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  1. #1
    Join Date
    Mar 2007
    Location
    MD, USA
    Posts
    47

    pressure limiting txv's

    problem on a walkin freezer today. running warm about 40f. 360psi head 15 psi suction. R-404a. No reciever TXV system.
    Between top of box and cieling approx 2 and a half foot. with both walkings next to eachother in maybe 12ft from wall to wall walking in cooler walk through to freezer. Both boxes are packeged condenser and evaporator on top of the box. return and supply next to eachother in ceiling of box. No sight glass on system but an alco pressure limiting TXV no CRO valve, electric defrost.
    Feel discharge line very very hot with a very warm liquid line, quickly rinse of condenser (construction dust), head pressure comes down slightly but still hot. all fans running condenser and evaporator, notice ice build up at inlet of evaporator hose out evaporator, remove ice.

    little temp drop across filter drier decide to add a little gas just in case its low on gas but because of dirty condenser and recirculating air raising head. No increase in suction and coil is still not flooding out.
    Decide to install a new TXV external equalized with a KT-43-RZP head, filter drier 0163s, and a sight glass. Vacuum down and leak check. GOOD.

    So i weigh in a charge but adjust so my sight glass just clears itself. box is starting to drop but still not flooding out coil completely. Even with ZP charge head im reading suction 30 psi approx -5f with about the same head pressure as before. Suction pressure does start to drop but have to leave. Box was at 20f when i left with the coil still not flooding.
    My boss told me to tell them to check on it in the morning to see if it came down all the way. I left there about 4 ish, so let it run through the night.
    Sorry no mod or serial numbers.(meant to get but had to run).

    Really hoping I have not missed anything pressure limiting TXV's have blowen my mind today. Will the box take its time coming down to temp because of ZP head. Any ideas. THanks
    If you can't be goodlooking at least be handy

  2. #2
    Join Date
    Aug 2006
    Location
    st.petersburg,fl
    Posts
    803

    Lightbulb

    MOP of that power head is 45 psi
    Also that powerhead is for a 502 system not a 404
    The powerhead you want is a kt-43-szp
    Isn't sanity just a one-trick pony anyway? I mean, all you get is that one trick, rational thinking, but when you're good and crazy, well, the sky's the limit!

  3. #3
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,312
    You didn't give any model numbers but that unit sounds like it may be a Heatcraft Pro3 package. Here's their I&O manual:

    http://www.heatcraftrpd.com/resource...l/H-IM-82A.pdf

    Since there's no receiver the system is critically charged. If the condenser is clean, has good airflow and is not in a high ambient area, the high discharge pressure would normally be due to a refrigerant overcharge. But if this were the case I would expect to see high suction as well...but you don't have that.

    I suspect if you first check the liquid subcooling leaving the condenser at the conditions you described, you will find it to be excessive. High subcooling and a high TD would indicate that the refrigerant is stacking up in the condenser thus robbing you of effective condensing surface...giving the appearance of an undersized condenser.

    Now on the low side, if the TEV is correctly sized, there's adequate subcooling at the valve, the charge is correct and you have high evaporator superheat (which I also suspect), there has to be a reason why you have a starved evap. You've changed the TEV, so assuming that's OK, check the evaporator coil for even distribution across the coil. A blocked distributor or two would cause the low suction due to a starved evaporator and could also be the reason for the stacking of refrigerant in the condenser....ie, most of the refrigerant is trapped at the other end of the system. There may be other causes here. Even a plugged equalizer line could be the culprit, but as I see it there has to be some form of low side restriction somewhere.

    As for the TEV with the MOP thermostatic element, I don't see that this has any bearing on your problem. At 15# suction, you're well below the nominal range of the MOP of 35# (not 45#) so the MOP is out of the picture.

  4. #4
    Join Date
    Mar 2007
    Location
    MD, USA
    Posts
    47
    yes sorry i meant to write szp, thanks for the info. No call back today which is good cos owner seemed to be all over it, so im very sure if it wasn't at temp he would have called. Probably gonna find out on the first hot day we get this year. I tried to make sure i didnt over charge it got a clear sight glass then left it. So i think that we shall see thanks for the info yet again
    If you can't be goodlooking at least be handy

  5. #5
    Join Date
    Jan 2007
    Location
    maine
    Posts
    788
    i sight glass is useless in a system with out a reciever beside being a moister indicator and another chance for a leak

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