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Perplexing Central AC problem

Posted by krnbk2 (My Page) on
Wed, Jun 8, 11 at 16:53

I am in need of some assistance, hopefully you folks can help me out.

I recently purchased a house with central A/C and radiant in-slab heat. My air handler for the AC system is located in the attic of my house (house is a ranch. 2,000 sq/ft)

Problem 1: I appears my system has developed a leak. Dealing with my home warranty (american home shield) has be less than ideal as the hvac contractor they hired appears to be unwilling to actually perform a leak test. They have been out twice in the last week to fill the system with freon. The last time they were out they also replaced a schrader (sp?) valve as he said this was the likely location of the leak. As of now, the system appears to be holding a charge but I am now seeing a new problem.

Problem 2: During the middle of the day my the AC does not adequately cool down the house. At night though the AC works exceptionally. I have taken measurements with an infrared thermometer and this is what came up with:

Middle of the day
Return: 78 degrees
Closest vent: 74 degrees
furthest vent: 78 degrees

Return: 75 degrees
Closest vent: 60 degrees
Furthest vent: 60 degrees

My question is why does it appear my system works well at night but horrible during the day? would low freon be the cause?

Something I read on another forum was that if your attic temperatures are too high and your air handler is up there than it could be saturated with heat. I just found out this morning that my roof mounted attic exhaust fan is not working. Could this be the problem?

Sorry for the long post, I'm just at my wits end and want the AC to work. Please help!

Follow-Up Postings:

RE: Perplexing Central AC problem

" I just found out this morning that my roof mounted attic exhaust fan is not working. Could this be the problem?"


RE: Perplexing Central AC problem

what are the daytime temps on the day when the unit was only cooling to mid-70s inside?

Systems are designed to perform at a typical temp range , and not usually designed for the hottest temp of the summer. For example, where I live, units are sized for 95 degree outside temps. But it gets over 100 from time to time. On those days, the system won't be able to keep up and keep a house cooled to 72. But since that is only a couple of days per year, the cost/benefit is designed to give you proper cooling about 95% of the time.

So if it has been REALLY hot lately where you live, that MAY be the problem.

RE: Perplexing Central AC problem

The roof exhaust fan will help bring down the temperature during the day, but it is not the real solution.

I don't have experience with attic installed equipment, but I suggest you inspect the insulation of the attic duct work. It sounds like during the day the attic is getting very hot and you are getting no cool air through the vents. But in the evening the attic cools down and temperatue differential goes up to 15 degrees.

RE: Perplexing Central AC problem

mike_home, this weekend I will check the insulation surrounding the ductwork.

I mentioned the roof exhaust fan because I thought that when working it probably lowers the attic temperature a bit and by doing that I was unsure whether it would make a difference in how well my system can move cold air.

Juliek, I live in New Jersey and current temps for the last 2 days have been well into the 90's. Today my area hit 97 degrees and the house was unable to maintain a temperature below 78 degrees with the system running most of the afternoon.

ionized, Would you be able to offer any more insight as to why an exhaust fan would make no difference? I dont not believe you, I am just trying to gain as much knowledge as possible.

Thanks for all the help guys!

RE: Perplexing Central AC problem

Attic ventilator fans often cause problems. If there are not adequate intake vents and leaks between the living space and attic, they suck a lot of cool air out of the living space into the attic. It is a good way to cool the attic at the expense of warming the living space.

RE: Perplexing Central AC problem

That Dave guy just started showing up. Hey Dave, it's great you give people a company they can call near them but how about trying to give them a little help first?

Considering your description of the problem and the temperature differentials you indicate, I suspect a low charge. If previously, the refrigerant leaked out and the unit kept running, it most likely pumped oil, reducing the inside diameter of the lines. Once the unit was charged, the oil worked it's way back into the compressor and now the unit is low on refrigerant. Either that or you have another leak. Of course, an over charge of refrigerant would cause the same problem.

RE: Perplexing Central AC problem

We had the same problem. Between 3 & 7pm when the sun is most shining on the house the temp in the house would rise to 80F.
As soon as the sun was off the house, it would cool down very quickly to about 75F.
Our unit was 18 years old and the evaporator coil was clogged and rusted. We replaced the evaporator and condenser and now the house will maintain 75F no matter what the outside temp is.

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