AC ISSUE - http://www.hvacmechanic.com/ Forums
Original message
| bjw
 |  "AC ISSUE"
, posted Thu 14 Aug 13:30  
Had new Carrier Comfort 3.5 ton, seer 13(inside & outside units) installed for about 1550 sq ft home late April 2008, Houston Tx area. Didn't seem to cool as well as old unit & late May when it started getting hotter noticed was running long periods in afternoon, and couldn't seem to lower from 80 to 78. (normally run at 74-75 from about 10 pm to 8 or 9 am & 80 remainder of day). Tech sealed some areas missed but still wasn't working correctly. Then all duct work replaced with new & R8 installation. Still no better. Then replaced evap coil inside - stil no better. Then replaced condensor outside - still no better. Then ran new suction line to pull out hot air. Still no better (actually not as good at night as it was). Takes about 3 hours to cool from 80 to 78 in afternoon & is running over 1 1/2 hours just to maintain at 80. Electric useage is way higher than last summer for same period when we had unit that was 10 years old. Tech has run tests with air monitor on temp & relative humidity & says RH is ok. Any suggestions of what could be wrong? Is there anything else in the unit that could be bad? Is it possible to just have a "lemon" unit? Our old unit was a Carrier Comfort also & worked great. Help!!
Thanks!
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Replies:
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| envirosystemtec
|  "Re(1):AC ISSUE"
, posted Sat 16 Aug 12:01:
turning the a/c lower then what it can do will freeze the evap coil normally a/c units can only cool 15 to 20 degrees below outdoor temp if it 100 degrees outside set the stat to 80 and see what happens
dont think you have a lemon bad company not explaining the operation call another company you nice equipment ask them to chech the metering device is it a 'n' coil
tim
[this message was edited by envirosystemtec on Sat 16 Aug 12:06] |
| Jojo98
| "Re(1):AC ISSUE" , posted Thu 14 Aug 22:03
If you have the suction and head pressures, superheat or subcooling temps. that would help. You want 1 ton of refrigeration per 400sqft of living space. You are slightly undersized, but the unit should still cool. Measure the air temp. at the return grille and the supply register nearest the AHU. You should have approx. 16 to 20deg split, if the A/C is properly charged and moving enough air.
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| TIMDECKER
| "Re(1):AC ISSUE" , posted Thu 14 Aug 14:58:
Yes, definitely a parts hanger. I have installed many 3.5 ton 12 seer units in houses that are 2300-2400 sq ft with temps never going over 75 in the summer. These houses had Tech shield radiant barrier on the sheathing and double paned windows. The filter drier should be taken out of the system after 30 days but no one ever goes to that trouble. Sounds like you may have excessive air in the system. Best bet is to call someone else to do a complete system check, obviously you are in need of someone who is trustworthy and experienced. This type of person can be found at your local community college. I know Todd Marxsen, he was one of my instructors, could surely do the job and show you what is wrong with your system. He works for Excel Air. You may have a freeze up in the evaporator from the high humidity.
Greetings from Houston TX the AC capitol of the world!
[this message was edited by TIMDECKER on Thu 14 Aug 15:23] |
| | Jojo98
| "Re(2):AC ISSUE" , posted Thu 14 Aug 21:52
High humidity will NEVER cause an evaporator to freeze up!
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| obxtech
| "Re(1):AC ISSUE" , posted Thu 14 Aug 14:21
Sounds like you have a parts changer not a technician, First off a heat load calculation should have been performed on the house then ducts and equipment sized according to that calculation. Don't know why he has changed so much just to find out why it is not working. He can take several readings and calculate the capacity the unit is putting out. Does he even know what the CFM is running at? none of the above repairs make any diffrence if your unit is not sized properly or your air flow is not properly adjusted. I would call some one else out to check the system.
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