Ac Staying On

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Old 07-12-18, 11:07 AM
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Ac Staying On

Greetings everyone, new to the forum and new to home ownership. My new house is 1000 Sq ft located in NJ. I'm still not quite moved in yet. I bought the house after it was rehabbed and it was given a new Ducane HVAC system. Its mated to a non-programmable honeywell thermostat. Since the stat is non programmable I've been leaving it set to 77 degrees. I'll get to the house at around 9 or 10 am when it's right around 78 degrees outside this past week. The system will not be running when I get there but once the temperature outside goes up to the low to mid 80's the system will come on and basically not shut off. It seems like it will run for hours at a time with it never going up or down on the set temperature.

My father's house is quite a bit larger just down the road with a much older system and nest thermostat but I've noticed his cycles on and off and will go for extended periods of time with out needing to come on. I've had HVAC professionals check out the system a few months back for a unrelated issue and it is fully charged with coolant.

My questions is should I be concerned about this or is it just the house needing the system to run like this?
 
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Old 07-12-18, 12:32 PM
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Welcome to the forums.

Not quite following you there but the A/C should be running if the room temperature is 1 degree over set temperature.

If I set my house to a certain temp.... the A/C will usually cycle to hold that. If I put the A/C on after the house is heated up..... the A/C will run quite a while to cool the house and then it will start to cycle. If it's really hot outside my A/C will pretty much run continuously to maintain temp.

The cycling of a system is dependent on outside temps, humidity levels and the size of the system.

In other words...... it's best to have the A/C start cooling earlier before the house temperature rises to high.
 
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Old 07-12-18, 12:35 PM
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How long the A/C system runs is a function of a number of things: the size of the house, the number of windows (particularly southern facing), how large the A/C is (how many tons), and the relative humidity. If the system is undersized for the square footage and heat gain, or the humidity is very high, the A/C will run for a long time. In particular, if the humidity is high, a lot of the cooling will go to reducing the humidity. Once the RH drops to ~50%, the temperature should start to go down fairly quickly.
 
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Old 07-12-18, 12:38 PM
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There has definitely been high humidity in the area basically all month. The outside temperatures right now are little more moderate. Its not that the system is taking a while to reach the set temp; my concern is that the system will run while sitting at that temperature for a long time.

I have it set to 77 degrees and the entire time the temperature never moved from there up or down according to the thermostat but it kept running and running the system. I know it eventually shuts off at some point in the day because when I arrive at the house in the morning the system will not be running. But shortly after I get there (around 10-11am) it will run basically non-stop with no changes in interior temperature up or down.

Thanks for the responses guys, any thoughts help...looking for peace of mind here.
 
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Old 07-12-18, 12:52 PM
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It's kind of confusing. My father has the same issue.

The thermostat only shows whole numbers but it is actually responding/operating in tenths of a degree.

From 77.5 down to 76.6 the display show 77. So while the temperature is shown as 77..... it could be as high as 77.5. The A/C will run until the temperature is actually well below 77. Some stats have the ability to set/control cycles per hour. The thermostat uses that and knows how fast your system can recover. It may allow the cooling or heating to operate considerably past the setpoint to hold the cycle per hour algorithm.
 
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