A/C Troubleshooting

This is just a lay-person opinion.

The fan motor is a possibility. A dead contactor (switch like device) is more likely. Does not sound like compressor failure to me.

A service man will know how to jumper the motor and force the contactor to determine the actual cause.

Since that is the least expensive part let's hope that is the one.

Colbyt

Taking some measurements with a volt meter is what should be done to determine what is not working and why.

Most contactors (relays) can be manual activated (removing a cover) and push-in the armature.

The most likely cause is : a defective combo Run Capacitor based on what youve described. You wont be able to buy this part yourself ; it is only available thru the Trade and you need to initiate a Service Call.

Not necessarily so. Replacement parts can be easily (though not rapidly) obtained via mail order OR you can take the part to Grainger's (or similar), say "Gimme one like this" and provide the name of an A/C contractor, OR get your jovial and friendly HVAC technician to sell you one off his truck.

Probably neither one. A seized motor sort-of "hums." The only thing that can "buzz" (like a bee) is the power relay.

You can try this: With all the power off, look at the contacts on the power relay. The contacts may be pitted or burnt, thereby preventing a good connection. If so, more life can sometimes be extracted from the relay by filing the contacts down to a smoother surface. This may buy you some time to get a replacement.

While you're at it, might as well replace the capacitors.

Exactly correct up till the last part, I used to buy nad replace my own caps all the time. I upgraded all my units, so haven't had a break down for a while, My advise is to install two separate capacitors, anyhow. That way you only have to replace the bad one, + the separate ones are easier to find. @ $10- $20 they are worth a try, that's less than 15 minutes worth of service call.

You guys are encouraging a homeowner who hasnt had the technical expertise to repair something he can destroy or hurt himself on. All for the sake of a simple service call (??) . Whether he can get the exact replacement or not, isnt the point. And to tell him to buy two independent run capacitors and expect him to wire them in so they work correctly and safely...is absurd im afraid. OP, call an HVAC serviceman to do the job and realize your limitations ; at the same time, he can check out the freon level, do preventive maintenance routines, and tell you the overall performance of the entire system including the inside Unit with Cooling Coil.

Where can I find the power relay? Is this on the outside unit, or inside on the furnace unit?

To a point I agree with you. I lose sight of the fact that a lot of people lack the basic skills to even attempt such a task. I was perhaps lucky, on my first attempt at AC repair, I peeled the sheet metal on the outside unit and quickly spotted the problem. That emboldened me to go deeper the next time. I do have fairly advanced mechanical and electrical skills though, I have worked as a auto dealer line mechanic, and the electrical I've picked up as I went. Having owned several older homes you just learn it, if you have more desire to learn than money for service calls, I have replaced nearly every component, over the years, on various units, except a compressor, & for that I'd call a pro.

Someone has already mentioned blown capacitors. Whenever severe weather comes through the area, all the HVAC and refrigeration repair techs are running around like ants to replace all the blown Chinese made start and run capacitors. If repair techs could find American made capacitors they would be snapping them up. The problem is that the American manufactured capacitors are usually two to three time the price of the Chinese made capacitors and people shop for low price.

TDD

It was just beginning to storm when the problem started last night. I called around and found a service tech who will come out to diagonose the problem for $50. Having no experience with capacitors (and understanding the dangers of them discharging even when disconnected from a power source) I'm fine with letting a pro take a look at it. Hopefully it's just the capacitor and a relatively inexpensive repair.

Anyone know what I should expect to pay if it's the capacitor?

Exactly.

Not absurd. It's the sensible thing to do.

Now THAT'S absurd.

Outside unit. Remove the removable panel and there it sits. Trace the main power wires - they go to the relay. It works like this: The wires from the thermostat in the house (24v) activate the relay which supplies mains power to the compressor and fan. At up to 30, 40, or more amps, you can see this little relay is switching a LOT of power. It is this raw power that burns the relay's contacts. The contacts, over time, become pitted or deformed just like the contact points in the older type automotive distributor.

Before you touch anything, take several digital pictures so that, if a wire pops off, you'll know where it went.

No danger. AC capacitors do not store charges.

I don't know why they keep using unreliable capacitors on motors when it is totally unnecessary. Motors can be made with start and run windings with centrifugal switches which last much longer than caps and are simple and cheap to replace. Must be the cheapness of Americans.

Depends on the size of the hvac tech's boat payment.

That's because the majority of us Americans are the decedents of Europeans.

TDD

They do store charge, if the power is removed at the non-zero voltage crossing. Please know what you are talking about, as misinformation could kill in this case if the capacitor was charged to the peak of the 240 V supply, about 300 Volts.