Carrier A/C Compressor making a humming noise

If we've noticed one thing about RV A/C failures:

It's RARELY the Compressor! Most failures stem from:

Dirt,
Controls,
Capacitors,
Refrigerant Leaks

Dirt and Capacitors are easy fixes.

Controls can be tricky, but

Refrigerant Leaks and Compressor Failure usually mean "Replace the A/C Unit" at least for most of us.

Your A/C is 2004, but ten years isn't senior citizen age for the Sealed System (Compressor, Coils and Tubing) in an RV A/C.

We had an OP who worked in A/C on Boats. Thinking of it, Window Units, Boats, and RV's all use A/C of about the same capacity with similar components. In Boats the Condenser is water-cooled vs. outside fan in the others, but Compressor is likely to be similar. He pointed out cases where the Motor portion inside the Compressor Shell had separated from the Compressor portion inside there. In those, you'd hear the Compressor "Running" but no cooling. But that could also happen if the refrigerant had leaked out OR the valve(s) in the Compressor had gone bad.

Do you have access to an AC (alternating current) clamp-on Ammeter like this?
I picked a Harbor Fright item because they're cheap, I could find a photo, and I have one that's been very useful.

Compressor should have a plate or label showing two or three amperages:

"Start" (which many clamp-on's can't report since the compressor shifts into Run so fast)

"LRA" (Locked Rotor Amps) which is when the motor portion can't turn

"Run" which is what a normal compressor, proper refrigerant charge and supply voltage, should draw

You don't have LRA, at least yet. If you ever do, compressor or capacitor bad.

If RUN is Low, Charge could be low, or Valve(s)weak.

If RUN is High, Motor Bearings/Compressor Pistons dragging.

A Compressor Run Capacitor (which all A/C's have) of the wrong value can cause compressor overheat. Hot compressor could have high Run Amps. If you want to get into Capacitors, remove the access cover if you need to, and post a photo of them. Many compressors also use a Start Assist Capacitor and some form of device to cut that compressor out once the unit starts. Photo'd help sort out what you actually have.

OH!!! You may see a Wiring Diagram. Photo that too.

Running the a/c on generator and shore power produces the noise.

I havent checked the voltage yet but will.

Thanks for the feedback.

Read above reply more carefully. Capacitor is only a guess and I don't have much confidence that a failing capacitor would make the compressor noisy. Was Voltage OK? If you're running the A/C at home on a 15- or 20-Amp circuit and/or standard duty extension cord, you could easily have low voltage to the compressor. Still, we've had low voltage and the compressor didn't get loud. Just tripped the breaker.

Yes it is cooling and airflow is normal. I can only hear the noise from the outside. It slightly annoying and I don't wish to disturb any neighbor while at a campground

The noise starts when the compressor kicks in. No noise when it is fan only.

The noise is coming from where the small container connects to the larger compressor tank.

To eliminate bad damper feet, I shook the tank to make sure the noise wasn't coming from the base.

I used a hose up to my ear to locate the source of the noise.

I have no experience with capacitors or the like. I'm pretty handy but prefer not to mess with electricity, if I can help it.

I take it you tried the Fan Only settings and no humming sound then?

It IS cooling, right? Air flow seems normal?

You can run the compressor BRIEFLY with fan disconnected and confirm the noise. Are you sure the outdoor fan blade and inside blower wheel are tight and undamaged?

We had a Coleman that made noise because one of the shock mounts at the base of the compressor got out of place.

Noise also possible if refrigerant lines get to rubbing, against each other or against the cabinetry.

I don't know if a failing capacitor can get the compressor out of phase enough to make noise but capacitors are cheap.

Have you worked on 120VAC equipment? And with Capacitors? If you haven't you'll need some coaching and a Helper/Safety Observer.

Two suggestions:

1. Update this thread with Model Number of the A/C. Maybe we can find a wiring diagram to show how to temporarily disconnect the Fan, and how the Capacitors are connected.

2. Click "Notify Moderator" and ask to move the thread to Tech Issues. This A/C is used by all RV types, and more techy OP's hang out there.

Have you checked the 120VAC VOLTAGE. Being too low will cause that...

It's the compressor

What is humming the fan or compressor?