One of my customers has a 3700 square foot house, probably 1000 square feet upstairs. The upstairs AC runs continuosly and the area will not get cool. Outside might be 85 and it will be 81 up there, worse when hotter. The attic is vented and the rooms insulated up there.
The only thing that I can think of is that the cool air goes straight down the stairs and the hot air from downstairs, rises into the upstairs.
Any experience with this and what can we do?
Replies
Close the dampers on the first floor.
1. check AC to make sure temp is correct. temp coming out of the vents should be around 60 degrees. (I am assuming you dont have a thermocouple to probe the air just above the fan?)
2. check to see if vents and doors are open because if the thermostat is in the hall and the doors are closed it will take forever for the cool air to reach it.
3. that being said I had the same problem last week and everything checked out and I couldnt figure out the problem. Answer- the switch that turns the heat element on had malfunctioned and was heating the air at the same time it was cooling it. Temp out of the vents was in the 80's. I replaced the switch and problem solved. So check it out it may be........... especially if there is no other obvious reason for the problem.
-worth exactly 2 cents!
So, the cold air is not going down the stairs and the downstairs hot air coming up is probably not the cause of this???If it was, I was thinking of putting in a door at the top of the stairs.Nobody is as good as they seem, nobody is as bad as they seem either.
Edited 4/30/2007 12:16 am ET by handymanvan
you are thinking of convection currents in the atmosphere, I dont think it works fast enough indoors to affect the ac. Check the amps on the wire leading to the heating coil- mine was the emergency heat strip. Like I said, if none of the obvious things are affecting it try that. It just sounds alot like what I just went through.
This is helpful, I am going back to check, anybody else have anything possible?Nobody is as good as they seem, nobody is as bad as they seem either.
Back to my cheap suggestion. I used to have the exactly same problem. Closing the vents downstairs made all of the difference and gave the same temps up as down.
The house has an upstair unit and a downstairs on separate thermostats, which vents are you saying to close? Return air, or just the outlets???Nobody is as good as they seem, nobody is as bad as they seem either.
Edited 4/30/2007 9:39 am ET by handymanvan
"The house has an upstair unit and a downstairs on separate thermostats..."
Then I'm sorry for interjecting. That wasn't mentioned earlier. Forget I said anything.
Hmm, Upstairs and Downstairs on separate stats.
Ok, for the upstatirs installation, how is it ducted? Through an uninsulated attic, and high-wall or ceilng registers? Or, is it floor/low wall resgisters?
Who sized the HVAC systems? Was it a retrofit? Why ask that? Well, sometimes the "rep" from the HVAC contractor is good, soemtimes not. Rule-of-thumb can make for some dumb plant sizing, sometimes.
You mentioned attic venting in the original post, is that a "whole house fan"? I'm guessing that it is, since you said it made things warmer. That's not terribly surprising, as it will "take" the warmest air "first" and then try to push that air out of the attic venting (note that the fans are often way beyond most attics' ability to vent, cfm v. cfm).
What may be needed, just maybe, I'm only a voice on the internet 3000 miles away, is a zoned stat system, that can run either system as needed. May also be that the return air needs to be combined, so that the upper unit is drawing from cooler "warm" air in the a/c cycle.Occupational hazard of my occupation not being around (sorry Bubba)
My house is configured the same way and I live in eastern central florida on the coast. I have a two story 1600 sqft under air and I love the divided systems. I am curious to see what the result is and how its corrected though.
I would be interested in discovering the age of the unit, mine is approx 20 years old and most of the switches have been replaced.
Could be something as simple as a dirty condenser unit, not enough to trip it on high head pressure, but enough for it to run constantly. A low charge and frozen coil can also produce the same simptons.
Dave
A low charge and frozen coil can also produce the same simptons.
Yeah, that was a thought I had, too--but I decided to presume that it was a working pair of systems, if only to decrease the number of variables to consider.
My real fear is that OP is getting solar gain from the structure, or from unshaded windows, and he's fighting wall surfaces that are radiating heat along with all the warm air in the house climbing to the top of the covective column.
Next worst case would be "ducts optimized for heating" so the supplies are low and the returns high--least best in a/c season (thus the question to OP about the orientation of such things).
It's also why I'd like to know if OP meant powered attic ventilation versus a "whole house fan," too. "Encouraging" the hot air in the attic out might help; trying to pump a few hundre CFM air into the attic might not.Occupational hazard of my occupation not being around (sorry Bubba)
Yep. Suspect low refrigerant charge on the upstairs unit.
Also, poor seasonal startup can cause problems. People who seasonally cut power to the condensor/compressor need to realize that the unit needs power for awhile to evaporate refrigerant before activating the thermostat.
Jeff
If the house is well-sealed and well-insulated there shouldn't be that fast a movement of warm air/cold air. Something else is going on. Is there cold air coming out of the ducts upstairs?
All of the answers so far are possibilities. The trouble is that it could be one of many, many (did I say many) problems.
Basically in laymans terms, hot air rises and cold air drops. Cold air is heavier than hot air which is why usually you need to speed up the fan for a/c mode. Hot upstairs and cold basements are always a problem with a/c so your customer's problem is not uncommon.
I guess the first question I would always ask "is this a new problem or has it worked okay before?". If they have never been satisfied then you probably have a design/install problem which has got worse due to the normal things that happen. Maybe there is a design/install problem that only seemed to be working okay and in fact was never working well. A quick example of design/install problem : a bungalow has the ductwork running down the centre of the house with feeders running off to separate rooms.We like symetrical don't we. In the winter the cold walls are on the north and west side so shouldn't we have more heat going to that side of the house BUT in the summer isn't the heat on the south side greater. Shouldn't we have more cooling on that side? Do we have a problem? You betcha.
Maybe the neighbour just cut down a huge tree beside your customer and now there is a huge heat gain on that side of the house.
As I said, many, many possibilities.
good luck
roger
Friends of mine bought a house, which exhibited similar symptoms that stumped a few repairmen. I wasn't in on the fix, but somehow when the A/C came on, the thermostat called for heat, and they got hot air through the supply vents upstairs. It was toasty upstairs!
I am going back over there to check all of this out. This house had no attic ventilation---builder just did not put anything in--I just installed four turbines--eave vents already in place. I think that you all have hit the nail on the head with the low freon--dirty coil deal. The return air vent is also in the ceiling and the vents, in my opinion, are for sure in the wrong place--leaveing a decent portion of the rooms to fend for themselves. I have a feeling that I am about to find marginally insulated ducts as well. I should go over this week and I will post here on what I find.
The homeowner recently bought a home warranty so I can not send my usual, always reliable AC guy over---might go when the warranty guy goes--I will print and carry these "suggestions" with me to help solve the problem. I think the rooms have always been uncomfortable but now it is HOT.
Guys, it turned out that the culprit was low freon. I thought it was something else because she had already had two service calls from an AC company. Thank you all for your help, I will not forget some of these responses in the future.
let's hope so. I could write a book on the number of times service guys say it was low in refrigerant. I would be in the book also.
roger