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Old 08-31-2012, 12:37 PM   #1
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AC cycles on/off (too?) frequently


Hi all,

I had a new HVAC system installed. These days we regularly experience 100-degree temperatures. The AC seems to kick on every few minutes.

Is there (should there be) a hysteresis adjustment in my programmable thermostat?

Should I set it for a two (or 3 or 4) degree window?

Thanks for your suggestions,
Daneel

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Old 08-31-2012, 01:57 PM   #2
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AC cycles on/off (too?) frequently


doesn't sound like it's the TT. I suspect some other limit control but I am not an AC Tech so, not sure what it might be. Maybe a low temperature lockout to prevent coil freezing or something like that OR shutting down due to system coolant pressure control? Might be best to get a certified techie in there.

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Old 08-31-2012, 04:35 PM   #3
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AC cycles on/off (too?) frequently


Which thermostat do you have?
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Old 08-31-2012, 05:31 PM   #4
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AC cycles on/off (too?) frequently


hello . the a/c unit shouldnt cycle on/off that fequently it shud pull it down in temp then cycle off need more info ,,,
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Old 08-31-2012, 06:24 PM   #5
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AC cycles on/off (too?) frequently


put ur gauges on it will show you the problem
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Old 09-01-2012, 12:33 PM   #6
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AC cycles on/off (too?) frequently


Hello again,

Finally found the manual, inside of another HVAC manual. It is a Lennox ComfortSense Model L7742U 7-day programmable thermostat.

Page 24 begins a discussion of "Stage Delay and DIfferential Settings". It looks like Stage 1 (not sure there is a Stage 2) has a default differential of -0.5 to +0.5 deg, but could be set for a larger range.

This is in a category called "Installer Settings". I figure if I am careful not to change anything, I can at least scroll through various settings, take notes and learn more about what I have and how it is set up. Any warnings to the contrary???

Thank you,
Daneel
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Old 09-01-2012, 12:42 PM   #7
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AC cycles on/off (too?) frequently


takes longer than 3 mins to change room temp even only 1/2 degree so, I don't think widening the diff will change the situation..doesn't cost anything to try though...I don't think you can screw up the settings too much..if you do ..just remove TT and battery ..then re install ..should go to default factory settings..there may even be an APP for that on the TT..Good Luck!
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Old 09-01-2012, 12:56 PM   #8
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AC cycles on/off (too?) frequently


Have you tried calling the installers back again.. before you go changing setting I would call them and explain whats going on... for warranty reasons
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Old 09-01-2012, 02:55 PM   #9
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AC cycles on/off (too?) frequently


is the stat over the tru unit return and no getting direct discharge air on it? might want to widen that range too close..short cycling the condenser
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Old 09-01-2012, 05:49 PM   #10
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AC cycles on/off (too?) frequently


That's the correct setting to change if you want a wider swing.
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Old 09-01-2012, 08:40 PM   #11
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AC cycles on/off (too?) frequently


At 17:12 I turned on the AC and set it to cool to 79 deg.

Local Cycle Cycle
Time Start Temp Duration
17:12 ON 85 30 min
17:42 OFF 80 3 min
17:45 ON 80 9 min
17:54 OFF 80 4 min
17:58 ON 80 6 min
18:04 OFF 80 4 min
18:08 ON 80 6 min
18:14 OFF 80 6 min
18:20 ON 80 4 min
18:24 OFF 80 8 min
18:32 ON 80 4 min
18:36 OFF 80 6 min
18:42 ON 80

I am going to keep logging for a while, then record Thermostat settings and fiddle a little.

This just seems like too many cycles for the condenser. I don't really know this. I am guessing that cycling it on-and-off is more wear and tear than leaving it on longer with fewer cycles -- like a light bulb. Is this right?

I have a call into the field engineer who last serviced the HVAC system.

Thanks,
Daneel
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Old 09-01-2012, 08:46 PM   #12
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AC cycles on/off (too?) frequently


The thermostat is in a short, wide downstairs hallway, off a direct return path from the second floor to the return air register.
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Old 09-01-2012, 09:36 PM   #13
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AC cycles on/off (too?) frequently


Set for a larger swing. Sounds like your A/C is a bit over sized.
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Old 09-01-2012, 10:13 PM   #14
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AC cycles on/off (too?) frequently


review TT manual..there should be a differential setting for ON OFF i.e. looks like existing diff is only 1/2 degree...Increase it to 2 degrees...should stop at 80 and NOT come back on until 82..or variation thereof.. if yoy manage to reset differential and find 82 too warm then just set stat at 77 it should then cycle between 79 and 77 and should run longer between cycles..note that it ran 30 mins to go from 85 to 80 therefore 2 degree diff should run about half that time..12 - 15 mins...I would think that is an improvement but still a little short...maybe the fan speed should be lowered a little
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Old 09-02-2012, 09:12 AM   #15
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AC cycles on/off (too?) frequently


Keep scrolling through the options until you come to compressor protect. Turning that on will give you 5 minutes minimum between cycles.

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