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  1. #1

    trane by the book, and TEV test procedure?

    Thanks again to Jayguy for the manual for a Trane CGAC chiller.

    While it was hard to come by, it was worth the wait. I have to say that the manual has one of the clearest presentations of the theory of ops for any owner/operator manual I've seen.

    Excellent piece of work.

    I continue apace with my plan to replace a bad compressor with an equivalent scroll and I'm wondering if there is enough internal volume difference in the compressor designs to make much difference in the target charge.

    also, i have a suspicion regarding the thermostatic expansion valve being blocked or inaccurate on the other circuit -- although i am thinking that a stuck compressor valve might give similar symptom.

    The manual calls for testing the TEV in the event of the exhibited symptoms (low discharge and suction pressures. While my first instinct was a minor leak and low charge, I'm getting no bump on the discharge out of the compressor so the system is blocked somewhere. I'm more suspicious of the compressor itself ,but the manual (and despite all the good things I said about it) doesn't suggest any method for testing TEV. I can figure out if its blocked but I'm not sure how to test its range of response to various superheat readings.

    Thanks

  2. #2
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    post your pressures and temps and amps and...etc.

    as far as testing a txv, remove the bulb and put it in your hand to warm it up...NO hot water or torch or anything like that. then put it in ice water...those are basically the two extreme conditions for a typical a/c unit.

    good luck.
    When the rich wage war, it's the poor who die - Linken Park

  3. #3

    pressure, temperature, amps

    got back there today,

    ambient temps 82.6 standing pressure equalized at 115 high and low

    energized the crankcase heaters for a couple hours. pressure went up to 122

    started the unit, got a brief spike in temp and pressure on the high side
    up to 165 psi.

    low side dropped down to 10" vacuum and high side stabilized around 150psi.

    temps on the liquid line just before the dryer and TEV 78.7 and on the suction line exiting evaporator 80.2

    I forgot to take the water temp of the building water circulating through the evaporator (damn) but I doubt it was much different than ambient.

    the motor was reading about 6 amps per leg and it's rated rla is 23.6 amps.

    In any event the numbers were so far off and the system so slow to equalize -- took a day the last time I ran it -- I figure there has to be a blockage, either the dryer or TEV.

    brian

  4. #4
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    4,396
    it is possible that your txv has debris in it but my guess is that the txv power head has lost its charge. look (feel) for a crack or break in the cap tube from the bulb to the power head. if you find one, you may be able to just replace the power head depending on the brand and model of the txv. or you may have to just replace the whole txv.

    good luck.
    When the rich wage war, it's the poor who die - Linken Park

  5. #5

    TEV adjustment after replacement

    Jayguy,

    I believe I bought the identical valve although the numbers are long gone and hard to find. In theory I could pull the head and thread the new one in which might be handy in terms of not cutting off any more of the relatively short 7/8" lead coming from the evaporator. (I'm convinced this thing is going to be running for years so I'm trying to save some brazing space for later).

    one way or another the drier is of course being replaced and the site glass is none too pretty although I can still see through the glass but before it rusts out and loses seal thats going.

    so anyhow, there is almost enough room with a short screwdriver to adjust the TEV. I was figuring on maybe using a readily available P/T chart for r-22 and trane specifies in the manual a range of 10 to 15 deg. superheat. however all the 'calculators', i.e. tables and slide charts and so forth add weetbulb evap. and dry bulb cond. temps to the calculation.

    Of course this is a chiller so there is no air flow over the evaporator so I'm thinking supply water temp would be the wet bulb temp or???? or should I estimate the interior temp being applied to the water and it's humidity??? Also notice that all the fieldpiece attachments that calculate superheat don't seem to have those comparative metrics or should I say psychrometrics ( I can't spell it, I just copied from another thread).

    Rather it just takes the pressure and temp at the evap exit. Is this adequate from the point of view of the unit itself. Any advice on how much adjustment, i.e. how many turns or fraction of a turn to apply at a time to an Alco valve when trying to hone in the superheat to the required 10 to 15 deg.

    thanks,

    brian

  6. #6
    Join Date
    May 2008
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    Jax Fl.
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    Usually the problem is with a "flat" powerhead on the TXV. When you change it, be sure and cover the entire top of the powerhead with RTV/Silicone to prevent corrosion failures.

  7. #7

    tev failure

    Quote Originally Posted by JRINJAX View Post
    Usually the problem is with a "flat" powerhead on the TXV. When you change it, be sure and cover the entire top of the powerhead with RTV/Silicone to prevent corrosion failures.
    with you there. when i looked at it i noticed corrosion all around the exit of the capillary from the flatpower head as well as around the edges. nothing like rtv. when they outlaw that i'm out of the business.

    still wondering if I can just adjust the TEV using P/T chart or if it is more highly appropriate to factor the loads, i.e. condensor ambient and evaporator load, here it is water chiller and not air so do I just use water temp? The fieldpiece superheat subcooling heads only take pressure and temp although you can get a smart handle that will allow you to change heads and add wet bulb evap and dry bulb condensor readings, but I'm thinking that is cool but maybe overkill.

    brian

  8. #8
    Join Date
    May 2008
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    Jax Fl.
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    Assuming the chiller still has the OEM expansion device, that won't have any minimum load issues, setting the TXV's spring pressure using superheat is OK. If you can, test each circuit's superheat with min/full load. You might want to log the chiller against the original T&B/startup sheets to see if any changes have occured over time. This might also be a good time to test Glycol/water treatment.

