A/C working but having cooling/flow problems - http://www.hvacmechanic.com/ Forums
Original message
| ojmisc
 |  "A/C working but having cooling/flow problems"
, posted Tue 6 May 15:26  
I've got a 3 ton Trane a/c unit that produces about 20 degrees difference from return to supply. I measured this by inserting a thermometer at the return and then setting same thermometer into the various supplies throughout the house. Once my A/C system comes on it basically stays on till evenings when everything cools down. I have a 1/3 HP blower motor set up to use the highest speed possible for cooling. For heating system works fine. Contractors just want to replace the HVAC system with a new one. I think my system is working just not putting out the cold air that it has inside. My system's return is 128 sq inches - while the supply is 364 sq inches - Is this imbalance my problem? Can I use a faster blower fan to overcome this problem? What to do?
Thanks!!
|
|
Replies:
|
| Freon
| "Re(1):A/C working but having cooling/flow pro" , posted Wed 7 May 13:21
3 tons needs ~1,200 cfm of air flow. Your return filter area (assuming filter grilles) should be ~600 sq in. You need to tell us each supply duct size to determine the supply cfm capability (6" duct= ~120 cfm, 8" duct = ~240 cfm etc). But from the little so far, it seems you have a system with too little air flow. Improving air flow should improve cooling capability.
|
| Jojo98
| "Re(1):A/C working but having cooling/flow pro" , posted Tue 6 May 22:19
20 deg. split is pretty good. Try cleaning the condenser.
|
| acefurnacefxr
| "Re(1):A/C working but having cooling/flow pro" , posted Tue 6 May 18:35
sounds like its under sized.
HVAC REPAIR IS NOT A DIY WEEKEND PRODJECT
I have been performing HVAC repairs for 23 years
http://www.hillaryclinton.com
|
| | ojmisc
| "Re(2):A/C working but having cooling/flow pro" , posted Thu 29 May 15:50
The house is roughly 30x50 two levels - basement and main living space - HVAC is center in the middle. Most of the vents have been closed in the basement. The house had a fire back in 95 and was rebuilt professionally - all HVAC components including airways were updated. The house built in 1956 is a hybrid house - metal construction on top of a wood frame in the basement -insulated in the walls and attic.
I moved in 02. Previous owner had already modified professionally the HVAC system to try and bring in more cool air into the kitchen (without success) I added a small two story extension of 300 sq in total - with own air supply.
Last Summer on the first hot day - started the AC up and just started getting hotter and hotter - system wasn't even keeping up. I had it - called in the 4 different professionals - they only wanted to sell me new units and not service what I had. My gut told me that the system was overall working due to the temp differences between supply and return and cold air was at the registers it just wasn't "getting out". I put this story to the techs and asked why a "new" system would do any better since my old system seemed to be working.
Only one tech mentioned the potential air imbalance between supply and return - I even got a boost in cooling when I closed off by 50% two supplies just outside my distribution box with their dampers! I couldn't get to the other damper - all behind drywall - for now.
I don't know how to translate sq inches into CFM capability but sizing is below.
MY distribution box is basically a rectangle on top of my HVAC system. The two original supplies are 16 x 8 (128 x 2 = 256 Sq inches)and run about 25 feet each way they get reduced in sizeabout half way down. The run into my addition is about 25 feet also and is 9 x 12 (108 sq inches). There is also a 8 inch round that was run into my kitchen for the extra cooling that doesn't work.
The return is at the top of the steps about 15 ft away and feeds a 16 x 8 (128 sq inches) run into a 24 x 20 return box attached to the HVAC system - there is also a 8 inch round that's taped into the basement for additional return air.
The system is fully charged with freon, ducts were cleaned, indoor air coil/heat exchanger was physically removed and fully cleaned (original owners used wrong size filter - what a mess). A clean blower motor is 1/3 HP - 1075 RPM, 4 speed - with fastest speed for cooling.
The system is a Trane all sized, picked and installed by professionals when house was redone - I'm not sure if all the components "match".
How do I increase my returm to 600 sq inches - my air filter is 16 x 25 (400 sq inches)?
If I get a bigger HVAC system won't it be limited by the same airway problems?
Can my distribution box somehow not channel the air into the supplies? Do I just cut a large hole into my "return box" to increase air into the HVAC system itself? I'm really confused on how to fix this.
Thanks all.
Thanks!!
|
| | ojmisc
| "Re(3):A/C working but having cooling/flow pro" , posted Mon 9 Jun 13:44
How does one find a good HVAC design person in the yellow pages? Any suggestions I'm in tbe Northern VA area.
Thanks!!
|
|
|
|  |
|
