txv problem????????

[hvac17011]

took on this account did pm now starting repairs.units have not been looked at in 5 yrs. up to 7 compressors numerous units flat.anyhow.This is trane rtu the style has 3 cond fans spash coil in supply air stream. repaired leak on condensor coil,replaced drier pulled vaccum to 400 microns.weighed in factory charge.this has two tin cans.the one compressor is out so im trying to charge this with just the one circuit running.Heres what I have245# discharge 55-57 suction 32 deg subcooling 25 deg superheat(is swinging a bit)17 deg split.coils were just cleaned filters ok belts ok. I am guessing problem with txv although I took bulb off and put in hand suction pressure did go up a bit to 65#.

[rob10]

1. Its overcharged. Subcooling should be around 13 degrees.

2. Locate the txv buld on a horizontal run just leaving the evaporator at the 10 or 2 o'clock position. Check the airflow, adjust the txv to the proper superheat.

[Edited by rob10 on 06-29-2004 at 08:38 PM]

[lwarren]

Even know you have fair suction you could be overcharged and have a restriction.

[seaboard]

I would like to know what the return and supply temperatures were as well as outdoor ambient. It definately sounds like you have liquid stacked in the condenser and you most likely have a defective TXV powerhead. I wouldn't go further with it until the other compressor was installed and you have the system totally up. I have seen the units you are describing (SACA's) with a subcooling circuit in which the liquid lines go through a cap on an extension of the condensate drain and give the unit additional subcooling. If you have this and are in a humid climate this can run up your subcooling. High superheat when a unit has just been started and return air temps are extremely high is not unusual and should be expected. Conversely, if you put a compressor in a unit on a hot afternoon and have a return air temp of 85 degrees from a hot return plenum but your superheat is 12 degrees, you may flood the next morning when the return air temp is lower. Maybe not, it will depend upon the range the valve has. While TXV's react to the suction line temp, the pressure differential does matter as with other metering devices. Generally speaking, the larger the valve, the more this is true.

[airworx]

32 degrees subcooling means your way overcharged.
should be around 10 degrees. also if you had a bad powerhead you would not have 50 lb suction pressure.
suction is low because txv is pinched off

[hvac17011]

I dont know I weighed in factory charge

[bjefferson]

That much subcooling means either overcharged or a liquid line restriction.The restriction should be obvious.There should be a frost line.could be junk in the txv.I would try to adjust the txv if its adjustable.

[hvac17011]

I weighed in charge. Another tech was hooking up thermometer and I had 18 deg subcooling and I wasnt even close to having factory charge so I guess thats why im leaning towards restriction. I replaced drier so thats ok. I have heard this argument before but what will I see if I have crap in inlet screen to txv.liquid will back up so will I have high subcooling and suction will be lower.If im totaly off base.let me know im still learning.I had a larger unit the other day that you could actually feel tempdifference on liquid drier and thats kinda how that was acting high subcooling high superheat low suction pressure. I havent been back on that (they wanted quote)

[chiller32]

this rtu is it an Intellipak? with scroll comp?

[hvac17011]

its an older trane It has three condensor fans. coil slants and filter driers are outside unit under coil.It has a splash coil on supply side of evap coil.I dont think they are scrolls

[Dad]

It maybe a BYC130G3L0DA. Had one last week doing similar, but many leaks on the old evap coil. Customer didn't want fixed. New one on the way.

I bet our resident Trane Guru will know. "txtraneman" where are ya?

[hvac17011]

ill get model and serial that looks familiar

[airworx]

your not restricted, if you had a dead powerhead or stuck valve or trash ie restriction then you would not have 17 degreesplit and probably not 57 lb suction pressure.

