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  1. #1
    Join Date
    Dec 2004
    Posts
    13
    I have a 1989 central air unit with model number 38TH030310 and serial number 3889E20459.
    Could anybody tell me how to determine the tonnage of this unit.I think it is 2-1/2 ton but am not certain. Also was there any SEER rating at that time and if so, is that also coded in the model no.
    I tried the Carrier website to no avail.
    Thank you.

  2. #2
    Senior Tech Guest
    1989 2.5 ton...10 seer I think but not sure.

  3. #3
    Join Date
    Feb 2004
    Posts
    2,597
    1989

    28400 btu

    8.7 - 9.1 seer

  4. #4
    Join Date
    Nov 2002
    Location
    VA
    Posts
    296
    Preston's Guide rates it @ 8.7 SEER and 28400 BTU's / hour. However with age those numbers fall off... Coils lose contact surface due to clogging and compressors lose ability to achieve full compression. BTW: You certainly got your return on investment... Expected life of residential equipment is indeed 15years at best, though I'll serviced units over twenty five years old that were still completely operational... Oldest refrigeration unit service run I've ever known? My mother's dehumidifier went 51 years before retiring!

  5. #5
    Join Date
    Dec 2004
    Posts
    13
    Thank you all for the information. I bought the house last year and have no experience with the unit, but I estimate from the 1100 cfm and 17 degree differential about 20,000 BTU/hr cooling with an indoor temp of 78 and an outdoor of 90.
    However, the current draw was 12.5 amps (RLA is 16.9), which at .9 power factor (I don.t know what pf these units operate at), I get 2.475 KW. The net COP is then only 2.36, a far cry from SEER of 9. I just had the unit charged. Tech did it without thermometers. Do you pros think it is undercharged or what? Is it time for a new unit/ If so, what are your recommendations? BTW, the cost of electricity here in southern Connecticut is an astronomical 16 cents/KWH.
    Again, thanks for your responsiveness.

  6. #6
    Join Date
    Apr 2003
    Location
    Eugene, Oregon
    Posts
    1,209
    The charging method you describe would not fit the bill for accuracy however, is their a charging chart still attached to the unit? If no info is available to the tech that may explain his/her method.
    Proud supporter of Springfield Millers and Oregon Ducks.

  7. #7
    Join Date
    Feb 2004
    Posts
    2,597
    Originally posted by millerman
    The charging method you describe would not fit the bill for accuracy however, is their a charging chart still attached to the unit? If no info is available to the tech that may explain his/her method.

    even if no info is available, you STILL need a thermometer, just to make sure there is SOME SH/SC.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,876
    Originally posted by skzekeman
    Thank you all for the information. I bought the house last year and have no experience with the unit, but I estimate from the 1100 cfm and 17 degree differential about 20,000 BTU/hr cooling with an indoor temp of 78 and an outdoor of 90.


    That would be the sensible heat btu, that doesn't include the latent btu.

    So you unit is doing better then you think.

    It may be time to upgrade to a 13 seer or better, with your electric rate.
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