# Weak Central Air problem

• posted on July 1, 2006, 1:08 pm
everyone,
Have a problem of my A/C not cooling my home down sufficiently:
Quote: I would consider 30F condenser dT to be the upper limit on older low SEER units, beyond which there is an airflow problem. On the newer high SEER units, I would draw the line at 25F dT.
The lower limit would depend primarily upon load. I would think it should be about 15F dT or above.
Here is the list of temps I use for online trouble shooting.
Low side:
Evap air in temp = 66°F Evap air out temp = 48°F SST (saturated suction temp) - Where is this measured and how? Suction line temp near compressor = 35°F
High side: (I'll get these soon)
Cond air in temp - Cond air out temp SCT (saturated condensing temp) Liquid line temp near condenser
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description of my system:
2 Ton Copeland Hermetic Recipricating compressor (inside a 1987 seer 8 condenser) 1980 Tappan furnace 1953 brick ranch style house, with insulated attic and insulated basement, about 1100 sq ft
Performed a test yesterday with monitoring temperatures becuase it was very calm and stable outdoor air temps today
Outdoor air temp was 81 from 1pm to 5pm Inside air temp started at 76.8°F @1pm inside air temp ended at 75.2°F @5pm ATTIC AIR TEMP was over 103°F during all the hours Every half hour the main floor temp only dropped about .18°F during these hours. Humidity on main floor was 42% at 1pm, and dropped to 38% by 5pm
What would you guys call a low seer unit?
couple more things: the temps that are listed in the quoted text are from my current setup, I just inserted them thats all. I replaced the furnace blower motor. The compressor is new (few days) Basement temp is very close to main floor temp (couple degrees difference(which I think rules out any bad ducting leaks)) AND when the return air is 72°F, the output air from any room vent is 57°F
Are these okay temps? I want my house temps to fall at little higher rate when the system runs. Like for example, it never shut off in those
5 hours as my target temp was 72°F !!!
~Will
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<%-name%>
• posted on July 1, 2006, 1:24 pm
Lin0 wrote:

Basically, what this tells me is that your heat load is too great for the capacity of the unit. More attic insulation might help some plus adding some (more) ventilation or even a power exhaust.
Is the basement finished living space and is it ducted or is it just a basement?
You don't mention how many windows/doors, etc., nor condition of them nor presence/absence of thermopane and/or storm windows. Such losses as that would be another place to consider.
Also, is this an ongoing existing condition or has something changed? W/ the new compressor, I'm guessing the old unit died and was repaired? Probably a better choice would have been a new system although unless the house were brought closer to current-day standards of insulation and leakage control (or has been _recently_), a 50s vintage house will probably be very "lossy"...
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<%-name%>
• posted on July 1, 2006, 2:01 pm
Heres the info you requested: 14 windows Anderson Thermopane with Storm windows currently installed. Great condition.
The basement is finished and I added that into the 1100 sq footage, its got two additional ducts to heat and cool it, both are under 2 feet in total length and are shut for the summer.
The condition started when we had some brownouts back in 1995 and we're just now making the repair on the unit to run again. (weak compressor due to brownout) We've been just using an attic fan in the summer for the last 10 years.
Attic is insulated R19
Any tips on finding losses? I went and bought a no-contact temp gun last night.
Thanks so much! dpb wrote:

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<%-name%>
• posted on July 1, 2006, 2:18 pm
EDIT My Temps dropped .4°F PER HOUR sorry bout that Lin0 wrote:

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<%-name%>
• posted on July 1, 2006, 3:02 pm
Lin0 wrote:

Actually, I overlooked that -- that's really not too bad.
As noted, w/ the air temperature at the duct outlets you have plenty cool enough air so either you have to move more air or reduce the heat load.
The thing I forgot to look for specifically and when I did look in your description is the house construction. My guess is right-BRICK. Brick houses are terribly difficult to cool once they're hot owing to the high heat capacity of the brick--it just keeps on radiating into the living space even after out of the direct sun. In that age of house the amount of wall insulation is minimal at best and possibly might not have been if it was a tract house. There's where I'd start looking and of course, only a few air gaps can make a big difference. Plus, shade to minimize the solar heating of the roof and brick veneer can make a significant difference.
The other thing that can make a big difference in overall comfort is to leave the fan on and use ceiling fans to keep some air movement.
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<%-name%>
• posted on July 1, 2006, 5:41 pm
Cool take a look at these temps and see if the current insulation is doing its job
Right now 1:31pm Flat Rock michigan = 84°F My A/C is not on, and there are no fans bringing in outside air 79°F on main floor 104°F in attic All outside walls ranging between 76° and 81°F 100% sunny and 1/4 of roof is in tree shade
I'll reply back sunday night as I am leaving to Lansing. Be back, and thanks for everything! =)
dpb wrote:

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<%-name%>
• posted on July 1, 2006, 11:42 pm
Lin0 wrote:

