delayed start for ac

[Hillside]

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?

[BaldLoonie]

Triggering a time delay in the thermostat.

[motoguy128]

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.

[catmanacman]

Sounds like normal operation of a digital thermostat

[caincompany]

Does the tstat have batteries? Weak batteries can make a stat run funny.

[Hillside]

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.

[wahoo]

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!!

[jpsmith1cm]

caincompany

Please check your PMs.

[54regcab]

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.