A/C cycles off before reaching temp, then resumes

[hal1]

Don't know if this is normal. Occasionally the A/C (condenser and fan) will turn off before set temperature is reached, then turn on again after maybe 10-15 minutes. Is it possible that it is intended to do this? Is it possible to that it is this was intentionally to maybe be is set to shut off for a while if it's working too hard. Or is there something else going on? I am getting 55-60 degrees out of the vents, so that part seems to be right

FWIW, it's a new build/unit about 5 years old, but if memory serves, it's always been like this.

 

[Bert_]

Constant run is easier on them than stopping and starting.

Probably some setting in the thermostat.

 

[The Cobbler]

not sure for A/C but I was involved in a commercial building many years ago, heated with hot water. the stats would cycle off when close to temp , then resume. the idea was to allow the heat in the rads to go into the room. it was supposed to make for a more even room temperature . but for forced air A/C, that wouldn't make sense IMO .

 

[65ranchero]

If I understand correctly it may be a type of thermostat that is being used.

 

[hal1]

I think you're all answering my question - that it shouldn't be randomly stopping before reaching the desired temp. I don't think it's a thermostat design/feature, and it doesn't happen all the time, just often enough for me to notice - "hey, my A/C stopped, but it's only 78 when I have it set to 74".

But even if it is broken I'm kind of surprised no one has (as of yet, it's still early) has come back and said "oh, I've seen this before, you're Knudsen Valve Solenoid isn't working right" - or something similar

 

[SALIV8]

Maybe a safety is locking it out like a thermal overload. Have you put gauges on it? Check the comp temp next time its running vs cycling off premature.

 

[hal1]

Maybe a safety is locking it out like a thermal overload. Have you put gauges on it? Check the comp temp next time its running vs cycling off premature.

That's above me. I'd have someone come out for one of those 'tune-ups', but this is my concern, and maybe you guys can give me your thoughts on the subject...

I've been told by a real A/C pro that I trust -(my brother-in-law engineer who designs A/C systems for 25 story buildings) that since it's a closed system, there's no good that can come from opening whatever thingy it is to check the refrigerant and the other stuff these guy do on those inspection/tune-ups. Other than cleaning the condenser and making sure your lines are clean and stuff like that, just leave it alone. Your thoughts on that?

 

[Bert_]

It really sounds like a thermostat issue. It'd be real easy to check with a meter.

When it shuts off but is still above the set point check to see if you have power on terminal Y.

 

[SALIV8]

Along with what Bert said, You could also just pull off the outdoor unit access panel and see if the contactor for the Comp is pulled in when the Comp is not running. If it’s pulled in then a safety is locking it out.

Forget about the gauges.

 

[JRC3]

Always start here.

 

[JackDiddly]

If the charge is off in the system it could be going off from a low or high pressure switch in the outdoor unit and then resuming after it shuts down and the pressure starts to equalize. Its possible the charge was never correct if its been a constant since it was installed.

 

[Bert_]

Along with what Bert said, You could also just pull off the outdoor unit access panel and see if the contactor for the Comp is pulled in when the Comp is not running. If it’s pulled in then a safety is locking it out.

Forget about the gauges.

A safety would be wired to drop out the contactor. It would not switch compressor power directly.

The simple answer is check power on the Y terminal. If the thermostat is calling for cool then there should be power on Y.

 

[LS6 Tommy]

Post your T-stat info. Might be as simple as not being level (mercury switch) or the system or anticipator settings are wrong (electronic).

Tommy

 

[TRWham]

A safety would be wired to drop out the contactor. It would not switch compressor power directly.

The simple answer is check power on the Y terminal. If the thermostat is calling for cool then there should be power on Y.

Some compressors have a protector that directly breaks line voltage. They may cycle as the compressor cools, restarts, overheats and trips again.

 

[LS6 Tommy]

Some compressors have a protector that directly breaks line voltage. They may cycle as the compressor cools, restarts, overheats and trips again.

That's the Internal Overload. It senses both temperature and current draw.

Tommy

 

[hal1]

Yes, yellow is secured.

Post #14 & #15 seem to describe the symptoms. My unit could run perfectly for hours, day after day, as I 'super-cool' the house (Time Of Use energy savings here). Then, sometime it just seems to randomly shut off for 15 minutes. So I guess te short question is , have you guys seen what's in post #14 before? Is it typical.

 

[BD1]

Is your condensate draining properly ??
Some units have a condensate sensor in the evaporator pan.
It will shutoff condenser .


Sent from my iPhone using Tapatalk

 

[hal1]

Is your condensate draining properly ??
Some units have a condensate sensor in the evaporator pan.
It will shutoff condenser .


Sent from my iPhone using Tapatalk

Well, the overflow safety pan (whatever you call it) is clean and dry (the staining you see seems to be very old, maybe when installed?. I'd assume it's flowing out regular conduit, but it's so dry in PHX that there can be days when the A/C is running and nothing comes out the outside drain anyway. - current humidity - 8%

I'm guessing I can pour water down that vertical piece? But that wouldn't tell me what's happening in the system before that junction.

