What causes a heat pump transformer fuse to blow?

What can cause a heat pump transformer 5a fuse to blow? If it blows during the inspection, would you pay for it?

A direct short most common is a dog chewing the Stat wire between the outside wall and the unit you have both the common and the hot wire going to the outside unit and if they touch you no longer have a fuse. The hot wire is not active until the stat calls for heat or cooling.

If the fuse blew it would be a case of failed during testing and I would not pay;-)

If you so feel obligated, then if I was you, I would pay for the 5 amp fuse yes (but that’s it}. Juan, more than likely it’s two wires / conductors, rubbing together, shorting out, it could even be shorting on the screw heads (5 amp fuses protects the low voltage side).

It could be a number of things: a short, the low or high pressure switch wiring starting to short on the refrigerant piping inside the condenser, the CLO board could short out and kill fuses, and it could be the economizer, if it has one.

5 amp fuses have a tendency to blow out quite often on HVAC units.

Take care and stay safe.

Well said Charley.

Thanks Charley!

Good to know. Thanks Mike

You’re welcome Juan.

At least there is a fuse and you don’t have to replace the transformer.

Where you chewing on the control wire?

More seriously, if it blew when you were at the T-Stat, before you went near the unit / control wire, it obviously wasn’t your fault. If it blew while you were standing at the unit with the cover in your hands and your foot on the wire, you might have something to do with it. I knew an inspector who used to carry the fuses around with him for such an event. I did for a short time but quit because I never had one fail.

That’s a good idea.

I’m not sure when it blew. The HVAC system was working when we tested it, but wasn’t working when the home owner got home. The invoice only says they replaced the fuse. No repairs to the wire were done, so I assumed we didn’t damage anything. I didn’t pay the service call.