  9. #9
    Join Date
    Sep 2007
    Location
    Texas
    Posts
    3
    You can always unscrew the power head and put in a penny or a dime and screw it back on. If the problem goes away, you know it's the powerhead.

  10. #10

    update, adjustment?

    OK, it was the TEV. It is a Sporlan with a replaceable head. So the frig store didn't have the vxp100 head most suited to chiller application but they had a vga head for general air conditioning service that operates in more or less the same temp. range. This circuit has never been serviced so it had the factory charge in it. I took that out, changed the head, and put it back.

    Now we stabilize at:

    48 psi at the evap exit
    180 psi head.
    Suction line temp is 27.2

    Obviously that is giving me some frost back to the compressor at standard water temps, i.e. about 50 in and 42 out. So, for the time being, I raised the water temp setting so I'm running more like 58 in and 50 out and that cut the frost back down, but I'm guessing I ought to adjust the TEV so I can return to summertime operating temperatures.

    I'm assuming that maybe the slightly different temp range of the head is giving slight different result -- given the scale tells me I put virtually identical charge back in as I took out and this circuit was running fine before the TEV total failure.

    Another mystery here is that Trane used a 5 ton valve on this 7.5 ton system. No combination of evaporator delta T and operating target temp and head pressure shows any of sporlan's 5 ton valves as adequate for 7.5 tons ( although at higher pressures the specs do just cross 7 tons. The valve has worked fine for years so I think I'm just going to go about adjusting it and see if I can close in on desirable suction temp and superheat. But, anyway, there is an Alco without a replaceable head that was installed on the burned out half of this unit and I have in mind to replace it with a more original TEV while I've got that circuit broken down.

    I'm going to go with an SVE 5 which is, according to sporlan, the most analogous aftermarket product to the OEM XVE 5 that was orginally employed by Trane. But I'm wondering what the design benefits might be of using a valve at the low end of the size continuum suitable for this job. I'm thinking it actually would improve the subtlety of adjustment since each bit of travel in and out of a smaller orifice is going to be smaller adjustment. And sporlan does have changeable orifices so if for any reason its not right in some way, I would be able to upsize after the fact without unsoldering.

    Just looking to hear what thoughts anyone has beyond the sporlan tables about picking TEV sizes. Is there an advantage to staying as small as possible?

    thanks,

    brian

  11. #11
    Join Date
    Apr 2002
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    Dallas, TX
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    Quote Originally Posted by archibaldtuttle View Post
    Now we stabilize at:

    48 psi at the evap exit
    180 psi head.
    Suction line temp is 27.2
    Low load.

    Quote Originally Posted by archibaldtuttle View Post
    I raised the water temp setting so I'm running more like 58 in and 50 out and that cut the frost back down, but I'm guessing I ought to adjust the TEV so I can return to summertime operating temperatures.
    You should first simulate design conditions and verify TEV operation at this condition before making adjustments. Then look at your minimum load conditions to see how well the TEV is performing.

    Quote Originally Posted by archibaldtuttle View Post
    Another mystery here is that Trane used a 5 ton valve on this 7.5 ton system. No combination of evaporator delta T and operating target temp and head pressure shows any of sporlan's 5 ton valves as adequate for 7.5 tons ( although at higher pressures the specs do just cross 7 tons. The valve has worked fine for years so I think I'm just going to go about adjusting it and see if I can close in on desirable suction temp and superheat.
    I'd give the OEM the benefit of the doubt here.

    Quote Originally Posted by archibaldtuttle View Post
    I'm going to go with an SVE 5 which is, according to sporlan, the most analogous aftermarket product to the OEM XVE 5 that was orginally employed by Trane. But I'm wondering what the design benefits might be of using a valve at the low end of the size continuum suitable for this job
    The SVE-5 is an almost perfect replacement for the XVE-5. Trust me.

  12. #12

    nail on head

    Quote Originally Posted by Andy Schoen View Post
    Low load.
    That is for sure. 80% of the fan-coils were turned off although I have long since discontinued all the zone valves in the units so I was getting circulation throughout the building and through the chiller.

    The staging thermostat isn't too highly sophisticated of a unit and I was mostly watching the superheat and subcooling temps, I simply assumed if the load was low it would make temp in a hurry and then shut off, but probably the delta "T" dropped down on inlet temp before I got to the shutoff temp on the outlet.

    I should have kept another couple of monitors on the inlet and outlet water throughout. I've got one of those two temp fieldpiece heads and another handle, but I have to make up a couple more k style clamp on thermisters that will grab the 2" pipe. Off to the workshop.

    No adjustments till I try that out.

    But this brings up one of my pet peeves. I would like a more sophisticated staging and water temp controller that could monitor delta T and or rate of drop and outdoor temp and give me more efficiency and unit protection by raising chiller target temp as outdoor temp falls. These intelligent controls are pretty effectively worked out for heating but I don't seem to find them on the cooling side. The same general approach could be adaptable to split systems, chillers, evaporative home cooling in desert southwest, etc. so I would think the market would be sizeable. It could be more complicated if the control factored in humidity as well, but it still is pretty simply silicone engineering. Am I looking in the wrong places, do these controllers exist already or should I go off and invent one.

    Brian

  13. #13
    Join Date
    May 2008
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    Jax Fl.
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    I am going to suggest two possibilities; The chiller bundle is full of "Mud" at the bottom [covering the lower tubes], or the "pass" gaskets could be leaking by and short circuiting the refrigerant flow through the barrel.
    This will result in low Delta and low saturated suction temp, like yours appears to have.

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