C645A-E Honeywell Pressure Switches

The C645 pressure switches are safety devices used in positive-pressure or differential-pressure systems to sense gas or air pressure changes.


  • C645A,B models are for use on natural gas, LP gas, or air.
  • C645B1047 includes a scaleplate stop to meet American Gas Association (AGA) requirements for gas-fired boilers with inputs over 2-1/2 million Btuh.
  • C645C,D models are for use on air only.
  • C645E for use with distillate fuel oil.
  • Spring-loaded diaphragm actuates snap-acting Micro Switch.
  • Switch can be wired to turn on alarm.
  • C645A,C and D models break control circuit on pressure fall.
  • C645B models break control circuit on pressure rise.
  • Lockout and manual reset optional in A and C models.
  • Removable, zinc-plated cover protects scaleplate and adjusting screw.
  • Buna-N fiber-reinforced material for increased control diaphragm strength.
  • Pipe tappings allow selection of positive pressure, differential-pressure, or venting connections.