There is a Compressor and there is a FAN. Now, When the FAN shuts off from the tstat, the compressor should stay ON if the relay is defective. If both the FAN and Compressor shut OFF when the tstat temp is reached, you relay is working. One thing you can do, is swap the front and rear control boards. If the problem follows the control board you have a defective control board. Are you POSITIVE that when operated by the tstat and the system shuts OFF, that the compressor does not come on in the next 10 to 20 minutes by itself? Doug