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Thread: Cycle Times

  1. #1
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    Cycle Times

    Hey Gang,

    I know this has been brought up in another thread or two but I wanted to consolidate some conversations and ask a question.

    I believe somebody stated a 10 min on/ 5 min off cool cycle was considered good. My question is, under what parameters is that taking into account? I mean, 10/5 on a 95 degree day? Or 10/5 when its 74 outside and set 74 inside?

    I guess I'm trying to figure out if my system is short cycling or not. It does not stay on for 10 minutes (even though my Honeywell stat is set for 3 CPH), but it was not more then 80 degrees outside by the time I got home yesterday evening.

    ????

    Jopopsy

  2. #2
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    10 on 5 off, is a 4 CPH setting.

    10 on 10 off would be a 3 CPH setting. And that would be on a warmer day.

    74 in and 74 out. Most systems will not cycle 3 times an hour. Might have a 5 or 10 minute on, with a 20, 30 minute or longer off time.
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  3. #3
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    Quote Originally Posted by beenthere View Post
    10 on 5 off, is a 4 CPH setting.

    10 on 10 off would be a 3 CPH setting. And that would be on a warmer day.

    74 in and 74 out. Most systems will not cycle 3 times an hour. Might have a 5 or 10 minute on, with a 20, 30 minute or longer off time.
    So how does the CPH relate to the actual temperature in the house? If its 100 degrees outside but the stat is set to 3 CPH, does it wait 10 minutes before calling for more cold, even if the room warms up a full degree or two?

    Just trying to understand. I find I call my repair guys less frequently when I understand the things I'm calling about.

  4. #4
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    If it's a hot day where the A/C is going to run constantly to maintain temp, the CPH setting doesn't play a big role in the cycle time. The CPH setting is typically for warm/mild days where the indoor temp is just being maintained, not on real hot days where the A/C needs to run constantly. At least that's what I've noticed with my VisionPRO TH8320.

  5. #5
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    As it gets closer to design temp. it will end up only doing 2 CPH, and then if it gets a little hotter outside yet, it will go into constant run.

    The CPH is not an absolute value. The stat will attempt do provide its set CPH value.
    But as teh OD temps get to the low and high end of design. It will adjust as it needs to, to maintain set temp.
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  6. #6
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    Okay, so then what is the general consensus for setting CPH for a 13 seer system? The stat was set to 3, but I thought it was cycling too fast (maybe I'm just crazy). I set it to 2, but haven't tried it out yet.

  7. #7
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    Vast majority of the time 3 CPH. Gives the best comfort and operating efficiency mix.
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  8. #8
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    Hrm. I'll have to see how this works out. Would it be safe to say that if you system is border line over-sized, setting the CPH to 2 would help short cycling on borderline days? I have a Honeywell VisionPRO - too bad I can't set the degree tolerance on it.

    In case I forget, thanks all for helping me understand CPH.

  9. #9
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    I saw beenthere say in another thread that you can set the thermostat to have more aggressive temperature control, so it might overshoot the temperature setpoint a bit but make the off times longer. It might be worth trying, along with 3 CPH.

  10. #10
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    Quote Originally Posted by RyanHughes View Post
    I saw beenthere say in another thread that you can set the thermostat to have a more aggressive cooling cycle, so it might overshoot the temperature setpoint a bit but make the off times longer. It might be worth trying, along with 3 CPH. Are you sure you can't set a degree tolerance? I haven't looked at the manual in a while, so you might be right.
    Not that I can see. If there is a way to make it overshoot, pls. somebody tell me. I personally think my stat is too picky for my taste. I'd rather it let the temp drift a full degree then kick on rather then it monkeying around w/ .10s of a degree.

  11. #11
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    Its in the install manual.
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  12. #12
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    Quote Originally Posted by beenthere View Post
    Its in the install manual.
    I thought I went through all the installer settings. Is it called something that a layman would not think obvious? The only thing I saw was CPH, and I also set the blower to run for 90 seconds after the compressor shuts off.

    I have festered over this manual for days ... pls. believe me I tell you its not me being lazy. I read EVERYTHING when I buy something.

    On another note, Beenthere you are fantastic. If you are anywhere around PA I would love to have you install something for me when the need arises.

  13. #13
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    I'm in Lancaster PA.

    What model number is your stat.
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