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Byron Trantham
06-29-2007, 8:40 AM
We are having problems with our AC. The compressor (2.5 ton carrier about 17 years old) is outside (of course) and the air handler is in the attic. We just had the techs out and the freon is OK, plenty of heat coming off the cooling fan outside all-in-all a clean bill of health. Here's the problem, it doesn't cool. The outside temp is 100 degrees and I bet the attic is closer to 170 degrees. Is it reasonable to expect to cool a house to say 72 degrees when the outside is 100 degrees? If the answer is no then I am confused because we have been using this thing for 17 years with the same kind of VA weather and haven't noticed a problem. Can the system get a clean bill of health and still not handle this kind of temperature differential? I forgot to mention that our system is a duall zone sytem. The unit downstairs works fine but is newer as it was replaced about 3 years ago. The compressor failed. They are not trying to sell me a new unit. I did ask about new ones and they said I would be getting a SER (sp?) 13 unit which physically larger than my current unit. HELP:o

Randy Denby
06-29-2007, 10:06 AM
Check the return air temp and the supply air temp....Use an accurate thermometer and check the return air temperature at the return air grill. Check supply temp at the closest grill to the air handler. Should be an 18 to 21 degree drop. Check duct for any leakage /breaks. With the age on the system, compressor could be losing compression capabilities.....it has a piston and ring similiar to auto's. Are the coils clean? sorry....alot of questions and I gotta run....I'll check back in tonight

David G Baker
06-29-2007, 10:28 AM
I do not know about air conditioners but I do know that you need to vent your attic. If your attic is 170*, in my opinion, that is a problem in its self. Proper attic venting can lower your home temperature by quite a bit and reduce the load on your air conditioner. Keeping your inside temp at 72* when the outside temp is 100* should not be any problem for a properly functioning air conditioner. Also check your insulation to make sure it is adequate for your area.
When I lived in Northern California I would turn my unit on in the early morning to pre cool the house so the unit wouldn't run as much in the afternoon when it was really hot out. There were many days of 110* temp and it was not a problem to maintain a 72* inside temp. My house was insulated but not that well.

Michael Weber
06-29-2007, 11:16 AM
Had a similar problem some time ago. Losing almost 50% of my AC capacity due to attic heat and leaks in the return air supply. measure the temperature of the air at your return air vents and then in the air handler just before the coil. With no leaks, they should be about the same. With leaks the temperature just before the coil may be many degrees higher. As stated earlier you should get about a 15 to 20 degree drop across the coil but if the temperature into the coil is 100 degrees because of leaks, then obviously that won't work. Find the leaks and vent your attic if possible.
In my case the leaks were due to openings in to framing top plates used to frame out the closet my unit was in. The vacuum created by the blower motor in the bottom return air space below the unit was drawing super hot attic air down through the wall cavity. The top plate opening were for gas piping and electrical. You could actually feel the sheetrock get hot on that wall. It was a really poor installation.
Mike

Ken Garlock
06-29-2007, 12:19 PM
A couple thoughts:
Are your filters clean?
Have your ever cleaned the evaporator coils?
Have you ever balanced the air flow at the registers?

If the techs said the freon is OK, then the compressor is running OK also. Checking the freon level is a matter of putting gauges on the output and intake of the compressor and checking to see it the pressures are within an acceptable range. Also, if the freon is low the compressor will cycle on and off frequently. In a tight system, you should never had to add freon.

jeremy levine
06-29-2007, 12:21 PM
If you have an inline air filter, make sure it is clean and the acess to it seals well.

Byron Trantham
06-29-2007, 12:22 PM
Some good questions. First the roof was just re shingled (strip and replace) our roof vent is all along the peak plus the contractor added (without my asking) more vents along some dormer peaks. The temperature that I stated was a SWAG. I have no idea what it is really. Our house has 2x6 exterior walls with insulation. We also just replaced all the siding with vinyl. Plus they installed 5/8 foam board completely wrapping the outside walls and taping all the joints, which already had that stuff called blue board (I think). I think we're as insulated as you can get. I just talked with the AC folks and I think they are thinking the same thing that one you pointed out - IT'S 17 YEARS OLD! Interestingly enough today is much cooler than yesterday and the upstairs is nice and cool. The unit is cycling as expected. I guess it just can't handle the extreme heat/humidity combination. I will try make the temperature measurements suggested here. Thanks for you input.

Byron Trantham
06-29-2007, 12:31 PM
A couple thoughts:
Are your filters clean?
Have your ever cleaned the evaporator coils?
Have you ever balanced the air flow at the registers?

If the techs said the freon is OK, then the compressor is running OK also. Checking the freon level is a matter of putting gauges on the output and intake of the compressor and checking to see it the pressures are within an acceptable range. Also, if the freon is low the compressor will cycle on and off frequently. In a tight system, you should never had to add freon.

Ken, good points. We are religious about changing the filters. The evap coils are clean and our air distribution system does not have dampers. The large grey flexible hoses go to each register. I can turn on a register or turn it off. That's about it. The Freon level is fine as it was just topped off about 4 weeks ago and when he came by yesterday he recheck the levels and they were fine. We do have a leak in the evap coil though. Small pin hole I'm thinking. Frankly it looks like I will limp along until next March or so and have them install and end to end system.

