My AC Guy Says My Compressor Is Grounded

Your AC guy says:

“Your compressor is grounded.”

If he actually tested it and confirmed that?

Yeah. That’s bad.

Unlike some diagnoses where we need five different measurements and a long conversation, a compressor winding electrically shorted to ground is a legitimate compressor failure.

What Does “Grounded” Mean?

Inside your compressor is an electric motor with windings.

Those windings are supposed to be electrically isolated from the compressor shell and ground.

When we say a compressor is grounded, we’re saying electricity has a path from one of those windings to ground where it shouldn’t.

That’s not:

“Your compressor is getting weak.”

That’s an electrical failure.

How Do We Test It?

With power safely disconnected and the compressor electrically isolated as needed, a technician can test between the compressor terminals and ground.

We’re looking for electrical continuity or measurable resistance where there shouldn’t be any.

A proper insulation-resistance tester, commonly called a megohmmeter or megger, can provide an even better evaluation of winding insulation condition.

If a compressor terminal has a confirmed path to ground?

Your AC guy isn’t making that up.

The compressor has a serious electrical problem.

Could Something Else Make It Look Grounded?

This is why proper testing matters.

We don’t want to test through connected wiring and controls, get a strange reading and immediately condemn a compressor.

The compressor should be properly isolated so we’re actually testing the compressor.

And there’s another wrinkle:

A compressor that has experienced a severe electrical failure can contaminate the refrigeration system, so replacement isn’t necessarily as simple as:

Take old compressor out. Put new compressor in.

The refrigeration circuit may need additional cleanup and precautions depending on the failure.

Can a Grounded Compressor Be Repaired?

Not internally in the field.

A residential hermetic compressor is sealed.

We’re not opening it up and rewinding the motor in your driveway.

The practical repair is typically:

replace the compressor

or

replace the system.

Which one makes sense depends on age, warranty, refrigerant, equipment condition and repair cost.

What Should You Ask?

Ask:

“Can you show me the reading to ground?”

If your technician isolated the compressor and can demonstrate that one or more terminals are electrically connected to ground?

That’s pretty compelling evidence.

The Klein Answer

If your AC guy says your compressor is grounded and he actually proved it electrically:

He’s probably right.

This isn’t one where we’re going to tell you:

“Maybe it just needs a capacitor.”

A capacitor can prevent a compressor from starting.

It doesn’t repair compressor windings that have shorted to ground.

Now the conversation becomes:

Compressor replacement or system replacement?

That’s where age, warranty and economics come in.

But as far as the diagnosis goes?

Sometimes your AC guy puts the meter on it and the answer really is:

Yep. Compressor’s dead.