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  1. #1
    Join Date
    Aug 2008
    Location
    Austin,TX
    Posts
    2

    Got a mismatch, now what?

    Was doing a google search and found your forum.
    Our maintenance crew was going through a building that we just recently took ownership of and cleaning it up before allowing rentals. One of my guys noticed we have an 3.5 ton Rheem AHU that is marked 4 years old, matched up with a new(hand written start up date of March 2008) 3.5 ton Haier condensing unit. We noticed the suction pressures running a little high, but the discharge pressures seem normal(80/225 on a 95deg day w/80deg space temp). The unit ran all day long and wouldn't get below 78deg space temp. I though maybe we might have air in the system, so we changed out the liquid line drier and pulled a good vacuum; that didn't change anything. I am assuming the AHU isn't a 13 seer and that the new condensing unit is a 13 seer minimum. Looking for answer to a problem none of us have experienced before.

    Thanks in advance

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,064
    The mixmatch could be the sause, so could several other things.

    Did your guys take any readings.
    SH, SC.
    Entering WB and DB, leavin DB.
    Air flow in CFM.

    Your vapor pressure indicates a high indoor load. Your head pressure indicates little to no ID load.

    So your pressures are not normal.

    Are you sure then condenser isn't an R410A condenser on an R22 evap coil.
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  3. #3
    Join Date
    Aug 2008
    Location
    Austin,TX
    Posts
    2
    After I went out to the job, found out we have a 4 ton horizonal coil w/TXV matched up with a 3.5 ton condensing unit. Outside temp was a little cooler today, 91deg before the condensing coil and 103deg leaving; 12 deg difference. We had a 20deg diffenence across the evap coil, 52 supply and 72deg return(which is located up on the ceiling with a new pleated filter), with a tstat reading of 75deg space temp at about 60inches. Unit was running for 3 hours and only dropped the temp on the thermostat 2deg. Found a decent air leak on the bottom side of the leaving air transition that was attached to the evaporator coil box; we taped and sealed that up. Just doesn't seem to be able to drop the temp with an empty house. I can just imagine renting guest going in and out the doors and with room for probably about 30-35 people in an 1860 sq foot building, that isn't going to keep up with this Texas heat. I'll have the guys give me the readings your asking for before they come in at the end of the day; got your message after I was already back out in the field yesterday.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,064
    Is this a banque room/hall?

    Does it have a fresh air intake?
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    How many times must one fix something before it is fixed?

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