3AFUSE – FUSE

A standard 3 Amp bladed ATC fuse commonly found on HVAC control boards protecting the 24V thermostat circuit. If your thermostat goes blank or your furnace/AC stops responding to the thermostat, a blown fuse on the control board is one of the first things to check. Keep a few spares on hand.

Specs: 3 Amp, bladed ATC style, for low-voltage HVAC circuits

Replaces: 00022, 0210003MX, 21603, 24302, 3090003, 3A, 3AATC, BPATC-3

Fits: HVAC control boards, furnace boards, and low-voltage circuits using standard ATC blade fuses

In stock at Open To Public HVAC Parts in Dallas. We test parts at the counter before you buy. Call or text (214) 340-9421.

Specs

• TypeBlade-style control-circuit fuse
• OEM CompatibilityUniversal

Cross-reference numbers

This part replaces the following OEM and aftermarket numbers:

• 3AFUSE

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

Fits these models

• Standard 24V control-circuit blade fuse — replaces inline fuses on furnace and air handler control boards
• Match the amp rating exactly (3A, 5A, or as specified by your unit)
• Common applications: all residential furnace + air handler control boards with inline fuse protection

My 3A or 5A fuse keeps blowing — what's wrong?

Something in your 24V control circuit is shorted or pulling too much current. Common causes: shorted thermostat wiring (animal chew, nick in insulation), stuck contactor pulling locked-rotor amps through the coil, failing transformer, or a shorted gas valve coil. Don't go up in amps — fix the root cause.

Can I use a higher amp rating?

No. The fuse is sized for your transformer and wiring. Going from 3A to 5A will let damaging current flow long enough to melt low-voltage wires or burn out the transformer. Match the original amp rating.

Where does this fuse go?

Typically on the control board between the 24V transformer secondary and the rest of the low-voltage circuit. Some equipment uses inline fuse holders. Check your unit's wiring diagram.

How do I test a blade fuse?

Pull it, check resistance with a multimeter. Near 0 ohms = good. OL / infinite = blown. Visual inspection through the clear housing usually tells you immediately.