Central AC run time

[JHobbs26]

I just bought this 5 year old ranch style house with finished basement back in January, now that it's hot outside, 100* heat here in Kansas, I'm wondering if my system is right for the house.

The compressor unit outside is a Bryant 561CJ036-F. I have a Lux LTX9000TS-004 thermostat and it gives me current and previous day system run time. Yesterday my AC ran for over 19 hours.

I have the thermostat set at 78* with a 2 degree swing and in the late afternoon it will show 82*, like it cant keep up.

I had a technician out to check everything over, he said everything looked normal, hooked gauges up and washed the compressor unit from inside out.

I know this is builder grade equipment, but should it be running for anywhere between 15-19 hours a day?

[pstu]

I just bought this 5 year old ranch style house with finished basement back in January, now that it's hot outside, 100* heat here in Kansas, I'm wondering if my system is right for the house.

The compressor unit outside is a Bryant 561CJ036-F. I have a Lux LTX9000TS-004 thermostat and it gives me current and previous day system run time. Yesterday my AC ran for over 19 hours.

I have the thermostat set at 78* with a 2 degree swing and in the late afternoon it will show 82*, like it cant keep up.

I had a technician out to check everything over, he said everything looked normal, hooked gauges up and washed the compressor unit from inside out.

I know this is builder grade equipment, but should it be running for anywhere between 15-19 hours a day?

I am a homeowner so what I say is not authoritative. But your AC needs to be able to maintain your chosen setpoint of 78F in order to do its job. I would expect multi-hour run times if sized just to ACCA methods (Manual J, S, etc) but 19 hours on a 1-stage AC I would say is just too much.

You seem to have a capacity vs. load problem, which is likely a malfunction rather than a sizing problem. Lots of AC salesmen are happy to sell you a whole new system, and many happy to sell you a bigger system because the old one is allegedly "undersized". However to really tune and diagnose your system requires a different skill set, and lots of technical skill. IMO you have a problem and the only solution is find a pro who is better than 80% of the guys around here. Until proven otherwise I would not rely totally on the diagnosis of the first pro who looked at yours. Expect the cheap pros and the good ones to be two mutually exclusive sets of people.

In my experience, a system which ran multi-hour run times actually had a bad TXV (Thermal Expansion Valve). Even though it had been maintained by a company with good reputation, they overlooked this. A new pro found and fixed this problem, and now it is clear the sizing is way more than it needs to be -- before this fix I had thought the sizing was marginal. After this fix it barely runs half the time in the hottest of days.

If you do have to think about whether sizing is correct (AC people rarely undersize), never forget that if you improve the building envelope, you reduce the load needs and can use smaller equipment. If any house upgrades are possible, consider those first.

Hope this helps -- Pstu

[54regcab]

I'd most of the forum members are in that top 20% of A/C techs. Hacks/people who don't care if it's done right don't typically visit the forum.

I'd look into why you have so much heat gain, 5 tons is a big A/C.

[CountryBumpkin]

That is a 3 ton unit.

[REP]

OK a couple of things.
First I don't know what your design temps are.If 100 is an unusual high then your unit might be sized correctly.
Second is that if your tech didn't look at the underside of your evap coil then he only did half a job.
I know that I would have really looked at your duct size,the number of supplies and returns.Especially the returns.
You say hye put gauges on,but did he get a temp drop across the coil or supply and return tempatures?
I find it hard to believe that he would leave without solving your problem.You clearly need a better tech to address your situation.

[RIGUY]

what size is the house, what is the td across the coil, what are the pressures, and did you check for loose returns in the attic sucking in 100 degree air with lots of humidity, also are all the supply grilles open??

[54regcab]

That is a 3 ton unit.

My bad, I saw 5yrs and was thinking 5 tons...

[kdebord]

Your problem is not unusual and there is not a simple answer that you will receive here, or anywhere else. There are simply too many variables for anyone to give you a certain answer based on this information alone.
With all that being said (typed), there are some things to consider:
To properly size an air conditioner a heat gain calculation (commonly refered to as a "Manual J") must be run. This calculation takes into consideration all of the construction details of your home. For example: the heat transfer rate of all the materials ("U-value' often expressed in the consumer term "R=factor"); how much insulation; what type, what size, how many, and what direction do your windows face; and much more. In addition your lifestyle should be taken into account.
After all that is done then the correct unit must be chosen - which involve the total capacity and the sensible heat ratio (in other words how much of the capacity does the unit use to dehumidify).
AND all of that can only be computed after the design factors are decided: outside temperature and humidity, indoor temperature and humidity desired. The outdoor conditions are published for your area (and all of the United States - and basically all of the world) along with what percentage of the year those conditions occur. So a designer has to decide what percentage of the time they are designing for - typical is 95 - 98%. The problem is whatever percentage you size for with a conventional single stage unit (like your Bryant) it isn't sized exactly most of the time.
I know it's hard to believe while you're sweating, but over sizing is worse than under sizing, for a variety of reasons.
Also, what you have is a 3ton unit which is nominally 36,000 btu in total capacity. However that is at AHRI conditions - 95degrees. For every degree above that you loose capacity. Also, if your coils are dirty, you loose capacity; if your unit isn't charged properly, you loose capacity. There are other factors that can and do cause capacity loss.
What about ductwork? It is estimated that typical duct systems lose between 25-40% of the heating and cooling put out by the central system. (Don't take my word for it look at websites for: DOE; ASHRAE; ACCE; AHRI) The possible problems with duct systems range from improper design, to improper insulation, to air leakage, and more.

