ILFH – INLINE FUSE HOLDER

Inline fuse holder for low-voltage HVAC control circuits. It splices into the 24 V control wiring and holds a replaceable cartridge fuse, so a short in the thermostat or control circuit blows the fuse instead of damaging the transformer or control board. Fuse rating is not published for this part – fit the amperage the equipment manufacturer specifies for the control circuit.

Specifications from our own stock records. The manufacturer does not publish a public page for this item.

Specs

• TypeInline fuse holder
• Application24 V HVAC control circuit
• FunctionHolds a replaceable cartridge fuse in the low-voltage circuit
• ProtectsTransformer and control board against control-circuit shorts
• Fuse ratingNot published - fit the rating the equipment manufacturer specifies
• Data SourceOTP stock record - not manufacturer-verified

What kind of fuse is on my control board?

On most furnaces and air handlers it is a 3 amp or 5 amp automotive blade fuse protecting the 24 volt side. Match the printed amp rating exactly. That fuse is sized to the transformer, not to how badly you want the equipment to run.

It blew again as soon as I replaced it. What am I looking for?

A short on the low voltage side. Usual suspects are thermostat wire pinched under a panel or stapled through, thermostat wire rubbed bare where it enters the condenser, a bare conductor in the disconnect, a wet or corroded splice at a float switch, and a shorted contactor coil. Shut off the breaker and the disconnect, then disconnect the thermostat wire at the board and at the outdoor unit and add loads back one at a time.

My rollout switch or thermal fuse link opened. Can I just replace it?

Replace it, yes, but not before you learn why it opened. A one-shot link is a record that something got hot enough to need it - a plugged burner or heat exchanger, a blocked flue or vent, a cracked heat exchanger, a dead inducer, or a blower that never came on. Rollout means flame was outside the burner box. Put a new link in without fixing the cause and you will be back for another one.

Can I go up one size or twist in a piece of wire?

No. A fuse is a designed weak point. Oversize it and the next fault cooks the transformer or the traces on the board instead of costing you a dollar.