Question for the A/C gurus - New home unit cycles a lot

[jdavidson]

One other ting I forgot to mention in the original post...

When the unit is off, I can hear a humming sound from the compressor area in the unit. What it means, I have no idea. Sometimes it is louder than others and is not a consistent sound. Sometimes I can hear it and other times not. Course with the builder there, it is not present.

When this happens…shut the disconnect off that feeds line voltage to the outdoor unit ( should be mounted on wall very close to condenser )

If sound continues then it’s low voltage thermostat noise ( to be investigated )

If it quits then you really have something going on

[Kingfisher789]

It’s low on Freon because the condenser fan is pooping the bed now that we gave the rest of the story. Might be an easy save.

[bowhntrmatt]

The low hum you are hearing is probably the reversing valve. It stays energized when the tstat is set for cooling mode, even between cycles. As for the short cycling, it could be a few things, but jdavidson is on the right track. When I do load calcs, I account for blinds 50% closed (kind of a guesstimate since you never know). That and a plum empty house can definitely have an effect on cycle times. It could also be a sizing issue, but not super likely based on your description. This exact problem is why I really like multi-stage or variable-speed systems in encapsulated homes, as they can make themselves run longer for better comfort and dehumidification. But my bet is the issue isn't as bad once you load the house with furniture and belongings.

[Huntindad]

When i pulled circuit breaker thing, it still hummed.

The register temps were from about 60 to 63 degrees through out the house.
The return registers were about 74 on average
Gonna read the tstat manual and see what it says

[Traildust]

Where is your tstat located? If it's close to a return air, it could effect the cycling

[Huntindad]

Tstat is not close to a return register.
been monitering system for last 2 hours. It is pretty consistent in that it kicks back on after being off for 5 minutes.
I didn't see a humidity setting or a way to change temperature range on tstat.

[RutnBuk]

When i pulled circuit breaker thing, it still hummed.

The register temps were from about 60 to 63 degrees through out the house.
The return registers were about 74 on average
Gonna read the tstat manual and see what it says

In my opinion your split should be much more than 11-14 degrees in a fully foamed house. I get 17-21 in a regular home with duct runs in an unconditioned attic.

[bowhntrmatt]

That split is pretty low, but it also depends on how you are taking the reading. If you are shooting a laser at the grill, you are measuring the temp of the metal, not the air. I'm betting that the unit may be a tad oversized, which explains the short run times. As for the short off times, under 10 mins is not abnormal and I bet that increases once the home is furnished. If the problem persists after you move in, I would start by having an HVAC guy lower the fan speed to the operational limit. This will lower the sensible capacity of the system a bit and maximize the unit's ability to dehumidify.

[Huntindad]

I think i was holding the gun to far from vents in the earlier temperature readings. I got closer and the temps were lower. User error. It may be, that when house is furnished cycle times be longer.

[Greenheadless]

What does the HVAC contractor/home builder say?

[Huntindad]

I was told by the builder rep that the HVAC tech went out there and said the compressor system was fine, but the tstat had a setting wrong on the return air fan. It was set to on(running) instead of auto. Didn't seem to make a difference.

my biggest concern/complaint is that the system kicks back on after only 5 minutes. I would think the house full of spray foam would stay within the temp longer.

I did not see where I could set the tstat for a temperature range above/below the set temperature. Kinda sounds as though the tstat is too dang sensitive. Being an empty house may have something to do with it.

[Greenheadless]

I would bring it back up if it were me, it shouldn’t be cycling that often, vacant or not, I would assume.

[Huntindad]

update - they replaced the smart honeywell tstat with a dumb one - basic pro home series programmable. Yesterday, it ran a while. averaged 9 minutes run time and 8 minutes off time. Heck, my rent house will stay off over 30 minutes sometimes.

here's the info on the unit if this helps any one...

[Txhunter3000]

I'm pretty sure most people have systems that run similar. I had a 35 year old thermostat on a 5 ton that would have to lose 2-3 degrees in the house before it would cycle back on. I replaced this with a Honeywell Smart stat and it has 1 degree before it cycles back on. It runs way more than it did before. I have tried to find another stat with more than 1 degree and can't find one. I'm betting this is done on purpose to wear out the condensers early.

I'm betting your rent house has an older stat that has at least 2 degrees of temperature loss before it comes back on.

[Huntindad]

Txhunter3000 - the rent house is about 5 years old with the same tstat. On both houses, the tstat temp never changes, least not on the screen. Maybe internally, don't know. I didn't see a way to modify the degree setting before kicks on or off.