Hi all, 2015 is turning into the Summer of Never Ending 90+ degree days this year in west GA. My 14yo Ruud UAKA 024JAZ AC unit was running all afternoon cooling house to 78 with these 90+ temps. Had a tech check system and everything is good, system running as designed.

I know it can't be good to expect the system to run continuously so I got a 6000 BTU LG window unit for the living room to act as a "helper" or "booster" unit for the afternoons. Setting the house therm at 79 and running the LG at 77 on med fan speed seems to be keeping house cool and allowing both systems to cycle on and off during even the hottest part of the day.

This seems to be working for me but was wondering if anyone had any other solutions for this problem they've had success with?

My house system is probably a bit under sized for 1300 sq ft vinyl cladded house that gets full sun. My sister's house has same series AC that is actually 2 yrs older than mine but a 2 1/2 ton vs. the 2 ton that mine is and her system still cycles on and off during hottest part of day. Her house is slightly larger(same construction type) than mine but also has some shade on it. Her system was checked same time as mine and no problems either.

These Ruud's seem to be good units. I replaced the run/start capacitor(fan side failed) and contactor(buzzing bad) on hers last fall and both of mine proactively but no other work has been needed so far.

 

Your solution seems sound to me. When the time comes to replace your A/C unit, you might want to consider a two stage unit. It has two cooling capacities, so you can run the smaller capacity for "normal" days and keep the humidity down, and have some "reserve" capacity for those 90+ days. With a single stage unit (what you have now) if you size the capacity to handle the hottest possible days, you'll find that it won't run very long on normal days, leading to higher than desired humidity levels.

 

The flip side to dealing with heat gain (or loss) is the evaluate your home. If yours is in basically good shape insulation wise, then an aggressive evaluation of air leakage, duct leakage, and more insulation could reduce your cooling needs an impressive amount.

Bud

 

I wouldn't worry about it running most of the day, they are built to do that. If the outside temp is at or above design temp, for your area, then it is going to have long run times. What is the nearest big city? I will look up the design temp.

 

Old single pane or even older double pane windows?
Attic and basement or crawl space been air sealed and the right amount of insulation?
Recommended Levels of Insulation : ENERGY STAR
Checked the doors for air leaks?

 

Thanks for all the replies. I'm near Atlanta in beautiful Newnan. The house was built in 2001, double pane vinyl windows, R30 pink blown in attic, R19 batts in walls. I think contractors go a little small when spec'ing heating/cooling for these houses. It's the original system.

I like the idea of a 2 stage system but always like simplicity too, are they reliable? Cutting down all the Pine trees(giant lawn weeds) in my west facing front yard puts more load on the AC too I'm sure.

 

Nice home, but was not built to be energy efficient. Air leakage as an example: Your home will lose 1/3 of all of that nice cooled air every hour, ACH 0.35. (ACH is air changes per hour) The R-30 pink in the attic was bare minimum, and there was no air sealing before it was installed. If your ac unit has ducts in the attic, they need extra insulation and air sealing. As Joe mentioned, basement spaces need to be air sealed and insulated.

It sounds like your ac unit is working fine, just a little small. Invest in improving your house and those changes will last forever (heating season as well) and suddenly your ac unit is capable of handling those hot temperatures.

Bud

 

Thanks Bud! I'll look into that.......in the fall when its not 100+ in attic,lol! Is this something the average homeowner can do himself? What tools/equipment would I need?

My heating system/air handler is all in the attic, house built on a slab.

 

Although ac in the attic is popular in the south and with slab homes, experts say that is absolutely the worst place to locate it. But that's not going to change. The best you can do is to air seal everything, ducts, ac unit, and attic floor, certainly a DIY project. And certainly better during cooler weather.

Over the next 10 years you may be looking for new shingles. They now offer some that reflect some of the radiant heat. Best to block the heat before you have to deal with it inside.

What was installed for attic ventilation. Passive ventilation is marginal from the start even when installed to recommended levels. Below recommended levels the attic gets hotter than necessary and that is where your ac unit is installed.

There are many who have posted here on the forum who are or have done extensive insulation and air sealing.

Bud

 

Attic ventilation is marginal I'm sure, I think all I have is perforated soffit sections on the perimeter. I installed a powered ventilator on roof of my last house but read somewhere you shouldn't do that if you have furnace in attic?

 

Let's double check to make sure your AC is in good condition. simply take the cold input air temperature, and also the room temperature (or return air temperature) at that time. Are they at least 16 degrees apart ?

 

I'm not following clocert? What temperatures??

I had an AC tech check system with his Buck Rogers gauges and everything checked good. Temps, current draws of the fans and compressor, pressures and such I think.

I was going to pop some gas into the 10yo AC system on my F150 and got to checking outlet temps on it, the center outlet was 45 degrees on a 90 degree day so figure you can't ask for more than that,haha!

