Originally Posted by scottmcd9999
Trying to cool a 2 story home with a single unit is not easy. There's always zoning, where you install electric dampers to control the differents areas (or "zones") of your home. Those zones would each has a tstat, and you could maintain each zone at the desired temperature (for the most part). That said, retrofitting ductwork to handle a zone system can be very, very difficult, especially if your ducts are enclosed in walls, floors, etc.
I have not found this to be a problem. Properly sized ducts (supply/return) and matching air handler size to the ducts / heat load will correct this. Additionally, the use of jump or transfer ducts helps also.
so what could be the issue.
my guess from 4000 miles away...
1. air handler / tonage way to big for the building or to big for the ductwork. Lots of people and contractors like to think bigger is better, in fact the HO in this thread said "may I need a bigger system". Bigger is not better. bigger leads to short run times on the hot days and does not allow the air to circulate. This the "fix" of keeping the fan running all day. Note that this idea is not economical as the ducts may be picking up heat load and or leaking. The leaks may create a negative pressure in the house and cause additional heat load...
2. static pressure. if the returns are too small or restrictive filters are used, the speed of the air in the system is slowed. if the volume of the air in the system is slowed there is no mixing of the air and of course heat rises and the upper floors get hot. The supply side ducts could be too small for the air handler. Typically the installers will slow the fan to reduce the static pressure, whic leads to low air speed and low volume.
so what do to?????
first off check your delta t. The Delta t is the temp of the air comming into the air handler and the temp going out the other side. you may need to drill a small hole in the ducts (NOT THE AIR HANDLER!!!!) to insert your themometer. 15 to 20 degrees difference is what you are looking for. higher (like 30 or 40) means the air is too slow... lower (like 5 or 10) means that the air is too fast.
Next thing to check is the static pressure of your system. Use the same holes and use a manometer (fairly cheap on ebay). You want one what will measure up to about 2 inches of water. Analog or digital, its your dime, so pick what your comfortable with.
next thing to check is the air speed and volume at each of your supplies. use an anemometer for this (again cheap on ebay). be sure to get one that does cfm and air speed (fpm). also check the returns for FPM. This should be less then 350 fpm. Check with and without the filters.
so until you have the tools, what can you do... caveman testing!!!!
first off, get a feel for how much air is pumping out of the registers upstairs. just use your hand or tie a piece of yarn to the registers (i use yarn, med weight, 1 foot and some tape.) run the system and see how far the yarn moves. Now remove all the upstairs registers. run the system and feel for any difference. Re-tape the yarn if thats how you are checking. My guess is that you will find a larger volume of air moving through the opening. All registers are not created equal!!! some are restrictive and some are not.
next, with the registers off, remove all the filters in all the returns. run the system and check the air flow up stairs again. My guess is that it will be much better.
shut down the system and open up the air handler service door and take a look at the evap coil. Is it clean or dirty (dust hair etc). Now run the system with the doors open (there may be a switch that will not allow this, defeat that switch). Re-check the upper floors. My guess is that you will have more air flow.
so what have we found???? my guess is that you do not have enough returns and your registers are restrictive and maybe your coil is dirty. My guess is also that your delta t is high, due to static pressure or low air flow.
How to fix it?????
1. caulk around the registers. This will stop any air from leaking into the walls/ floors. Mastic the seams of the ducts, as far as you can reach. this will help (in a small part) to keep the air in the ducts. its easy to do and since you have the registers open anyway!!! just do it!!
2. mastic up the return seams and into the return as far as possible..same thing as above.
3. Research better flowing registers. replace the upper floors. I have found that registers with flow dampers are not so good. Adjustable bar type registers are good. None of them are cheap!!!
4. research air filters. retrofit your system with 5 inch media filters.
I think (4000 miles away), you will find some improvement with these suggestions.
but get the tools and check yourself!!! After the air flow issues are fixed, read up on subcool and superheat in order to be educated when you call a professional to check your system for refrigerant levels!!!
good luck and report back what you find!!!!!