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Why did whole-house ac stop working, still blowing but not cold?

The air conditioning worked fine then suddenly yesterday it stopped being cold, but fan still works.

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@jlozier when you say the fan works you are talking about the outside unit? Can you hear your compressor kick in? When you touch the lines coming out of the cormpressor, are they cold/cool/hot? What make and model is your AC?

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If this is a home refrigerated air unit, go outside and look at the pipes going into the exchange unit and see if they are frosted over or even have ice on them. Is that fan running?

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Here is more information, thanks for comments.

While copying the numbers, the unit attempted to start, twice, but went off in a second or two.

I think this indicates that the thermostat is calling for AC but the compressor can/t doesn't deliver.

Is a freon recharge in order? This is something I've never done, but there are access caps on the pipes that go into the house.

The unit is Lennox M/N H529-024-5P, S/N 5805J11611.

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@jlozier you said " the unit attempted to start, twice, but went off in a second or two." Does it no longer come on? Does the main fan turn? Right now it does not sound like Freon issues at all. Sounds more like the start capacitors etc. You got a multimeter? BTW those things pack a punch, so you want to be careful around the electrical connectors etc. check your model number once more. Is it possible that yours is a Hs29-024 instead of H529? Post some images of your wiring and the capacitors (large round cannisters:-) with your question. There are multiple ways this may have been wired up. Don't touch anything and consider turning the breaker off. Remember that capacitors hold a charge long after you turn the power off, so do not touch anything,yet. Use this guide Adding images to an existing question for that.

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You need to take a amp draw to see if the compressor is trying to start. It might be drawing locked rotor and kicking off on the thermal overload.

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@jlozier since this sounds more like a power issue, I would suggest that you check the power to your AC unit first. It should be 240V (depending where in the world you are:-) If you have power to the AC then you want to check the run capacitor. It is in charge of the fan motor and the compressor. Check it for bulging, leaking and/or severe corrosion. If so replace it. The next part on my checklist is the contactor. That is basically a 24V relay that closes the circuit when your thermostat calls for cooling. There are a few different ones for your AC model, which makes it somewhat important that you post some pictures with your question. Use this guide for that since it will allow us to see what you see. Please remember that the voltage and amperage on your AC packs a heavy punch. Do not touch any live wires etc.

BTW you and I will not beable to purchase any refrigerant since that requires a HVAC license and some nifty gauges to refill the unit.

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Thanks, oldturkey and others, this is beyond me, I'm going to call a professional.

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Old question, I know. But I don't see the correct answer here, and I'm seeing wrong information given. It was working fine and suddenly stopped. But the inside unit still runs. And you heard it try to start a couple times. The most likely culprit is the split capacitor outside. What you'll have to do to test this is first turn the power to the outside unit off. There should be a disconnect. Then take the cover off the electrical compartment on the unit. Use a screwdriver to short out the prongs on the capacitor. It shouldn't do anything but I've been hit before by a cap that didn't discharge properly. Then take the wires of the terminals of the cap. Take a good pic before you do so you know where they go. There will be 3 things coming out the top with terminals on it for spade connectors. One will be labeled C for common. Another labeled F for fan. And one labeled HERM for hermetic. This is for the compressor. Use a multimeter that is capable of checking capacitors and check from C to HERM and from C to F. When reading the label on the cap it will tell you something like 35/5 or 45/7.5 or something along those lines. The larger number is for C to HERM. If not within 3% (or 5% depending on what the cap label says) then it is a bad capacitor. The only other thing that can cause it to try and start, but not run, is if the compressor seized internally. But since it sounds like both the fan AND the compressor aren't running, but are trying, then the capacitor is the most likely culprit.

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Mine does that, occasionally, after a power outage and needs to be reset. There are instructions to do that but I hate electricity so my neighbor had me turn it off at the thermostat, then he unplugged it (at the outside power coupling), we talked a few minutes, then he plugged it back in and I turned it back on and all was well.

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John Lozier will be eternally grateful.
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