central AC stops before reaching set temperature?

[blahsome]

I was having trouble with my thermostat, so I replaced it with a Honeywell CT3500 programmable thermostat. Now I manually set the desired temperature to 78, the AC comes on, but stops around 81. My old thermostat will not stop until the room temperature reaches 78....

I noticed that the snowflake symbol (this indicates the thermostat is calling for cooling) disappears at the same time the AC stops. This seems to me the thermostat is telling the AC to stop, no? Why does it do that?

Again, this is in manual mode, without any program in effect.

Is this a thermostat problem, or a problem with AC itself?

 

[huesmann]

How about you set the Tstat to stop at 75 and see where it stops?

 

[shilala]

You have to leave a 4 degree difference between the heat setting and AC setting. Heat 72 AC 76.

 

[blahsome]

How do the AC and heat settings interact? Why should there be a 4-degree difference between the two?

Thanks.

Originally posted by: shilala
You have to leave a 4 degree difference between the heat setting and AC setting. Heat 72 AC 76.

 

[CtK]

on my central A/C control unit it has an option on how many degress b4 it reaches the temperature i set it at
like if its set at 2 it and the temp is set at 70 it will turn off at 72
have no idea why they have this feature but it was wierd so i read the manual and found this option and set it to 0

 

[Saulbadguy]

Did something pop out of it?

 

[blahsome]

My manual doesn't say anything like a temperature spread, but it does have what's called a Smart Response feature, the default of which is On. One would think operating under the manual mode should effectively turn it off. I don't totally understandwhat effect that option has, but I'll try turning it off tonight.

 

[GreenGhost]

Is it easy to change at thermostat? Anything special? Mine is not turning off correctly; last night I had to get up because it was blowing continuously and went down all the way to 69F.

 

[blahsome]

It's pretty easy.

 

[eelw]

Since it's new, I'm assuming it's a digital thermostat and not an analog model with a mercury tube inside. Because it's an analog thermostat, it's not properly leveled then.

 

[shilala]

Originally posted by: blahsome
My manual doesn't say anything like a temperature spread, but it does have what's called a Smart Response feature, the default of which is On. One would think operating under the manual mode should effectively turn it off. I don't totally understandwhat effect that option has, but I'll try turning it off tonight.

The temperature spread is so that you can set the thermometer on automatic and the drift in temp doesn't cause the heat to go on, then the AC to go on, then the heat to go on, etc.
If you set up the numbers wrong it will just default to not running or shutting off to early, or a lot of other goofy things.
To qualify, I haven't worked with many different thermometers for 6 or 7 years, so this may now be a moot point.

 

[blahsome]

My thermostat must be manually switched among heat -> off -> cool. There is no automatic setting per se. So I guess it won't drift anyway...