3 Ton Lenox Single Stage AC sounds like it is possibly short cycling

uuacallis

New as of last last September but since it is as hot as the sun out right now getting them it to look at it is like 2 weeks out. So- want to ask the experts what you think

System is Lenox single stage with a honeywell panel to control the two zones. I noticed looking at my Sense energy monitor that it turns on and off every 5-10 min all day long. When the temp on our third floor is reached I hear the thermostat click and then I hear the fan slow down and can hear the compressor sound like it is shutting down only to come right back on for a second or two before shutting off. I checked and all three dampers (2 control second floor, one bigger one for 3rd floor) are opening and closing properly and when it is on we get cold air.

We have been having issues with it being hot on second floor but believe it's related to poor knee wall insulation.

Thoughts?

Mike

Have you checked the return air filter? It must be clean for good air flow. Sounds like the low temp limit is shutting down the compressor. A dirty air filter will cause this.

uuacallis

Yeah, actually the second thing I checked and I even swapped to brand new ones despite my belief the ones I had were clean.

The space being conditioned is a finished attic (~800-1000 sq ft) and our second floor about 1000 sq ft.

It's a three ton unit that cannot keep up on some days (as in we get no air flow at all) and then on other days is on and off every 10-15 min.


My gut tells me it's something with the zoning panel but I am not sure how to prove it.


> @Mike said:
> Have you checked the return air filter? It must be clean for good air flow. Sounds like the low temp limit is shutting down the compressor. A dirty air filter will cause this.

JUGHNE

Is anyone familiar with that Sense system. Is it recording calls by the tstat or when the contactor is actually energized?

Could be a low on charge or a plugged TXV causing shut down on low pressure. Not uncommon but an ordinary t-stat would not see that short cycling.

uuacallis

It is only recording spikes in energy consumption. I may be calling it the wrong thing when I call is short cycling. I see the energy consumption spike of the AC (correlated to hearing compressor from my home office) so I know it's the AC.

I was planning a test tonight when my wife can be near register on second floor and son can be by one on third and I can be by the compressor outside - essentially turn both zones down to say 68 to make it stay on.

Measure the CFm (subjectively) by noise and paper flap when it kicks on and see if it slows down over time. Then shut down one zones call for cold and see if it increases air pressure in other zone. In theory it should but as I recall from the hot evening the other night it didn't.

It's almost like a variable speed fan that is slowing down and then when it reaches set point I will listen to see if compressor actually shuts down or makes that weird sound where it sounds like it is going off then right back on for like 5-30 seconds before shutting down completely. If it were a heat pump i would think defrost.

uuacallis

Ok - here are the components involved

Lenox ML193UH Furnance
Lenox CX34 AC Coil
Lenox 14ACX Compressor

JUGHNE

So your sense system only sees things starting and stopping.
Your Tstat or zone control might tell the comp to come on and stay on. Outside in the unit are safety controls that can over ride that call from Tstat. High pressure cutout.....if the outside coil is plugged with cotton or lint.....or outside fan fails after starting.
Low pressure cutout......low gas in unit or it is pumping down because of restriction in liquid line going into house, as mentioned plugged TXValve. After about 10 minutes pressure comes up and AC starts again for a few minutes....then off for maybe 10.

Could this condition existed previously and is only noticed now that the temps are really up? I had 104 in NE today, don't know what you have. This could have been half-**** cooling until today?\

First cooling season and they can't get to you....must be hot there.

Mike

The zone panel controls your equipmentbasically tells it to come on, and when to shut off. The compressor should never shut off then be allowed to come back on right away. That needs to be addressed. Sometimes, you have airflow, sometimes you don't. Is this with both zones calling? Some where you have a bypass damper. This is usually the problem, not being installed properly, or it's getting hung up, stuck open. When only one zone is calling, it opens to relieve the excess air . Three tons of air going to a ton and a half zone is pretty noisy. If not installed properly, and the ice cold bypass air is dumped back into the air hander with a cold coil the unit should shut down on freeze protection. Then restart in 5 minutes. Check to see if that's operating freely. With both zones calling how is the airflow? The bypass damper should be completely closed.

uuacallis

I agree it has bee half **** cooling. Because of the high efficient system they were originally pulling direct outside air in 80% humidity and all so when it was 97 outside (San t was today) it could only get the house down to around 84-85

When they swapped the two ton for a three ton compressor outside they also sealed that vent from ourside which helped significantly, but alas today it had a hard time holding 75. I could live with that, I guess, but what doesn't make a let of sense is why after running for 10 min when it meets the target temp I hear the compressor go off, back on, then off each and every time.

uuacallis

> @Mike said:
> The zone panel controls your equipmentbasically tells it to come on, and when to shut off. The compressor should never shut off then be allowed to come back on right away. That needs to be addressed. Sometimes, you have airflow, sometimes you don't. Is this with both zones calling? Some where you have a bypass damper. This is usually the problem, not being installed properly, or it's getting hung up, stuck open. When only one zone is calling, it opens to relieve the excess air . Three tons of air going to a ton and a half zone is pretty noisy. If not installed properly, and the ice cold bypass air is dumped back into the air hander with a cold coil the unit should shut down on freeze protection. Then restart in 5 minutes. Check to see if that's operating freely. With both zones calling how is the airflow? The bypass damper should be completely closed.

Thanks I will double check, however from all indications there is no dump dampener. Just three total (on two zones)

Z1 has two wired together and Z2 he just one.

EBEBRATT-Ed

Sounds like it was installed in September and maybe they never really did a proper start-up, did you see any hot weather to test it out last year??

Sounds like a control issue or shutting down on freeze stat.

HVACNUT

There should definitely be a barometric relief on your system.
Is it the Honeywell True Zone panel? Are there wires connected to DATS?
The system might be shutting down from the Discharge Air Temperature Sensor. Is Purge enabled? The thermostats should have a factory default 5 minute delay to prevent short cycling, unless it was reprogrammed to 0 minutes. Sounds like a lot of things need to be addressed, especially since you can't get the temp down below 84*.

Mike

Sorry I missed a post or two. 2 tons for 1800-2000sf, with outside air? When you got upgraded to 3 tons, was the indoor coil and furnace changed also?

JUGHNE

This post was just getting interesting....hope he responds back with outcome.

Big Ed_4

When the temp on our third floor is reached I hear the thermostat click and then I hear the fan slow down and can hear the compressor sound like it is shutting down only to come right back on for a second or two before shutting off.

As mentioned the zone control board controls the outside condenser .. There is also an built in timer not to let the condenser cycle back on with in 10 min. .. I would be checking that board