As I mentioned, it rarely exhibits the problem, but it is noticeable when it does

 

[LS6 Tommy]

Yes, yellow is secured.

Post #14 & #15 seem to describe the symptoms. My unit could run perfectly for hours, day after day, as I 'super-cool' the house (Time Of Use energy savings here). Then, sometime it just seems to randomly shut off for 15 minutes. So I guess te short question is , have you guys seen what's in post #14 before? Is it typical.

If the compressor's internal O/L was opening, the compressor would stop, but not the condenser fan. If the entire condensing unit is shutting off, it's an auto reset safety or T-stat issue.

Tommy

 

[TRWham]

Just to cover a possibility: are you sure you do not have interruptible HVAC? If the condensing unit shuts down (both fan and compressor) and it's been happening since new, that may explain it.

 

[LS6 Tommy]

Just to cover a possibility: are you sure you do not have interruptible HVAC? If the condensing unit shuts down (both fan and compressor) and it's been happening since new, that may explain it.

THAT is an extremely good point. Is there a "box" mounted between the outside disconnect and the condensing unit? If so, that could be your answer.

I can't count how many times customers asked me to remove those things...

Tommy

 

[hal1]

THAT is an extremely good point. Is there a "box" mounted between the outside disconnect and the condensing unit? If so, that could be your answer.

I can't count how many times customers asked me to remove those things...

Tommy

Where would that be, what would it look like?

 

[TRWham]

Where would that be, what would it look like?

Probably a device (a box of some sort) in the power between the unit disconnect and the condensing unit. It would likely have a PoCo label or some indication it belongs to them. You would also see some indication on your power bill that your billing plan includes the feature.

ETA: post a photo of your condensing unit and the electrical for it and we might be able to help find it- if it's there.

 

[hal1]

So that box on my condenser just has the honeywell name on it.

Also, how about this idea to test the t-stat......

Hook a small 24v LED from the "C" to the yellow. If the t-stat is working the light will be lit - whether or not the AC is running. Then, when I notice the AC shut off randomly, the bulb will go off if the t-stat is bad?

 

[firebirdparts]

I think you're all answering my question - that it shouldn't be randomly stopping before reaching the desired temp.

I don't design new thermostats, but the old ones, you could easily understand how they worked, because you could see it all.

Old thermostats were "compensated" by devices you could actually see. Normally this is called a "heat anticipator" but they also had anticipators on air conditioning that worked in reverse. That is, they were deliberately designed to shut off before the set temperature was reached. The people who designed them believed they could hit the target just perfectly, and they could avoid overshooting the setpoint, if adjustment on the anticipator was provided, and if you used that adjustment to get it just right. That's just part of the way they were designed, and this goes back many years, maybe forever.

I don't take any responsibility for the one you have now, but I just wanted to let you know that there is such a thing, and that it's purposeful. On a digital thermostat, you probably just have 2 or 3 settings for the anticipator. Like "high" and "low" and maybe that's it.

 

[TRWham]

That Honeywell box may be the culprit. I think it’s the demand control device your PoCo is using to shut off your unit. Check your bill for any indication you are on a demand control program.

 

[elderstarr]

What thermostat is it?

If it's a newer Honeywell thermostat, go into the installer settings and disable "Adaptive Intelligent Recovery"

It's their advanced anticipator setting.

 

[hal1]

What thermostat is it?

If it's a newer Honeywell thermostat, go into the installer settings and disable "Adaptive Intelligent Recovery"

It's their advanced anticipator setting.

Emerson sensi

 

[hal1]

It really sounds like a thermostat issue. It'd be real easy to check with a meter.

When it shuts off but is still above the set point check to see if you have power on terminal Y.

The yellow and the common, right? I thought of this But to get to the terminals I have to pull the thermostat, would I still be getting power between the yellow and the common with the brains (t-stat) disconnected?

Along the same lines, I had 2 other similar ideas....

place a 24v bulb between the common and the Yellow and place the thermostat back on. The light should be constant, but the when the unit shuts off prematurely see if the light stays on or not? If it goes off then an indication of a bad thermostat? - or - I removed the backup AA batteries, now when if the units shuts down early, the display will turn off if it's a bad thermostat?

Or are neither of those good ideas, since if it's a break in the power prior to the thermostat it would be the same no light or no display?

 

[LS6 Tommy]

Emerson sensi

That's why I asked what t-stat you have.

Sensi's have a "cycle rate" setting for diffierent types of equipment. The choices are "slow", "medium" and "fast". If it's set to "slow", you'll have wider swings in indoor temp. "Fast" may cause short cycling, but the indoor temp should have least temp swing. "Medium" is usually for ducted HVAC.

Tommy