Strange A/C Problem??

I have an 8 yr old house and A/C system. That is my current problem, since I will be leaving for an extended vacation soon, and am very concerned that the A/C could shut down while we are away form southern Florida.
About a month ago, we came home one day and it was 80 degrees in house, so I knew A/C had a problem. Furnace was running, but compressor was not. Called A/C service and they said to shut off furnace. When tech got there next day, and turned on furnace, compressor went on OK. They checked every thing out and it all seemed to be OK. Since it was all running, there was nothing else to do.
Had A/C service with annual tune-up, and tech said all was OK last Wednesday. Today, just got home, and it was 79 degrees in house. Furnace was on, but compressor was not. I shut down furnace for an hour and turned it on. This time compressor was on. I will call A/C service company to check out system, but I am concerned that they if system still working, there is nothing for them to do.
Anyone have a similar problem with a problem such as this? Any suggestions??
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Les wrote:

Battery operated thermostat with weak batteries
Weak motor relay or starting capacitor on compressor
Failing/overheating compressor
You (or someone you hire) will need to methodically eliminate these and other possibilities.
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Thanks for the reply.
I have thermostat with battery backup, but have not seen any low battery messages. Furthermore I changed batteries each year June 1, so that cannot be the problem.
Regarding the other 2 suggestions to check out, can a tech determine if they are a problem if the compressor is currently working? If not, should I just wait for house to heat up again, see that the air handler is working and compressor is not working, and then wait for a service tech?
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Les wrote:

    Generally if the blower in the furnace comes on when calling for cooling, the thermostat is good. It sounds like your problem is at the condenser unit.
    I think you are going to have to diagnose the problem while it is failing. The first thing I would do is measure the contactor coil to see if it was being activated. If it is, then see if the 220 v A/C is being applied to the condenser unit (Compressor and fan). If you do not feel comfortable with electricity, get someone who does. You can get hurt if you do not know what you are doing.
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I'm curious as to why you bother leaving the A/C on if you are going to be away from home for several days. Seems like a waste of electricity to me.
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snipped-for-privacy@gmail.com wrote:

I don't know where in S. FL they are but I lived there in Plantation(near Ft Lauderdale) for 8 yrs and ants got into my contactor on the compressor and fried it(ac guy said it was common there). The ac was out for two days I left for work in the morning and when I came home that night there was a teepee of tiles that poped running accross the middle of my family room. From the expansion. So it may not be a waste of elec.
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Here in Florida and other humid areas it is a good idea to leave the A/C on. But the setting can be something on the order of 80*, just to keep the humidity down in the home. Otherwise mildew will be a worse problem than the small amount $ spent to keep the A/C running.
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Bishoop wrote:

I live in a humid area (Baltimore) and would be OK leaving my AC off all summer if my house were unoccupied. Having said that, the OP's real problem is that they do not want to leave on an unreliable A/C unit when they are away on vacation. In this situation I'd probably just get a dehumidifier and use it and leave the A/C off. Assuming that they could find a way to get it to drain into a drain, it should be OK.
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Les wrote:

working, but which is known to experience intermittent failures, will just start replacing the likely components. That might work, or it might just be an expensive waste of time.
You might be better off waiting for it to fail, and exercising your own best powers of observation (e.g. is anything buzzing? smelling like it's burning? is there anything unusual on the thermostat's status display? etc.)
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Les writes:

Another possible diagnosis: condenser fan motor has sticky bearings, doesn't start reliably, unit overheats and shuts down.
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Les wrote:

Yes, evacuate the house immediately and call the God Squad. Have them exorcise your house with distilled holy water (no staining).
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