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Thread: New AC Question

  1. #1
    Join Date
    Jul 2004
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    I recently had a two stage AC(Lennox) installed which is paired with a two stage furnace. It is controlled with a Honeywell VisionPro thermostat which has been set-up for two stage cooling. We set back the thermostat for sleeping( 76 to 73) and I have noticed something peculiar. It proceeds to 73 fairly quicly but continues to run for up to two hours and still does not turn off. Is this normal for this type of cooling or is there something wrong with the setup.There is not humidity control on the thermostat. Nighttime temps have been in the low to mid 70's. Thanks.

  2. #2
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    So you set the air conditioner for 76 during the day but 73 during the night??? If it were the other way then I'd suggest that maybe Honeywell's adaptive recovery feature is doing that too you. But as it stands I don't know.

    Whether adaptive recovery has anything to do with it or not, did they leave that feature on or turn it off? Let me guess. They didn't mention it and you have no idea what I'm talking about.

  3. #3
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    Jul 2004
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    Thanks for your reply. Believe it or not, I do know what the adaptive recovery is. It actually works both for increases and decreases in temp. Do you suggest turning it off and see what happens?

  4. #4
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    Well first I still want to know if you're setting the air conditioner lower at night than at day. That would be most unusual.

    What I was getting at with the adaptive is that it runs the system ahead of time to reach the temperature you're requesting by the time it's set for. But (as far as I know) it doesn't keep running the AC after the temperature setting goes up. So if you had it at 73 late evening and then at say 11 PM it's set for 76 then it should just shut off completely for quite some time until it goes into recovery mode in the early morning.

  5. #5
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    Jul 2004
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    Your assumption was correct. We like sleeping in cool temps but do not mind it a little warmer during the day( like winter). The temp drops from 76 to 73 in about a half hour but continues when it reaches 73 for up to two hours. If I then set it to 74 it turns off a and cycles appropriately the remainder of the night. I was thinking that since the thermostat only has a spread of 1 degree, and the AC is likely in the lower stage at that point, that there is not enough cooling to drop it the last half degree or there is something wrong with the thermostat.

  6. #6
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    Those thermostats are full of "Honeywell voodoo". There are settings that tell it to cool more or less aggressively. And they also measure temperature in fractions of a degree, even though they don't display that information. So it could be some simple adjustments to the installer setup of the thermostat that's need.

    Or... I don't know. Be advised that many air conditioners don't cool as well when the outside and inside temperatures are nearly the same. And should the outside be in the sixties then you can potentially get some icing of the evaporator coil. There are a lot of variables involved. So I obviously don't know exactly what's going on. But it's worth a mention.

    It's a new system so I'm sure the installing contractor will have a look if you ask.

  7. #7
    Join Date
    Apr 2005
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    Tampa, Florida
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    Originally posted by sbudnick
    I recently had a two stage AC(Lennox) installed which is paired with a two stage furnace. It is controlled with a Honeywell VisionPro thermostat which has been set-up for two stage cooling. We set back the thermostat for sleeping( 76 to 73) and I have noticed something peculiar. It proceeds to 73 fairly quicly but continues to run for up to two hours and still does not turn off. Is this normal for this type of cooling or is there something wrong with the setup.There is not humidity control on the thermostat. Nighttime temps have been in the low to mid 70's. Thanks.
    Sounds like it's doing exactly what a 2-stage system is designed to do. For kicks, try lowering the set point a degree or two and see if it does the same thing, my guess is that it will. Now, if the temp goes below the set point and keeps running, then you've got a problem.

  8. #8
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    Chalk it up to a lack of sleep. tpa-fl has a very good point. Though two hours? It stills seems like a bit much.

  9. #9
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    Keep in mind we're dealing with a Honeywell thermostat... Rediculous amounts of calculations and predictive algorithms. Depending on how the AC system is sized, in this case I'm assuming it's undersized, that first stage of cooling probably only holds 30-50% of the cooling load, (hopefully more towards the higher end of that) which might just be enough to cool off the place. He's coming down from a 3F setback, so once you get the air cooled, then you have to cool down the objects & building, so it's very plausible for it to take that long when the ACs trying to do this with only one stage activated.

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