Woke up this morning with the house at 80 degrees. Thermostat set for 74. AC was running but not cooling.

The schedule bumps it up to 80 during the day while we're at work. After the scheduled bumped it up, I put it back down to 74 just to see if it worked. And lo and behold it cools to 74. What would cause this? Already called a/c company to come out this afternoon.

Was the outside unit running when it was not cooling?

Check to make sure the condensate drain has not clogged and overflowed into the drain pan. If the drain pan fills with water, there should be a switch in the pan that will turn off the coil (cooling), but the fan still runs, to prevent water from overflowing into your house.

One time I accidentally bumped the switch in the attic and had no cooling. Took me a while to figure that out.

drain pan is fine
not sure if unit outside was running, but uncooled air was blowing

hoosier-daddy said:

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drain pan is fine
not sure if unit outside was running, but uncooled air was blowing

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If switch is in the drain line for the main unit, it may kick off without overflowing into the drain pan.
Check the main drain for a backup.

TexAg1987 said:

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hoosier-daddy said:

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drain pan is fine
not sure if unit outside was running, but uncooled air was blowing

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If switch is in the drain line for the main unit, it may kick off without overflowing into the drain pan.
Check the main drain for a backup.

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Nah, the switch is on the side of the pan.

hph6203 said:

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Had something similar happen on my A/C. It was a faulty capacitor that could still turn the outside unit on if you gave it a few tries but would only work about 20% of the time until the capacitor was replaced.

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This.
Put a new capacitor in and see if that fixes it. Capacitors are cheap and easy and maybe you save a couple hundred bucks on a service call.

+1 on capacitor going out. Temperature swings probably have it just barely creating enough juice to kick start the fan. Easy test is watching to see if unit tries go start and fan doesn't get going. Can sometimes use a stick to get things moving (like an old school prop plane).

Hopefully you're right on the capacitor and it's not something more serious. And yes I know they're a huge ripoff. I once couldn't find where to buy a replacement and convinced a a/c guy to let me buy one off of him for $50. Ac company wanted like $300 to replace.
This time I'll bite the bullet and pay for the checkup.

Amazon will next-day deliver you a capacitor for $12. Mine went out earlier this month.

Had this same thing happen to one of my units about 2 months ago.

New capacitor did the trick. Running like a top ever since.

Thank you, I never thought to check amazon bc I needed it that day. I'll be sure to get a spare.

Even if it does turn on, you should notice a struggle getting it to start turning.

When mine was going out, the lights would dim as it was starting up. Eventually it quit running.

Whelp, he didn't find one damn thing wrong.

Amazon saved me today on a capacitor, upstairs outside heat pump fan wasn't running. Pulled the panel off and the capacitor was bulging.

Amazon had a replacement for $18 and if I had over $25 I could get it same day. Now I have a spare!

I had a similar issue that was hard to diagnose, but the contactor was burning up.

The A/C would run for a little while. It would run longer after it had cooled for a long time like you described.

A/C guy couldn't find anything wrong, was about to button it back up and happened to be right at eye level and right angle when the contactor started to glow red on a contact. Watched it for a few more minutes and then it cut off.

A few minutes to replace it and was up and running

hoosier-daddy said:

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Whelp, he didn't find one damn thing wrong.

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Swap both the inside and outside capacitors, unless you know tor sure they have been replaced recently. Heck, even then maybe replace them. Maybe you got a bad one. Too cheap and easy not to try.

Pinochet said:

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Used to work in an apartment complex in college and we replaced a lot of contactors. The ants were attracted to that part and would eventually get a layer of ants so thick that the contactor wouldn't close. Really weird issue.

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I grew up in the water well business. Our crews would religiously put cattle ear tags in breaker boxes/pressure switches/etc. to keep out the ants. There was also a spray they used that they swore lasted for years. It was like a dust in an aerosol can. I cannot for the life of me remember the brand.

This is the answer. Make sure your filters are clean, and that air flow is not otherwise too restricted (closed damper, etc).

Also, if you typically use a dense, high performance filter, you may want to switch to a mesh one, at least temporarily, to see if the other filter was restricting too much air flow and causing the coil to freeze.

If it happens again, go to your outdoor unit and find the insulated metal pipe going from it into the house. Pull back the insulation and see if the line has ice on it. If so, coil is frozen.

Milwaukees Best Light said:

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hoosier-daddy said:

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Whelp, he didn't find one damn thing wrong.

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Swap both the inside and outside capacitors, unless you know tor sure they have been replaced recently. Heck, even then maybe replace them. Maybe you got a bad one. Too cheap and easy not to try.

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Huh?

Sounds like a faulty capacitor to me. Pretty common with this heat.

I can assure you your AC guy hates an intermittent problem more than you do.
First thought is run capacitor on compressor. AC tech should have been able to read the microfarads and if it was 5% off change it.
Second thought is float switch. You say it's in the overflow pan but are you sure there's not a second one on the actual drain line or coil safety outlet?
Third, contactor. We have had several that when the points closed just right nothing happened. China.
Fourth, Honeywell thermostat. We've had many that have failed running only the fan, only the compressor, not shutting off the heater, never coming out of time delay. I hate Honeywell.
Fifth, that tent you've got on your unit shading it is causing too high of head pressure which is causing your compressor to go off on overload but you think the units running because you still see the condenser fan spinning. (I'm being a smarty pants about the tent, but seriously your condenser could need a wash job)

Next time it fails do everyone a favor and go outside and confirm the fan and compressor are running. You can verify for a fact that the compressor is pumping by feeling the insulated copper line and it should be cold but not frozen. If the outdoor fan is running and it's not cold, you've got issues.

hph6203 said:

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Had something similar happen on my A/C. It was a faulty capacitor that could still turn the outside unit on if you gave it a few tries but would only work about 20% of the time until the capacitor was replaced.

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Same. Just happened to me yesterday. $220 and we were back in business. Sounds like I need to buy a few extra capacitors and do it myself next time!

agracer said:

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Milwaukees Best Light said:

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hoosier-daddy said:

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Whelp, he didn't find one damn thing wrong.

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Swap both the inside and outside capacitors, unless you know tor sure they have been replaced recently. Heck, even then maybe replace them. Maybe you got a bad one. Too cheap and easy not to try.

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Huh?

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Blower motor has a capacitor.

usually

My guess is coil freeze-up if not the capacitor.

This should go without saying, but remember to discharge the capacitor after shutting off the power when replacing it or the wife may end up replacing the husband... Pretty simple to do...

Same thing happened to me yesterday, fan would try to start but wouldn't turn or turn really slowly. Kick started it with a stick and it would spin for about 30 seconds. Figured it was the capacitor, ran to Ace Hardware and they had them in stock. Replaced it, but didn't fix the issue. Ohm''d out the wires to the fan and they all added up, so I knew the winding was good. Went ahead and removed the fan anyway, disassembled and noticed one of the bushings and the shaft looked pretty grooved. Filed down the grooves on the shaft and swapped the position of the two bush(put the good bushing where the bad bushing was), put it all back together and lubed it the best I could. Ran for about an hour, cooled the house from 85 down to 74 before it stopped again. Ordered the fan on Amazon for tomorrow delivery.