A/C Troubleshooting

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zzyzzx wrote:

That's pretty nearly correct -- I generally drive cars with manual transmissions, which rarely fail.

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snipped-for-privacy@gmail.com wrote:

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

Now THAT'S absurd.
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Mike wrote:

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

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.
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Mike wrote:

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
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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?
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Mike wrote:

No danger. AC capacitors do not store charges.
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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.
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hr(bob) snipped-for-privacy@att.net wrote:

Power may be removed but the motor windings are not. Any charge on the capacitor will be drained immediately.
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HeyBub wrote:

Some of the electrolytic start capacitors actually have a resistor soldered across the terminals. You really may only see it on commercial equipment.
TDD
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Mike wrote:

Depends on the size of the hvac tech's boat payment.
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Trip charge, plus an hour's labor, plus the cost of the capacitor.
--
Christopher A. Young
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The Daring Dufas wrote:

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.
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Hipupchuck wrote:

That's because the majority of us Americans are the decedents of Europeans.
<sticks tongue out and blows a bronks cheer>
TDD
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