Carrier A/C Compressor making a humming noise

I will be able to determine which unit is better. It seems the Carrier unit had a stronger fan. I will be able to make a comparision shortly.

Thanks again for the input.

That approach oughta get it! Dometic and Coleman/RVP/AirExcel seem to be the choices these days. There's a Chinese knockoff called Advent that's showing up as OEM on some RV's. Cheaper than the two name brands, no less.

We've had only two RV A/C's, both Coleman Mach. They have cooled well and lasted a long time. Interestingly, one of our resident techs liked Carrier above the others, while they were still in the RV A/C business.

For those watching the capacitor discussion, I was able to find a single 12.5-mfd capacitor that could run the fan. Or if the fan was running OK, plenty of 45+5 caps where only the 45 could be used to run the compressor. All that would take is a jumper between the common terminal of the two.

BUT!!! Capacitor was only an item-of-interest. We never confirmed that it was the actual cause of the noise, and we agreed from the outset that replacing the compressor means replacing the whole unit.

In frustration I replaced the Carrier with a Coleman Mach 15. The switch was pretty easy when you use the Carrier to Coleman conversion kit. The RV shop wanted to charge me 250 dollars to make the switch. I took my time but easily could have made the switch in less than 1 hour.

Needless to say I took pleasure in throwing the Carrier unit from the roof to the ground.

I figure I would make the switch and not be worried about my ac unit going out while I was on a trip with my family.

Thanks again JD for all the information. I did learn a lot from this project.

Here is the photo of the capacitor. This project has turned into a real pain. I don't think I will ever buy anything with Carrier in the name.

As you can see the capacitor is 12/45. I tried to locate one and it's difficult to locate. The manufacturer of the capacitor has a website that is not too appealing.

Thanks JD,

I'm going to take a picture of the spec this evening. I like those prices.

If it turns out to be the capacitor I'm goig to have to send you some nice vino.

It'll get too hot to touch, or at least to hold comfortably for more than a few seconds. What are the specs of the capacitor? There should be two values, probably about 5-mfd for Fan and 40-mfd for Compressor. Plus a Voltage, 370 or 440. Here are a couple on Amazon:

40+5 $8 free shipping

40+5 $14 Prime 2-day shipping

We'd need the actual specs to source the right one... Can you read the label, or did PPL tell you the numbers?

Great info JD.

My compressor does get hot. How hot are the compressor suppose to get? After a short time running mine is almost too hot to touch.

I talked to PPL and the replacement capacitor is 90 and available from a outfit in California.

Thanks JD

I should add, PTC is a Positive Temperature Coefficient Resistor, so really PTCR. With no power applied, it's close to a dead short (low resistance). So in your case, it's if the Compressor Start Capacitor wasn't there and the wires were simply connected to themselves. When power's applied, it heats up fast and goes nearly open (very high resistance). That's why I said awhile ago that the PTC is equivalent to cranking your car for the same number of seconds without knowing if it actually started or when.

I mentioned I hadn't heard of a capacitor causing compressor noise. I wonder if it'd be noisy on its Start winding if it never shifted to its Run winding. Maybe from a failing/failed capacitor or PTC...?

Hopefully somebody who knows more about the electronic/electrical issues will jump in...

How Capacitors help Electric Motors, Phase Shift, PTC to put Capacitor In or Out of Circuit... Above my Pay Grade.

USUALLY... An RV has a Compressor Run Capacitor and a Fan Run Capacitor. Your wiring diagram shows those two in a Combined "can" and that's OK. You can replace with another Combined, or with two Individual capacitors, each of the correct value as printed on the Combined one. You just need a jumper between "HERM" or "COM" on the two. You can even use an Individual to replace one side of a Combined if the other half is still working. I'd only do that as a temporary fix, though.

You don't need an RV store to replace your capacitor, although PPL will probably have it. We have two appliance parts stores near home. Both will sell to DIY. Many will not, citing Safety, Legality, Licensing etc. I believe they're just trying to protect their commercial customers' business. Anyhow, the one that just opened closer to my home sells better capacitors at a lower price. Tech there pointed out that there's a durability spec, defining how many operating hours they're good for.

If all you have is that combined cap with a PTC across it, the compressor RUN capacitor is being taken OUT of circuit till it get hot. Then it allows the RUN cap to support the compressor, Time to getting hot is supposed to be the time it takes for the compressor to start. We had a central A/C in house which was set up that way. PTC failed and compressor wouldn't start. New PTC, and it ran again. I didn't understand the system, did not test or replace the Capacitor, it just worked. Here's a Page which tries to explain that.

Above is odd to me, because a "Hard Start" or "Start Assist" kit consists of an additional capacitor (round, hard plastic, around 100-MFD as I mentioned above) PLUS a PTC or some other device like a Relay or Solid State unit to get the boost capacitor out of circuit. The kits connect right across the two Compressor RUN Capacitor terminals which are "C" and "H" in your diagram, right were the PTC shows now. Two popular brands of those are SUPCO (SPP6e recommended by our RV Tech Chris Bryant for RV rooftop A/C) and 5-2-1 (part CSR U1). SUPCO SPP6 uses a Capacitor and a PTC. SPP6e uses a capacitor too but drops PTC in favor of electronic sensing. 5-2-1 claims to have better electronic sensing.

Anyhow, there are A/C units with NO PTC, NO Hard Start, and they work too. Our present house A/C is like that. And,that's the part above my pay grade. It's not clear to me why...

Nothing
PTC Only
Second Capacitor AND PTC (or a fancier device)...

...ALL help with starting?!?!

It seems many if not most RV A/C units have some form of Start Assist. That makes sense since limited Amps are available and sometimes the Voltage is low. It also seems that some RB builders specify Start Assist when they know the coach will have a generator, such as a Class C. And their Trailers don't get Start Assist, the builder thinking they'll always be plugged into a 30A or 50A pedestal. Forgetting, of course, that many trailer owners want to run their A/C off a portable generator, and need Start Assist worse than anybody else.

Oh, well, cheap shot to replace Capacitor and/or PTC. I just haven't heard of a failure in one of those causing anything but compressor overheating or not starting.