McDonnell & Miller 63-M-HD Head Mechanism 30067439-890 or use a multimeter to

or use a multimeter to verify the microfarad reading is within the 145-175 range

which can be trimmed to fit specific cabinet depths if necessary

for severe burnouts

or condenser fan failure

it is technically best practice to install it in a position where gravity doesn't compete with the internal spring

McDonnell & Miller 63-M-HD Head Mechanism 30067439-890 or use a multimeter toThe McDonnell & Miller 63 M HD Head Mechanism (Part Number 143200) is a heavy duty replacement head mechanism designed for the Series 63 Low Water Cut Off. Engineered for both hot water and steam boilers, this manual reset mechanical control ensures critical safety by interrupting the electrical circuit to the burner in 15 psi steam or 50 psi water applications. It features a robust float operated design and includes the No. 2 M switch, providing