Lee Schierer
06-29-2007, 12:36 PM
I agree with the other post, but need to add one more thing. If you had service guys out to check the system, why didn' they do a complete job. They should have checked the inside air handler too. If the air wasn't flowing or the coils were plugged they should have discovered that for you since you paid for a service call. I would suggest you give them a call and ask them why it isn't cooling. If they did in fact hook up pressure gauges which is the right way to check the freon charge, then they should also have seen if the compresoor was working. If the compressor was working then the evaporator coil should be getting cold. There aren't any moving parts in the system.

Assuming nothing has changed insulation and air flow wise in the attic you should get the same cooling you've had other years. Clogged air filters or coils will limit airflow and in sufficient air flow will imit the cooling capacity.

When I lived in Charleston SC, I installed roof vent turbines on the attic in my house. They made a world of difference and cost nothing to operate. Installation was a pretty easy DIY job.

Pat Germain
06-29-2007, 2:29 PM
I used to live in Southern Virginia. Attic fans are your friends. :) Seriously, I know many people who installed an electric fan in their attic and got amazing results. I had the old-fashioned oscillators on my house which didn't work nearly as well. The electric fan is installed against a vent, typicially directly under the point of the roof. It has a thermostat wich is typically set to turn on when the attic temp is above 80 degrees. Yes, that means they run almost all the time in the summer. However, they actually save energy by keeping your AC from working so hard.

The fan pushes hot air out and pulls in cooler air from another vent at the opposite side of the attic, thus reducing the temperature significantly. These fans are easy to install, but do require an electrical connection; typically easy to find in a attic. They also help to reduce moisture buildup in your attic and are sure a lot cheaper than a new AC system.

Randy Denby
06-29-2007, 5:26 PM
Ok...I'm back.
Someone said.."If the techs said the freon is OK, then the compressor is running OK also". Not that easy. Its like saying your car run's so the engines ok. Having 5 -10% percent blowby thru the rings/valves on the piston/ head will affect capacity .Sure, it'll make the suction alittle higher than normal and head pressure a little lower......but unless the tech checks superheat and subcooling, he aint gonna catch it. Just reading pressures alone wont get it.

They need to do a full system analysis.
1. Check subcooling, superheat on the refrigerant side. Since it sounds like you've had an ongoing leak, this will also tell if you have any non-condensibles in the system.....happens when a tech doesnt bleed his gauges before charging, pushing air into the system.Will also prove blowby or drier problems.
2. Check for any temperature drop across the filter/drier...should not be any drop otherwise the drier is restricting refrigerant flow. This must be done with a clamp on thermometer as doing it by feel/touch will not accurately tell.
3. Check entering air temperature (return) and compare it to leaving (supply) to verify an 18-21 degree drop across the coil.. Once taken, this should tell them to look at dirty coils, mixed return with attic air, etc.


Finally...an a/c systems biggest load , up to 70%, is removing moisture out of the air (latent heat), then it starts dropping the temperature (sensible heat) as the moisture is removed. So... high humidity is the biggest load, and with all the rain we've had here in Texas and around this area, its making most a/c's run overtime.

Ken Garlock
06-29-2007, 5:50 PM
Randy, thanks for the correction and good information. At 17 years, it could be a blow-by problem?

Randy Denby
06-29-2007, 6:05 PM
Ken, no problem. I hope in my trying to explain stuff, I dont come across as a know-it-all.Cuz, Lord knows.....I dont.:o And yes it could be blowby at that age, heck they all start degrading from start up. It depends more on hours of use than years old I reckon.
FWIW...Ken, I have thought to myself...alot of times, after reading your posts, I have got to reply to Ken Garlock as I very much respect your opinions . I didnt mean to single anyone out....just meant to clarify a misconception I see by pro's even.The refrigerant pressures are read taking into consideration...the outside temp, inside temp,efficiency of a unit, coil cleanliness (evap and condensor)etc. Alot of variables..so some techs just charge a system somewhere in the ballpark....not taking into consideration that a slightly off reading is actually blowby and not just a little low or little high pressures . Why I suggest a full analysis...not ballpark charging for times when everthing should be right but aint.I always take temp readings as wll as pressure readings....it saves on callbacks. And I really hate those...its embarrassing as well as costly.I gaurantee our work and will make it right even if I go in the hole.Our reputation is most important
Take care. Randy

Tim Wagner
06-30-2007, 1:13 AM
Get some other evaluations done also. just to make sure your freon is really ok.

Ken Garlock
06-30-2007, 1:31 PM
Randy, you embarrass me. Thank you for your kind words.

In a lot of areas, I have enough knowledge to just get by, and hopefully enough to not be snookered by a fast talker, or cause damage.

As an aside, I had a Water Furnace geothermal system installed when we built. The evaporator is a Trane unit with a Honeywell microprocessor control for 3 zones. Guess what has failed? The Trane evaporator got a leak and had to be replaced. One of the Honeywell servo dampers quit working. The evaporator was under warranty, but those darn servo damper cost an arm, and a leg. Since then, I have found them at just 20% of what I was charged. That repairman, was quoting his company price, but he sold me two of them at once: the first and last!:mad: Otherwise, he has been a good service man.

Have a good 4th.:)