air conditioning thermostat failure question

this is the 2nd thermostat to fail in 3 years time its a digital Honeywell ct8775a. I live in Florida and it fails in the summer time while on cooling. the thermostat will register the 80 degree setpoint and turn on but not shut off ( thermostat always read house temp at 80) the house was 74 degrees last night, replaced the thermostat and all seems fine. I don't know why these would fail in the same way, should I go with a normal honey well thermostat? (non digital). thanks in advance jeff
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normal honey well thermostat?

Were both failures or the same model? Maybe a bad design, or both made with components from the same batch. Certainly, I would not BUY another one of those, unless you get it under warranty.
If you must have an electronic one - maybe Consumer Reports has some ratings. Else get a simply mechanical one - they last forever.
RichK
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Then why is it, that I've come across faulty ones? <g>
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That's probably just you.
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Yeah, like I'm the only tech that's finding them... <rolleyes>
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Dig wrote:

FWIW, I've had a digital Honeywell (albeit not that model -- mine is a CT3400) for a lot longer than three years, and it has performed flawlessly.
I notice your model is powered from the 24VAC control voltage. You might try one that is battery powered -- perhaps your area has a lot of lightning-related power transients, and they are causing unreliability. You might also check that your control transformer is actually providing a voltage that is within the specs required by the thermostat.
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Dig wrote:

BTW, according to the manual I found on line, the CT8775A is a "heat only" model, so I assumed you actually have a CT8775C.
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thanks for your help CJT, sorry about the thermostat # it actually is CT8775A,C. I have regular maintenance performed by the Company that installed the unit and he said the LV transformer was ok, and yes living in Florida we have a lot of lightning spikes so may be that did it in. thanks again, jeff

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When I tried to inquire about a lightning rod for my house, everyone on the phone assumed I was in Florida.
Surely with the whole rest of the country also having lightning too, that was an unwarranted assumption.
Actually, I wanted to know if I could convert my metal fireplace and metal chimney into a lightning rod. I thought this might be real easy, but like I say, they all thought I was in Florida, and no one could answer my question, 23 years ago.

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cooling.
shut
last
thermostat?
What's the model number? Are you using the exact same model each time?
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Isn't Florida the lightning capital of the US? If you experience a lot of lightning or power surges in your area the resulting voltage spikes could be damaging your thermostat. I would start by measuring the AC voltage feeding the thermostat because sometimes the control transformer could be defective, improperly installed or have the wrong tap from the primary winding hooked up. Many of the control transformers installed in HVAC units have a 208 or 240 volt primary winding selection and if the wrong wire is connected, the voltage from the secondary winding which is supposed to be 24 volts will be too high or too low. If your thermostat is properly installed, there should be 24 volts AC between the red and blue wires. If you're problem is voltage spikes, you can install a surge arrester on your HVAC unit.
[8~{} Uncle Monster
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On Jul 29, 12:37 am, snipped-for-privacy@gmail.com wrote:

A lot of critical info is missing. Like were all 3 the same model? I don't see how 3 different thermostats from diff manufacturers could all fail in the exact same way (goes on showing 80 and never chgs or turns off) from surges. If they are all the same, or at least similar ones from same company, then it sounds more like a weak point in the design.
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All 3 are the same type from Honeywell, the reason for using the same kind was that it had a plug in application and no need to rewire, but if I have to replace the thermostat every season, I will try a different route. thanks to all for the help jeff
----- Original Message -----
Newsgroups: alt.home.repair Sent: Sunday, July 29, 2007 9:33 AM Subject: Re: air conditioning thermostat failure question

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season,
Change to a different model of Honeywell or Robertshaw.
The first model of the digital round (T8700) had a failure, looks like the second model does too. :-(
I've had good results with the following series of stats...
Honeywell FocusPro 5000 FocusPro 6000 VisionPro 8000
Robertshaw 9400's 9500's 9600's
There are many stats from these categories to meet your needs.
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I got a very nice Honeywell pgmbl tstat in '84. Lasted about 3 years.
The White-Rodgers on my wall now has been in service for 20 years. Threatens to outlast -me-.
I'd count 3-strikes-yore-out for Honeywell. Do some homework, id a mnfgr with a good rep and tstat with your needed features, and buy/install.
Honeywell and I are "No Mo'!" (whenever I can get away with it).
P

"Mit der Dummheit kaempfen Goetter selbst vergebens!" -Friedrich Schiller
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