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BWLoveland 07-24-2010 04:24 PM

Central AC wont cool below 80 during day
Hello! We have a 3 year old 3.5 ton heat pump for our 1600 sq ft house in Florida. We have never had any problems until about 2 months ago we noticed that it would get up to 81 degrees during the day. We had our regular a/c guy come out as well as one from our home warranty service. Neither could find anything wrong, heat strips were not on, pressures were ok, etc. They both felt that the a/c, even sized how it was, was not able to keep up with the 96 degree tempature and 103 degee heat index. Our regular a/c guy felt that something may be causing it to short cycle which meant that the compressor would not restart for between 5 minutes and 2 hours, so he lastly put on something that would force start it. No problems for a few days, but today, we are back at 80 degrees, and the weather is not as hot due to the cloud cover form Troical Storm Bonnie passing to the south. We have a 3 year old roof and have had insulation blown up into the attic as well. Does anybody have any thoughts? I thought about calling the manufacturer to see if they have any advice...

mikethe ductman 07-24-2010 04:34 PM

What is the air temp at a supply reg. and return grill?
Make sure your outdoor coil is clean.
Make sure the returns are not sucking attic air.
Do you have an attic fan to help keep it cool?
Do you have a box where the power co. can turn off your unit at peak times?

AllanJ 07-25-2010 06:46 AM

Also make sure the interior coil is clean and filters cleaned/replaced.

Can you tell whether the heat pump (compressor) is running a lot or just a little or continuously?

Unusual short cycling could mean the Freon level is low; you need the "system recharged".

beenthere 07-25-2010 07:07 AM

Hard start kit he put on. Covered up the real problem for those few days.

You need someone that can actually check the full operation of the system. And not just look at a pressure reading and guess its charge is ok.

How often do you change your air filter. Could have a dirty coil. And be flooding the compressor. Could be a dirty outdoor coil, and the compressor is getting too hot, and shutting down on its internal thermal protection, when it tries to restart.

Thurman 07-25-2010 07:11 AM

I'm with "mike", did the service man check the air temp as it leaves at least three (3) supply registers at different areas of the home and the return air grill? Did the service people offer to/or even clean the coils of the unit? The temp of the air as it leaves the supply registers is important, as well as the air entering the return duct box. An attic fan to remove any hot air during this oppressive heat wave is essential. Many of us feel share your situation at this time. I have a 3 1/2 ton "Heavy-Duty" unit on a 1960 sq. ft. home which is well insulated BUT--I have had to raise the temp to 76 inside during the hours between 10 A.M.--5 P.M. to keep the unit from running constantly. I don't like to run it constantly--my POCO does. I've gotten used to having it set a little higher at night and use small oscillating fans to help stay cool during this heat wave. Check those temps, clean those coils, put in an attic fan--IF these have not been done. We'll make it through this, then complain of cold weather. David

BWLoveland 08-01-2010 12:07 AM

Thanks for the advice so far. To answer the questions...

Neither one cleaned the coils that I saw, although neither one said they needed it. We change the a/c filter about every 3-4 weeks. Speaking of the filter, when the a/c kicks on, I can actually hear the "pop" from the filter flexing due to the suction in the return. Does this mean that I need an additional return as I have only one? would that help with the effeciency?

We have decided to go with the attic, actually a gable fan, route. Does anyone have any idea on how much difference I can expect this to make, both in cooling effeciency and cooling costs? I live in Florida and this last months electric bill was $485. Again for a 1600 sq ft house with no pool.

Thanks again!

beenthere 08-01-2010 06:06 AM

If your air filter is flexing in that you hear it. Your air filter may be the wrong kind for your return. And your return duct may be too small. Are you using a 3M or other allergen air filter?

Rusty999 08-01-2010 09:09 AM

All solid suggestions. I've been troubleshooting for most of my life. Paramedic for 12 yrs, muscle car & gear head since early teens, etc. Different fields but all the same skill: Troubleshooting. Someone told be early on, when going after a problem, keep asking "what is different now?"
Youve had hot days before and had it work fine, right? Something changed, and it wasn't the weather. You've actually improve things with the new roof and insulation.
It sounds like you have an intermittent issue and that the svc guys haven't been able to catch it "red handed". Intermittent problems are tough, it' like chasing a ghost.
When it happens, take note of a few things:

Does the condenser come on & go off?

When the condenser starts, is the compressor running of just the fan on top? (You can usuall tell by the motor noise, the linset getting cool and moist, like a can of soda on a hot day, also the air coming out of the top should be hot, a good 20 degrees hotter than the ambient air)

When it comes on, your lights probably dim. This is normal, due to a large in-rush curren to get the motor started. It should last less than 1 1.5 seconds. If it is dimming longer or more than once to get it started, there's a problem.

When you say "short-cycling", do you mean it comes on and shuts off frequently, having shortened run cycles, or does it run a long time, shut off and then stat another cycle very soon afterwards (very little down time)?
If you can watch for these things, it can help point the svc guys in the right direction. You can pick up on clues that they didn't get to see when they were there.
Good luck & let us know.

Gary_F 08-02-2010 05:10 PM

Need subcool and superheat information from your tech, benthere is right, checking pressures doesn't cut it.
Also you need 200 sq in of filter area for every ton of ac, in your case that would be 200 x 3.5t= 700 sq in. Get out the tape measure.
$485 for electricity for last month.:eek:.
I live in San Antonio area, have a 2700 sf home with 9.5 avg ceiling height, using a 4 ton 12 seer 15 yr old unit, and my ac bill for June was $66. @ .097kwh, and for July $76., we keep the thermostat at 78.
You definitely have a problem.
Good Luck

mikethe ductman 08-02-2010 05:31 PM

I live with three dogs and my power bill when I use NO heat or A/C is $35

You can cool a 2,700 sq ft home in Texas for $1 - $1.25 a day.


Gary_F 08-02-2010 06:01 PM

$2.20 a day for June, (30 days x $2.20= $66.) $2.45 a day for July, (31x $2.45=$76)
I generally use 710kwh per month when I am not using heat or ac@.097kwh + a flat $22.50 billing charge=$91.00


Gary_F 08-02-2010 06:09 PM

BTW. I live with one woman.
3 dogs put out more heat, I guess

mikethe ductman 08-02-2010 06:30 PM

I take it you have a fridge, water heater, TV, lights............ just like me.
Just that alone cost me a little over $1 a day.
My dogs don't take a bath, watch TV or use the fridge.
So if you have the same as me plus one more person and during the cooling season your bill goes up a buck and some change a day, while cooling a 2,700 sq. ft. house?
In Texas to boot.
I have to tip my hat to you, While the rest of America would love to pay 3,4 or 5 dollars a day to keep cool you have found a way to do it for a buck and some change.
I am in deep doo doo if this gets out.

Gary_F 08-02-2010 06:38 PM


2 fridges, and a wine cooler. 2 tvs, the old type crt, water heater and stove are propane. CFL's for the lights.
I use ceiling fans and tower type fans to create a breeze., making it feel about 5 dgs cooler.
My total bill for June was $155.97, the ac part was $66. (see previous post to see how this was figured.)
BTW I am living on SS, so I watch my pennies.
Believe it or not.:thumbup:
"you have found a way to do it for a buck and some change".,no, it was $2.20 for June and $2.45 for July

I used this website and trouble shot my own system, this guy is a HVAC genius

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