I have a Lennox Heat Pump Roof Top Unit giving me problems. Model#CHP20-653-1Y Serial#5696L02192. I is tripping out my high head pressure switch on high discharge pressure. The head pressure switch is set to trip out at 410PSI. This seems to be happening in the heat mode when my reversing valve not energized. This switch is located on the discharge side of the refrigeration circuit before the reversing valve. I have monitored the discharge pressure on the unit up to an hour and a half and it hold steady at 280PSI and will climb up to 320PSI when I bring in my auxilary/emergency heat but, that is it, no more than that. This unit is tied in to a energy recovery unit using 100% outside air. I have checked the filters and the belts and everything is fine. Direct Driven Blower motor in the Lennox unit works of some ice cube relay's. The only way I can get the high head pressure switch to trip is when I disconnect my blower motor. Any suggestions? It seems to happen when I am not at the site in the heating mode.