A/C repair people can't seem to fix prob in new house

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  #1  
Old 08-18-00, 10:46 AM
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I just bought a new townhouse. My thermostat is a programmable Honeywell. The thing is, from about 4 in the afternoon to almost 8 p.m. the AC will not go below 80 or 79 degrees.

I realize the AC may have a problem cooling when it's real hot outside, but I'm just trying to get it to 75. I've had the HVAC people out four times and they say there is nothing wrong with the system or the thermostat. Can anyone tell me if this is normal? - I get the feeling they don't want to be bothered because it's a warranty item.
 
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Old 08-18-00, 12:15 PM
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Here is a brief true story. My neighbor and I had central air put in both our homes the same year. My contractor, added new intake and out going duct work because the house was built for heat only, thus it needed more ducts to handle a/c. My a/c works great!!

My neighbors contractor did not add any new ducts and had the same complaint you now have, ever year. There house has been sold twice over the years, each time, the new owner calls the a/c service people when it gets 90 degrees outside. In short, my neighbors house has undersized a/c system and will never cool properly.

Mark
 
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Old 08-18-00, 03:08 PM
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Hi suziq:

When you say new, do you mean new construction or new to you? I assume new unit because you mentioned warranty. Are there other units your size by the same contractor in your neighborhood? Maybe you could make some comparisons. An air conditioning system that will maintain adequate comfort levels starts with a room by room heating/cooling load survey. The survey tells us how much heat and moisture has to be removed from each room in the Summer and how much heat has to added in the Winter. From here we calculate for each room that X cfm of air at Y temperature is required. With this information, the ductwork is sized and configured. Then the equipment is selected. All too often some of these steps are left out or guesstimated. Go to the contractor and ask for their design conditions. Most load surveys are based on 97-1/2 % weather conditions. Extreme weather conditions are thrown out because you would otherwise have oversized equipment. Often, overcoming inadequate comfort levels involves increased insulation, better windows, ventilating the attic- things like that. Ask the a/c guys to show you the results of their checks. If you have a 17 to 21 degree split between the return and supply air from the cooling coil on a day when the house is 80 inside, then the a/c is doing all it can do. If it's overworked the split may drop to 16 degrees. It sounds like you simply don't have enough capacity for when it's real hot outside. If you will post your location, I can tell you what the design conditions are and you can tell if you are experiencing design days or extreme days. Thanks. John.
 
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Old 08-19-00, 09:10 PM
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Suziq.......Get a second opinion from a non-biased company. The only reliable heat/cool survey is one that is done after an on site inspection and takes all conditions into consideration. Just a little monkey wrench about the 17 to 21 degree theroy......put an obstruction in the air flow and you have your 17/21 split. Put a leak in the supply line (sucking attic heat) and you have your 16 degrees.
 
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Old 08-22-00, 08:30 AM
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Hi. Thanks for the help. I'm in Kennesaw, Georgia - about 25 miles NW of Atlanta. The house is brand new. It was built in June. I've spoken to my neighbors and they told me I'd have to have the AC guys out at least three times before they fixed the problem ( I guess they don't connect the AC up until someone moves in - but mine was connected when I moved in).

The past couple days it's been cool so I've had no problem getting the AC to 75. Here's what the AC guys did tell me:
The Freon levels are fine
There's a 15 degree difference from what's coming into the house (but he said that's normal?)
I wondered if there was somthing wrong with the thermostat itself - but they said they only got a 2 degree difference.

I have a year warranty with this company. But maybe I should just pay for a second opinon - so to speak?
 
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Old 08-22-00, 04:13 PM
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Hi Suziq:

The industry standard indoor design temp for Summer is 75 degrees coupled with either 55% or 50% Relative Humidity. 70 dgrees indoors is the standard for Winter. The Summer outdoor design temperature for Marietta is 92 with a medium daily range at 19. If designing for 55% Relative Humidity the grains difference is 27 and for 50% RH it's 34. The Winter outdoor design temperature is 21. These numbers are arrived at by looking at weather data over a long period and then taking 2-1/2% of the extreme temps and humidities and tossing them out. If you design at the extremes, you wind up with systems that are oversized all the time which results in poor comfort conditions. The daily range is the average difference between the daily high & low temperatures for a given location. During the night, structures in a high daily range location will cool down faster than if located in a low daily range area. The daily range comes into play when calculating heat transfer multipliers for different types of construction materials. The grains difference is the difference between the actual moisture content of the indoor and outdoor air. The a/c both cools and removes moisture. The lower the desired RH inside, the greater the a/c capcity. That's just some background on how heat/cool load surveys are configured. All too often someone pulls numbers out of the air; like 3 tons for a 1200 sq. ft. house etc. I'm curious to know if they read the 15 degree split on a cooler day or a hot day. On a cooler day, the a/c has less heat load to contend with and the split will be greater. A 15 degree split is barely acceptable on a hot day; on a cool day, no way. I think your idea of a second opinion is great even if you have to pay for it. Have them check the Freon charge closely according to the charging charts in the outdoor unit. You also want them to record outdoor temp & relative humidity and indoor temp & realtive humidity. Start keeping a log of outdoor & indoor temperatures and time of day. You don't need to buy an expensive thermometer, but don't buy the cheapest. When taking an outdoor reading, make sure the sensor isn't in the sun.This at least will give you some ammunition to confront the builder with. Matter of fact, shop around for another company and tell them the problem and what you need. If you get a guy that comes out and just puts on the guages, you won't get a accurate assesment of the refrigerant charge. Let us know you make out. Thanks. John. BTW- in case someone tries to snow you, the numbers I quoted are from ACCA Manual J. They'll know what it means.
 
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