New thermostat on/off cycles 10 minutes


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Old 06-09-10, 03:42 AM
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New thermostat on/off cycles 10 minutes

What a great site! Thank you to all.

A week ago I had a new Honeywell PRO 3000 (non-programmable) thermostat installed to replace a similar Robertshaw 9400. The AC runs and restarts at about 10 minutes intervals. Between 9-12 minute differences depending on time of day. I am retired at home so do not need programmable T-stat. (One more thing to worry about.)

The T-stat has 1 degree differential and cannot be changed. Honeywell says 5 times per hour is normal. This seems excessive to me. The old one ran less frequently. I keep the temp at 81 to save starts/stops. That's comfortable for me. Please note its been 90 outside the past few days.

Should I get one with more differential? I have read frequent on/off is hard on the system plus costs more electricity. Any response is greatly appreciated.
 
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Old 06-09-10, 08:39 AM
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I hope the t-stat is located where cool air from diffusers doesn't directly affect it.

Yes, I'd buy a reasonably priced t-stat that has an adjustable differential spread, 1 degree with a cooling anticipator is not enough spread!

The A/C may also be too large a tonnage, but if it gets the humidity down enough you will be comfortable with a wider temp differential.

That will improve the SEER performance of your system.
It takes over 5-minutes to achieve nominal cooling, so it's just getting going & it shuts down to restart the cycle again.

That is extremely inefficient, & very little condensation takes place to reduce humidity!

Slowing the blower down to 350-CFM per Ton of cooling, or to 700-CFM will slow the sensible cooling rate for longer cycles & increase the condensation of latent heat - humidity - due to a colder coil & longer run cycles.
 

Last edited by HVAC RETIRED; 06-09-10 at 08:51 AM. Reason: Clarity... a colder coil & longer run-time cycles
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Old 06-09-10, 11:41 AM
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Thank you for confirming my thought. I will have an AC man come to check everything (reference from friend). Someone else was here a month ago for annual check-up and, unfortunately, he did not do much for annual check-up but pushed to replace entire heating/cooling unit. Before installing new T-stat there were no problems. Again, great site and thanks for being here for so many.
 
 

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