A/C Slow to cool

Hi all,

I had some hvac guys out to do some reapirs as part of my home warranty. They said the unit is on the small side for the house, and that they would suggest looking into a new unit (due to unit condition). I wanted to get your input based on the below if you agree with this assesment, and whether a new unit would fix the poor cooling.

Hvac reapir guys found the capacitor to the outside unit to be blown. Air filter is new, coolant levels are good, ac fins are clean, and the evap coils are clean. Despite all of this I still find that my central air is taking a long time to cool. For example it ran for 3-4 hours the other day and cooled 1 degree. I realize the cooling 1 degree could be normal if humidity is high, and items such furniture, flooring, etc... may radiate to some degree to counteract the cooling.

Some observations:

• Unit is 11 years old
• All cold air returns except one will hold a piece of paper
• Cold air intake temp is around 76 degrees
• Most floor vents have weak output, and can only be felt from a coulpe feet away. The strong vents can be felt from 3-4 feet away
• Air temp inside of vent is 55-60 degrees
• Air temp 1 foot above vent is ~70 degrees

Thanks!

 

Your temps sound just fine (actually common is about 16-20 degrees) but it seems like your airflow may be weak. That could be why the temp split is so high.

3-4 feet away? I can feel mine 10 ft away, lightly of course...but I can definitely feel it like walking in front of an open refrigerator.

Has it always done this..or just since the original problem occurred?

 

We moved in end of Summer last year so minimal usage and as such I don't have a gauge. I did read the temp differential should be 16-20, and you should feel it from 8 feet away. I did have the blower motor replaced this past winter, but it was replaced with the same size, 3 speed with AC is wired to high, heat to medium.

 

Well...I'm no Pro....but if you provide type, size and construction of home along with model numbers of inside and outside units....they may be able to help.

A good company will measure the airflow from the outlets...of course the warranty company didn't, right?

And why should an 11 y/o system be replaced? Well, by the warranty companies thinking...because they get paid very little for service calls, but a system replacement would come out of YOUR pocket.
I find it hard to believe anyone would live in a house for 11 yrs (pre-you) where the A/C didn't work that well.


Oh...and can you give a correct location? For whatever reason your IP shows NY but you listed OH.

 

House is a two story, 2500sq foot, full unfinished basement, wood framed, double pained windows, vinyl siding with brick front. I am not sure on the insulation used during build.

Warranty company sent a local hvac company out, but I plan on calling them again...just want to be more prepared this time.


AC is a Bryant 561CJ024A
Furnace is Bryant 383KAV
Blower motor is 10587

Located in Columbus, Ohio

Thanks for the replies!

 

Columbus OH 2.5% summer design is 90F dry bulb, 73F wet bulb & 44% relative humidity.

A 2-Ton on 2500sf; it better have a perfectly sealed duct system, & sealed home, to keep air infiltration as low as is allowed; otherwise it will have a low sensible ratio & ultra long runtimes.

Also, the airflow being too low will greatly reduce Btuh output of the system.

You need a Home Energy Efficiency Audit & Click> Load Calc performed on your home so you know what to do to improve your home's energy efficiency.

 

2 ton seemed small to me too, and the repair guys said 2.5 may be better but even then it appears a proper load calculation is needed. Now I wonder how I can get the home warranty to cover.

 

I ran a whole house calc using total guesses on most things.

Walls R-13; ceiling R-38; tight ducts & tight home Air Infiltration at a low .375-ACH that yielded 125-CFM. (You can make these things TIGHT.)

The Tech there may get a lot higher Btuh load-calc.(?)

Total Cooling 21,617; Sensible 17,374; Latent 4,243; Heating 35,556.

At those conditions, the 2-Ton will only produce 21,550-Btuh Total; 16,917 Sensible; 4,633 Latent.

On this totally inaccurate 'input' load-calc, the 2-Ton is low on Total & Sensible, just above on Latent.

This is meaningless; but wonder how far off it will be from a 'fairly accurate input' load-calc.(?)

I am thinking a 2.5-Ton would be a better match to your home's heat-gain, even when the ducts & home is tightened up...with the 2.5-Ton unit you could use 350-CFM per-ton of cooling when conditions are extra humid.

Wait & see what the Tech's load-calc shows.

If you go to a 2.5-Ton system, the duct system may need to be enlarged or use more Supply Air runs to diffusers, & use 2 Return Air filter grilles with deep boxes to the duct entrance.

Keep the static pressure at .5" WC or lower.

 

Prepare yourself for a big disappointment. The warranty is to fix existing systems and equipment. If un-fixable then maybe they would install a larger system if you paid the difference. Just because it may be too small for the house isn't their problem. I'd think that would have been something caught by a good home inspector, though most would just check to see if it functions.

 

Thanks guys, this information helps quite a bit. I'll get some estimates on new A/C units and have them do a load-calc. As for the home warranty I figured they would not cover if the ultimate cause is the unit is not sized right, but I am going to try.

From having a larger AC would I expect the air that's being pushed to be colder? I assume so since the actual air flow is controlled by the blower and and vents.

 

Just to say again...no Pro...but your temp splits (Delta t?) seem fine...but the airflow seems very low to me.

They have a little device with a fan blade that can calculate the amount of air flow through the vents.

Many times a system may be perfectly adequate...but bad installation of ducts will decrease it's capacity.

Had a new home built in VA...was never really satisfied with the cooling , but I was working and wasn't home during the day and often gone for months at a time (Navy).

Eventually found they had never sealed the bottom of the air handler to the A/C coil inclosure. Can you say massive air loss to the attic? Also installed a quality Honeywell stat which made a huge diff.

 

The temp-drop is largely controlled by the amount of humidity that the indoor coil has to condense.

However, you may be able to operate 2.5-Ton at a lower 350-cfm per-ton of cooling, or 875-cfm, which could result in a little colder airflow; @90F outdoors, 75F & 50% humidity indoors, the 2.5-Ton would be delivering around 24,900-Btuh.

Remember; you want a Scroll compressor & a TXV on the indoor coil; don't settle for less.

Once again; Remember going up in tonnage may not make much difference if you don't make sure the Supply air & Return ducts air are sized large enough, or you have more of them, with plenty of filter area.

The ducts need to be sealed with mastic brushed on all the joints; & your home needs to be sealed from air infiltration down to near .375 Air Changes per Hour.

If you get a quality install & everything down right, you'll notice a big difference in performance.

 

You would probably have to have a very well built house with lots of shading (or north exposure) for a 2 ton unit to cool 2500 sq ft.

Odds are, you need 2.5 or 3 tons, and the duct system needs to be able to handle the required airflow.