I'll bet you would see a noticeable change if you were to add more attic ventilation

How did you measure that? Surface temperature measurement is difficult and not necessarily very accurate owing to whatever the surface actually is.
But, what's more important is the difference between the inner and outer temperatures which is nearly nothing at that point in time -- that indicates more likely that it simply hasn't warmed up that much yet but _could_ also be saying there essentially isn't any thermal barrier-- impossible to tell the difference from only one data point even assuming the values are correct.
The only thing that makes think you would likely have at least some is that you're in a northern cold-weather climate where I would _presume_ they routinely did insulate. But, not knowing anything about the particular house, that's still simply supposition--a lot of tract houses were built around that time in a real hurry and energy saving at the time was _way_ down on the list of priorities.
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<%-name%>
• posted on July 3, 2006, 1:19 am
dpb,
I bet I would also BUT I want a floor up there sitting ontop the rafters. So what I will do is look for a high R value insulation that is the thickness of the rafters up there. If anyone has any suggestions, I'td be much appreciated.
I measured all the INSIDE walls on the outside of all the rooms with a laser temp gun/no contact gun. I also shot the roof and on the northwest roof it was 85 - 90° and shaded by a tree on the southeast roof it was 120°F throughout
I'll take some readings of the inner and outer temps tommorow around 1pm, thanks for the great suggestion!

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<%-name%>
• posted on July 3, 2006, 11:22 pm
I'll get them readings tommorow, it rained and was cloudy all day here. Lin0 wrote:

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<%-name%>
• posted on July 8, 2006, 4:32 am
Nevermind about them readings now. I pulled my A-Coil and cleaned it. The difference?
Before the cleaning, the system dropped the house temp at a maximum .4°F an hour. Afterward, it dropped at 1.65°F an hour minimum. In the room that counts the most (my room) it was able to do 2.1°F an hour!
I used a fine wired brush to get the crap off the bottom of the coil. I used my air compressor to blow out the fragments. And I finished up with Frost King Coil Cleaner, from Lowes. So yes, fiberglass filters friggin suck. I'd rather use a higher Merv filter and save the time and headache from pulling that A-Coil out and cleaning it every 6 years. The filter I am switching to is Merv 7, washable filter. That way I'll just clean it every month, and save the money and waste.
A large thanks to everyone whom made suggestions and took part in my thread.
Lin0 wrote:

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<%-name%>
• posted on July 1, 2006, 1:25 pm
http://forum.doityourself.com/forumdisplay.php?f 6
ATTIC AIR TEMP was over 103°F during all the hours Every half hour the main floor temp only dropped about .18°F during these hours. Humidity on main floor was 42% at 1pm, and dropped to 38% by 5pm
What would you guys call a low seer unit?
couple more things: the temps that are listed in the quoted text are from my current setup, I just inserted them thats all. I replaced the furnace blower motor. The compressor is new (few days) Basement temp is very close to main floor temp (couple degrees difference(which I think rules out any bad ducting leaks)) AND when the return air is 72°F, the output air from any room vent is 57°F
Are these okay temps? I want my house temps to fall at little higher rate when the system runs. Like for example, it never shut off in those
5 hours as my target temp was 72°F !!!
~Will
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<%-name%>
• posted on July 1, 2006, 10:19 pm
I'd sure like to know the operating pressures. The suction line temp helps to get the superheat. First two things come to mind, check the airflow through the evaporator, and clean the condensor.
--

Christopher A. Young
You can\'t shout down a troll.
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<%-name%>
• posted on July 2, 2006, 2:41 am
For a point of reference. My AC drops the inside air from 80 to 60 (outside it was 84), there is a steady stream of water coming from the system. My system works fine. Too high a delta T is inefficient, too low gives poor dehumidification. Note the incoming Freon line (smaller line) is barely warm to the touch. If your system is not similar to this something is amiss. If it is then it may be too small for your home.
ATTIC AIR TEMP was over 103°F during all the hours Every half hour the main floor temp only dropped about .18°F during these hours. Humidity on main floor was 42% at 1pm, and dropped to 38% by 5pm
What would you guys call a low seer unit?
couple more things: the temps that are listed in the quoted text are from my current setup, I just inserted them thats all. I replaced the furnace blower motor. The compressor is new (few days) Basement temp is very close to main floor temp (couple degrees difference(which I think rules out any bad ducting leaks)) AND when the return air is 72°F, the output air from any room vent is 57°F
Are these okay temps? I want my house temps to fall at little higher rate when the system runs. Like for example, it never shut off in those
5 hours as my target temp was 72°F !!!
~Will
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<%-name%>
• posted on July 3, 2006, 1:26 am
Jeff,
My incoming is barely warm to the touch.
And at 40% humidity, my system does not "stream" water out of it, more like a rapid drip. thank you very much for the thoughts! =) Jeff wrote: