s a good idea to run the unit in heat mode with the fan off to allow a little bit of frost to build up on the coil. Then, the speedup tap makes the board check for defrost at quicker intervals than the timer that’s been set.

Credit: White-Rodgers by Copeland 47D01U 843 Installation Instructions And here is one of Lennox's defrost boards with blinking lights instead of digital displays: Credit: Lennox – Installation Instructions For Replacement Defrost Control Kit (15D57) Used With Various Heat Pumps (pg. 9) Of course, not many of those codes are directly related to the defrost cycle, but they provide a solid starting point for diagnosis. Since the defrost cycle is a function of several controls, we mostly want to make sure that the sensors work properly (i.e., that they either open and close when they should or that they have the right amount of resistance) and that there is voltage in the right places.

The following process is typical of a Carrier defrost board. Each manufacturer will have its own method, and some universal controls have their own testing protocols.