Heat Pumps and Electric Heating - Help checking defrost board

Hello I have a Lennox heatpump that freezes up quite often. I have some electrical background but I am not sure about the total function of the defrost board. I tried to test the defrost board. what I did first is pulled the temp switch and put it in the freezer in the house to see if it would change states. it did so then I jumped it out on the unit and then jumped out the test points on the defrost board after a several seconds the defrost relay clicked and changed states but only changed states for a fraction of a second but the unit never went into the defrost cycle. I am not sure if as to why it did not go into the defrost. have not done somthing right. thanks for any help you may have time to give.