Hi. I have a central air system. Our air conditioning has been fine for the last few years, but this year, I have a weird problem. After working fine all day and evening, around 10 p.m. every night, the air conditioner compressor does not go on, yet the fan inside the house stays on, essentially thinking that the AC compressor is.

I had a service person out here, and the AC system was working fine when he came (figures). I switched out the capacitor, just in case since there was some rusting, but other than that, the repair folks could see nothing wrong.

After having this occur for the last week, I went out today, bought a new thermostat, successfully installed it.

The same problem occurs. The temperature rises, the fan kicks on, the thermostat shows that the compressor should kick on, but nothing. The fan just keeps blowing.

Again, it works fine completely through the evening. It's specifically at around 10 p.m.

I do have my sprinklers on outside at this time, but for the last two years, that hasn't bothered the AC unit at all... and the sprinklers are also on in the morning and the AC works fine then, so it isn't any issue with water from the sprinklers.

For some reason, the actual compressor won't turn on after a certain period at night. Everything is programmed correctly, and this happens on both the automatic and manual settings.

Anyone have an idea what the deal is? Before I blow another load of cash on having a service guy come out in the middle of the day and finding nothing wrong, I figured I'd start asking folks on here.

Thanks.

Is this a heat pump? Please give more info.

From reading your post, I'm not sure if your talking about the "outside unit" as a whole or it's parts. The outside unit is made up of a compressor and a fan.

You may be saying that the fan outside doesn't come on after 10:00 PM, rather than the compressor stops. The compressor hums and the fan, you can easily determine if it's running.

There is the possibility that your "outside unit" has two fan speeds. The lower fan speed is used when the temperature outside drops.

But first, determine if:
1) The fan on the outside unit isn't working
2) The compressor on the outside unit isn't working
3) Both the fan and the compressor are not working.

You might have to place your ear next to the outside unit to hear something,

Hi,

Thanks for the responses. Let me clarify.

By "fan," I mean the inside blower that intakes the air. That fan continues to work, while, the outside AC unit (the whole unit) does not go on.

This only happens at around 10 p.m. in the evening, after a day of use. It's almost like clockwork.

Right now, at 8 a.m. it's working fine, cooling the house (which the t-stat reads at 77 down to 74 like it should). It'll work fine all day long until about 10 p.m.

The only thing I have noticed is that as the day goes on, the inside blower/fan/intake will come on, and it takes progressively longer before the outside AC unit (compressor/fan) actually kicks on. And then like I said, at about 10 p.m. it stops coming on all together.

This has never happened before in the years I've owned the house, so something IS wrong, I just have no idea (nor did the AC service person, since when they came over, nothing was wrong) what the problem is.

Hey I am having the same problem this week. Please share what was the cause and fix if u have fixed it.