My heatpump quit running. I got it running again i don't understand. It has a pressure safety switch circuit that after the 3rd instance that the unit goes off during one demand cycle, the defrost board will lock out the unit. What causes the pressure to open the pressure switch? How can I remedy the problem. I reset the board by breaing the 24v hot lead from the thermost. It is cold out there & momma does not like being cold.