i work on alot of carrier package units, thanks to walgreens. roughly 10 tons 2 stage cooling , 2 seperate circuits. anyways i seen there is a pressure switch on the discharge line and one on the liquid line! its NOT a heat pump, they are all like this so i assumed one on liq. line was a fan cycling switch until i said let me trace the wiring. pressure setting is faded off anyways they are in series together tied to the famous carrier lockout board. Why 2? i called tech support the guy told me the one on the discharge line is hi press. cutout. the one on the liquid line is a loss of charge (similiar to a low press switch). he said they do that on all the heat pumps so in the heat mode it will sense low pressure. ok cool but this is not a heat pump then he told me no even on the straight cool units they still put it there from factory so there is no confusing on the location. he said in this situation it serves no purpose and basically i have no low pressure protection. i think that is really stupid who do they have installing them??????????