They are equipped with electrical contact sets that open or close depending on the mechanical actuation resulting from the increase or decrease of the refrigerant gas pressure on a diaphragm. The coding of the contacts are letters A, B, C and D, where A and C refer to the series association of normally closed switching contacts of the low and high pressure switches respectively.
When under low pressure contact “A” will only have an electrical connection with contact “B” which should indicate low pressure. When the down pressure is between set normal values, contact “A” is connected to contact “C” only if there is no high pressure from the high side of the system, if this occurs contact “A” is connected to contact “D” on pressure switches that have this option should indicate high system pressure.