Finally, in 100 degree weather if your system does not run most of the time, there's a problem. Your system could be working properly as designed, but it's just as likely that it is under sized, or has installtion issues. However, as I said at the beginning there is too little information in your post to be able to speculate accurately.

I hope that this wasn't so complicated and long winded that you didn't make it to the bottom.

[AvantGarde]

I just bought this 5 year old ranch style house with finished basement back in January, now that it's hot outside, 100* heat here in Kansas, I'm wondering if my system is right for the house.

The compressor unit outside is a Bryant 561CJ036-F. I have a Lux LTX9000TS-004 thermostat and it gives me current and previous day system run time. Yesterday my AC ran for over 19 hours.

I have the thermostat set at 78* with a 2 degree swing and in the late afternoon it will show 82*, like it cant keep up.

I had a technician out to check everything over, he said everything looked normal, hooked gauges up and washed the compressor unit from inside out.

I know this is builder grade equipment, but should it be running for anywhere between 15-19 hours a day?

Is your house set up to keep you cool?

[JHobbs26]

Sorry for the delay in the replys, here's a bit more info.

I checked the air coming out of the register that is the farthest from the A-coil and it is 65*

Now I'm wondering if this could be an air flow problem and not a refrigeration problem.

[mike_home]

Your condenser and duct work may be undersized. Are 100+ degree temperatures common for your area? If you post your approximate location, one of the Pros can look up the summer design temperature for your area.

How many square feet is your house? How many windows do you have facing south and west? Is your air handler and duct work in the attic? Do you have rigid or flexible duct work?

Answering these questions may help in determining what the problem could be, but ultimately you will need a heat load calculation and duct evaluation.

[motoguy128]

Sorry for the delay in the replys, here's a bit more info.

I checked the air coming out of the register that is the farthest from the A-coil and it is 65*

Now I'm wondering if this could be an air flow problem and not a refrigeration problem.

Of hand, it sounds about right to me. The temps out of the registers aren't too bad since it's so hot outside, although they mean little without knowing the actual airflow. If it's a PSC fan you'd need the fan performance curve and static pressur emeasurement to determine that.

Design temps for much of kansas I'd expect are around 97F. So you're above design temp.

Keep all of your shades drawn and seal any air leaks.

Overall it sounds like it's working OK. The good news, you only have a single 3 ton unit.

[JHobbs26]

My wife's cousin (HVAC tech) was able to stop by last sunday and take a look at my system.

The A-coil was dirty, he cleaned it out real good. He didnt think it was dirty enough to cause my issues tho.

He checked the blower motor capacitor, and found it was drawing too many amps, i think thats right? Anyway he replaced that.

Next, he goes outside to check the pressures at the compressor. My system was almost 20# over charged.

Air temp coming out of the registers used to be 64-66 degrees. After he lowered the pressures, it dropped to 58-60 degrees. I was experiencing run times of 17-18 hours a day, since Sunday i've been averaging around 12-14hrs. and the house stays closer to the 78* temp i have the t-stat set at.

[pstu]

My wife's cousin (HVAC tech) was able to stop by last sunday and take a look at my system.

The A-coil was dirty, he cleaned it out real good. He didnt think it was dirty enough to cause my issues tho.

He checked the blower motor capacitor, and found it was drawing too many amps, i think thats right? Anyway he replaced that.

Next, he goes outside to check the pressures at the compressor. My system was almost 20# over charged.

Air temp coming out of the registers used to be 64-66 degrees. After he lowered the pressures, it dropped to 58-60 degrees. I was experiencing run times of 17-18 hours a day, since Sunday i've been averaging around 12-14hrs. and the house stays closer to the 78* temp i have the t-stat set at.

That is great news, congratulations! It illustrates how wrong charge can reduce your cooling capacity and result in abnormally long run times. I would wager your humidity control was poor too, based on the air temperatures. I hope you will change AC techs to someone equally good as your wife's cousin, and keep him and pay whatever he needs.

Best of luck -- Pstu

[lentz]

Glad you got some good help. When someong knows what they are doing it really makes a difference. Clean coils, a clean filter and the proper charge helps. We are having the most days near 100* that I have ever seen.