Results 1 to 9 of 9
  1. #1
    Join Date
    Jan 2001
    Posts
    66

    delayed start for ac

    My second floor air conditioner (Trane 2 ton about 10 years old) frequently does not start up until 5 or so minutes after I set the thermostat to cool.
    Once going it is fine, and cycles properly, so when the weather is not too hot, rather than turn the ac switch to off, I set the temp to, say, 85 degrees, and then when the weather gets hot again I reset it to 78 and it comes on right away.
    When the problem occurs the thermostat icon blinks suggesting to me that it is sending a message to the ac unit, but I either have to wait 5+ minutes or sometimes turn the thermostat off and then on a minute or so later.
    What seems to be the problem?

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,389
    Triggering a time delay in the thermostat.

  3. #3
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Many thermostats have a 5 minute start delay to protect the compressor. Usually it's only from the previous cycle or after power is lost.

    As a side note, it's more efficient to just leave your unit set to temperature you want in the morning and leave it there and only set it 1-2F lower after 9PM when you go to bed. AC system are the least efficient when it's hottest outside at 3-8PM. SO the energy you save by not running it all afternoon is lost trying to remove all the heat and humidity during the hottest part of the day, rather than just cycling periodically all day long.

    Besides, if properly sized in hot weather, it should take 3-4 hours to recover 3-5F.

  4. #4
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,512
    Sounds like normal operation of a digital thermostat

  5. #5
    Join Date
    Aug 2008
    Location
    Booneville, Mississippi, United States
    Posts
    255
    Does the tstat have batteries? Weak batteries can make a stat run funny.

  6. #6
    Join Date
    Jan 2001
    Posts
    66
    Batteries are ok in the thermostat, and I do have the thermo programmed to go on in the morning and off at night. But, for examples, the first time I turned on the ac for this season it took a long time to kick in, and recently when we have had severe thunderstorms I decided to turn off the ac thinking that a lightning strike would be less likely to damage an ac that was not running. When I turned it back on, took 5+ minutes to turn on. I also have a Trane for the first floor and have never had this problem.
    Since this is a fairly recently phenomenon (last two years) I am assuming that there is some problem with either the thermo or ac. I can live with this as long as I can feel that this is only a minor quirk.

  7. #7
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,317
    You've got a 5 minute lock out timer in thermostat, or the outside AC unit. Either way I'd not worry about it.

    P.S. Have your children and all the grandchildren move in with you and you'll not even notice when the AC starts and stops!!! Lots of folks are calling us because they "notice" something about their AC as they worry about it when weather is this hot!!

  8. #8
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,946

  9. #9
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    3,948
    Quote Originally Posted by motoguy128 View Post
    Many thermostats have a 5 minute start delay to protect the compressor. Usually it's only from the previous cycle or after power is lost.

    As a side note, it's more efficient to just leave your unit set to temperature you want in the morning and leave it there and only set it 1-2F lower after 9PM when you go to bed. AC system are the least efficient when it's hottest outside at 3-8PM. SO the energy you save by not running it all afternoon is lost trying to remove all the heat and humidity during the hottest part of the day, rather than just cycling periodically all day long.

    Besides, if properly sized in hot weather, it should take 3-4 hours to recover 3-5F.
    IMHO it's better to let the unit run one long time to recover in order to reduce cycling losses. A/C units have to run 10 minutes before pressures stabilize and the unit can operate at maximum efficiency. When cycling on/off all day it won't hit the 10 minute run time unless it's really hot. This can be compounded by electricity prices that vary during the time of day, which vary from utility to utility.

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