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txv on dry charge condensers

when putting in dry chge 13 seer condensers on 10 seer evaporator coils would it be better with a txv. if so can you get one that will fit on all different brand coils rather than try and find one for each unit ?.i do try to get people to go to 410a units but sometimes they don't want to tear out all of the equipment and spend more money. i have put in several without any problems,even some still have orifices and work good.a couple of the first ones i did ,they have txv on them because they were same brand as new condensing unit and were easy to get.i know alot of techs. don't like this option and say it doesn't work well and some say its ok. i personally haven't had issues, and years ago we were putting 10 seer into 8 seer coils and didn't think twice about it. i know this isn't best option for a number of reasons but the reality is that someone will get the work if you don't give option. i tell customers about efficiency issues and give them options and do suggest matching up is best.there seems to be a real mixed opinion subject for sure and continues to be this way still.i am not talking about real old stuff, i am only talking about 10 to 12 years or less on the evap. coil and no leaks etc.several wholesalers that sell them say there is no problems with or without txv installed and they have to process any warranty with condenser unit. i also have not seen any thing as of yet in writing that says about voiding warranty from manufacture as of yet about match ups. wow very confusing and just wanted to see what ideas and or experiences other guys had on this forum...

Comments

  • TechmanTechman Posts: 2,144Member
    edited August 2012
    Dry charge

    I have replaced my share of 10-12seer cond unit w/ a dry charge 13seer cond unit.In some I have left the orifice/piston in place  and in others I installed a TXV. NOT ONE of those systems operated "properly" according to my gauges and thermometers for subcooling and superheat.Most of these converted systems operated  close to normal ,close enough that the homeowner was just as comfortable w/ the new cond unit.The major factor is the 13seer unit hiside press.It is LOW, to low to have the proper pressure drop across the metering device. On a couple of Rheem/Ruud 13seer units I replaced the new 3 wing cond fan blade w/ the older typical 2 wing  R/R fan blade that they use. The head came up and so did the low loside press. Both TXV and orifice work better w/ a proper press drop .
  • Paul_69Paul_69 Posts: 247Member
    dry charge

    thx for your insight techman. i have noticed the same things with pressures and superheat and subcooling.i was putting in charge in and removing trying to set it right. i would finally get decent superheat and 17 to 20 degree drop on evaporator and was removing moisture and working good that way. but i am really wondering about these even though i put in 7 or 8 units.are you better off not doing this and just upgrading the whole system?when they have some age on them its easier to say hey you need new cond., coil, lineset etc. but when the evaporator or air handler is perfectly good and not old it gets more difficult to say everything has to be replaced. someone will change just the condenser if you don't give option. i am not saying i want to do the wrong move just to get the job . i am just throwing this out there as this is very confusing and alot of mixed opinions, you know what i mean.i just want to get educated with this stuff and move on.
  • Paul_69Paul_69 Posts: 247Member
    low head

    techman i was wondering about what you said about lower head pressure on 13 seer condensers. why would that be a difference on pressure drop on metering device?would the evaporator coil being 13 seer cgange that low pressure? are not the metering devices the same? thx
  • TechmanTechman Posts: 2,144Member
    edited August 2012
    Dry cond

    Along the lines of a capillary tube metering device and/or an oil nozzle and/or a piston orifice. Also along the lines of a TXV, a 25t  r-22 TXV w/ a 40 lb.press drop across the TXV will give only 21t or so and the same  25t TXV w/ a 200lb. press drop will give  a whopping 34.9 tons of cooling .Its called "extended capacity charts" and it does make a difference.So the 13seer has more cond coil heat rejection surface than a 10seer so the head press is lower ,saving energy.Except ,the metering device needs that higher press drop to produce the needed freon flow to give us the proper low side press. Normally on a 72* day w/ a hi side of 175-185 and a loside of 60-58 that is only 110-115 psi press drop and on a 95* day the head is 275 or so and the loside is about 65-70psi and that is about a 200psi drop.But w/ a 13seercond w/ a 10-12seer evap the high side press will be about 250-230psi or so on a 95*ambient which is not enough press drop to have the metering device work properly.  On an 80* ambient day or so w/ a 13seer to 10seer combo the loside press is close to freezing (57.8psig) and on a 75* ambient the loside press is freezing.KindaSorta!
  • Paul_69Paul_69 Posts: 247Member
    so

    then a txv doent matter either. should we be putting these 13 seer units in 10 seer coils then at all?do you still install them? it sounds like it isn't worth it regardless. of the age if this stuff is going to happen. like i said i put a few in but wasn't happy with readings but i also haven't had any call backs for freezing coils or cooling complaints.wow this is confusing to say the least.  thx for replys
  • TechmanTechman Posts: 2,144Member
    edited August 2012
    Dry Units

    Anytime you mix/match different seer's you get different results .But it sure seems to show itself more w/ the 13seer cond  to 10seer evap.Knowing that the press will not be normal and living w/ the results as long as the customer is properly comfortable is what we want. I 've heard many horror stories from tech's(usually at the supply houses) about the H.O. complaining and complaining.I seem to have very little trouble.Not that my conversions are trouble free as compared to say ,your conversion  , but I've spent LOTS of time "playing"w/ my system's to get it running "good" . I have also changed cond fan blades w/ a different pitch for less cfm's.Yea it may be confusing at first but so was this entire profession confusing @ first also. Look at it as a challenge and how are you going to stand out from the crowd.Lastly, it comes down to the customer NOT picking up the phone because they are satisfied.One more lastly, if the H.O. says they can only afford a cond unit then thats the way it is. I am not selling something that will not work ,I am selling something that will work, just differently.
  • John Mills_5John Mills_5 Posts: 935Member
    mismatch

    Our biggest issue was a dry unit on a 28 year old air handler. That poor unit had to be so overcharged to get the suction above freezing I guarantee that little scroll won't last. At some point it's time to say no to such a mismatch.



    The rest of our dry units have been on evaps at least meant for a 10 SEER and have been reasonably close in getting the numbers to line up. Still hate doing it but if we don't, someone will. Won't do it on a HP, that's just asking for a nightmare.
  • Paul_69Paul_69 Posts: 247Member
    mismatch

    thx for replys, john, techman. i think this topic could go on forever. i think if i put any more 13 seer into 10 seer units i would add txv and inform customer in writing the consequences involved and if doesn't perform well or up to their expectations that a new coil upgrade to 13 seer would be on them and tell them they really should considering whole 410a upgrade first. also any service calls to adjust would not be covered underwarrantee as we don't know what will go on with mismatch. now granted i have been lucky i have replaced about 8 to 10 condensers in last 2 years and have not had a issue with operation and even have gone back for annual tune ups and no problems. but on the other hand i have read and heard alot of horror story's that make me want to walk away if they don't want whole system rather than make a sale and let someone else do it.i am really mixed up for sure. i only have been doing them on 12 year old or less. any input would be appreciated!!! thx
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