Utica Dunkirk SS00801 Pressure Switch The York S1 025 18452 700 Transformer is The York S1 025 18452 700 Transformer is a heavy duty electrical component engineered for precise voltage regulation in residential and light commercial HVAC systems it features a durable electrode and porcelain insulator designed to withstand high combustion temperatures while protecting signal integrity to the ignition control module this SPST (Single Pole Single Throw) switch ensures the combustion blower is pulling sufficient static pressure before allowing the ignition sequence to proceed verify that the switch closes continuity exactly when the system pressure reaches 0