ZRF05 – FUSE

Replacement fuse for HVAC control circuits. Fuses protect the low-voltage transformer and control board by opening on an overcurrent, typically caused by a shorted thermostat wire or a failed control. The amperage and voltage rating for this part number are not published, so match the rating printed on the fuse you are replacing – fitting a higher-rated fuse removes the protection.

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

Specs

• TypeControl circuit fuse
• ApplicationHVAC low-voltage control circuit
• FunctionOpens on overcurrent to protect the transformer and control board
• Amperage / voltage ratingNot published - match the marking on the original fuse
• Data SourceOTP stock record - not manufacturer-verified

Cross-reference numbers

This part replaces the following OEM and aftermarket numbers:

• BRK5
• 313005

Not sure if your number matches? Call (214) 340-9421 or bring the old part in — bench-testing is free.

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.