 

The difference between input air temp and return air temp is what we called DELTA-T. By using DELTA-T number, home owners can easily check if their AC system is in good condition. Not saying that your tech did not do a good job, just to double check and make sure..

 

OK, you're talking about the temp at the return vent vs temp at a supply register vent?

 

That's correct. we like to see the Delta-T at least 16.

 

Looks like I've got 80 at the return grate and 64 at the register furthest from the furnace/air handler. So that's good?

 

80-64=16, that is good. .

 

A lot of excellent expert post advice; especially Bud9051 on efficiency ideas.

At an indoor 50%RH the temp-drop should be 18 to 20°F; with a much higher indoor humidity 16°F would be okay.

Columbus GA; 2.5% Summer Design is 93°F & 78°F or nearly a high 52% Relative Humidity; do not oversize the A/C!

How low was it getting the indoor %Relative Humidity?
Is the airflow from the diffusers strong enough?

You need to do some simple checks on your system.

Creating 'Important' Troubleshooting Air Conditioning Performance Data Records
It would be wise for everyone to take their own performance readings, to compare my findings later to any contractor's data, of which you need a complete record.

This is NOT a DIY fix; all you need is a good digital air-temp probe thermometer (or mercury; digital reading in tenths preferable) an HVAC Supply might sell you one; and a low cost 'Digital INDOOR Humidity Monitor' > ACU-RITE Digital only $8.94 at Walmart (or over the Internet); Walmart has one at +$13.00 now, may be more accurate? Shows if %humidity is too high/too low or OK. Check to see if it registers the temperature correctly; if not, take it back for a Full Refund.

1) Helpful: condenser 'Tonnage' & SEER Rating of Unit &/or model number: Tons 2-Ton SEER ____

2) TXV or, orifice metering device? ________. Only if U know; not critical…

3) Outdoor condenser’s discharge-air-temperature ___°F
Subtract Outdoor air temperature: __°F

Outdoor Condenser Air-Temp-Split ___°F

4) Need the ‘Indoor’ percent of relative humidity - in the middle of the rooms or, at Return-Air inlet grilles ___%RH
Also, get outdoor humidity from online weather info, etc., & wind velocity list it here. ___%RH; Wind: ___mph
Weather Forecast by Zip Code (your local conditions)

5)Subtract Indoor Supply-Air Temperature __°F
From Return Air Temp ___°F
Indoor temperature-split = ___°F
“Reply with Quote” Fill the Numbers in where the blanks are.
Easy Safe testing of your A/C or heat pump's cooling performance for all forum visitors to use.

There are many ways that these Numbers can help diagnose problems 'so you can call a contractor who will help you reduce your utility bills & protect the life of your compressor' & other valuable equipment.

First, make sure the return air filter is clean.
If you have an air conditioner that was manufactured between 1992 and 2005 it will 'probably be' a 10 or a 12 SEER (though some were higher SEER even back then) R-22 refrigerant units.

When the temperature reaches around + 80°F outdoors and the indoor temperature is 80°F and the relative humidity indoors' is around 50% Relative Humidity the outdoor condenser temperature split should be around 19 to 20°F above the outdoor temperature. Airflow CFM differences make less split-differences.

If the indoor temperature is 75° and the indoor relative humidity is 50% then the air discharge temp-split off the condenser should be around 16 to 17°F. A higher indoor humidity= higher condenser split.

With the indoor relative humidity at 50% the indoor temperature split between the return-air & the supply air grille closest to the air handler should be a 18 to 20°F temperature drop with either an 80°F or 75°F indoor temperature. This is also the indoor split with the higher SEER units at 13 SEER or above.

In case you want to do a FREE load-calc: HVAC Load Calculation - Maunualj - Whole House Loadcalc

 

Thks Retired.....now I have good excuse to get the new weather station I've been wanting to add RH, I only have indoor and outdoor temp on the little unit I've had 10 yrs.

The idea of "base lining" your system makes good sense for being able to detect system degradation before it goes critical on a 95 degree day.

I have a nice Weston dial thermometer left over from photo darkroom days I use to measure duct air temps. I've always been good about changing filters regularly and use a quality 1085 MPF 3M filter in both our systems.

I'll get the weather station and report back. So far with this extended heat wave, I installed the glass panel in place of the screen in east facing storm door, front is always glass, and closed off a west facing bedroom I'm not currently using. This is in addition to the "booster" LG window unit in living room. House is comfortable up to mid 90's so far. We may see 100's in August!

 

Tomorrow, Wednesday; the 'Heat Index' due to the high humidity will be an ultra high heat-load on your A/Cs...

Those window units tend to short cycle unless U set the t-stat on them low enough to keep them running; they won't dehumidify much short cycling; I never let mine short-cycle.

 

For the afternoons I run the central unit at 79 and window at 77. I noticed the window unit short cycling with them both set the same.