[nexmech]

As said earlier it looks like you just need to adjust your txv on the system. If you had a restriction your head pressure would be high also. Another thing where did you take your condensing pressure at the compressor? If you didn't take it at the liquid line then you didn't offset for the pressure drop across your condensor so your subcooling may not be that high. It is usually about 6 psi across newer units but if this is a older unit you will probably want to add a few more psi. The only way to tell for sure is to put in a tap at the liquid line. txtraneman will probably have the answer for you whenever he reads your post but i just wanted to add my two cents

[twcpipes]

partial post:

>>>>I have heard this argument before but what will I see if I have crap in inlet screen to txv.liquid will back up so will I have high subcooling and suction will be lower.<<<

Yes the liquid will back up. Also, Unless they have changed TXV designs with the new miilenium, the powerhead "opens" the valve. If you have a flat charge in the bulb/powerhead the valve will go to a minimum closed. BUT, if the valve has lost only part of its charge, it will partially close as it is dictating a lower temperature that it really is as long as there is one tiny molecule of liquid.
With all these questions arising may I offer a suggestion:
get a free Sporlan catalog. There is a wealth of information in them besides just showing products. You can also call your local Sporlan Rep directly and he/she will answer any and all questions. If you get a catalog, and have questions, call them with those also. Alco will do the same. At least they have for the last 40 years I have picked their brains. In my area, they bend over backwards to help field people.
Good luck,
tom

[hvac17011]

I have done repairs on 3 of these units this week. The first one as discussed in this post and 2 others. The other two I watched the charge alot closer and installed sight glasses. The first one is several onces below factory charge as on nameplate14# 6 oz. The other two I stopped around 12#.sight glass clear 15 deg subcooling superheat 16.225 hp 64sp.so go figure. But im still having a hard time deciding if I have a restriction on overcharge.I have some other units that look similar high subcooling low suction. If airflow is ok I always thought if you were overcharged suction would be high so in this senerio looks like a restriciton bot i have gotten differing opinions.nerver stop learning.

[hvac17011]

also these txvs are not adjustable

[twcpipes]

If I may also ask:

1. What is the tonnage on the valve vs. the unit capacity?
2. Are the valves uni-body or are you lucky ehough to have valves that the powerhead unscrews as well as a nut at the bottom you could add a stem like maybe a Sporlan?
3. If your at a point where you feel you have to change the valve can you put a schraeder at the liquid line inlet to the TXV?
4. Has the compressor been changed in this unit also?

You mentioned the suction went from 58 to 65psig when you held the bulb in your hand. It does sound like a partially blocked inlet screen though even at that especially if there was no noticable drop in refrigerant temperature.
You gotta love these jobs that should be straight forward and turn to doo-doo. LOL
Thanks, tom

[hvac17011]

original compressor does have chageable powerhead

[bjefferson]

Like I said before.Too much sub-cooling is either an over charge or a restriction somewhere in the liquid line.You see frost where the restriction is.If its just a partial restriction you may only see sweat on the line.But the temperature difference will be obvious.

[air1]

You have a bad TXV. Replace the powerhead or the complete TXV assembly.

[beercat33]

Ok,,,, since we're talking about the old trane units with splash coil...(now i know what that lil coil is for) I was working on one today, and noticed an oily spot on the far end of the evap coil. It does show low pressures and i'm pretty sure it's a small leak. I'm wondering if there is an easy way to pull that coil out so i can repair the far end. It's about a 7 ton unit with only one compressor. any secrets ?

[Dad]

Beercat...

There is no easy way. If you pull it, replace it. Cheaper in the long run. Yes I know the coil very expensive but it will leak again and again.

There are 102 (give or take a few) joints on the end of the coil that you can get to. The rear of the coil has about as many. If the front of the evap coil has less than 6 or 7 leaks you can fix them with 45%. Been there, done that, have made customer happy. You can't guarantee this work or the possible back side leaks, it is only a band-aide until they are ready to replace the coil or replace the unit.

Average invoice to fix without guarantee runs around 10% of the cost of a new unit. You can replace with a new Trane for what the replacement evaporator coil and labor will be. (+ -)

[seaboard]

Originally posted by hvac17011
I have done repairs on 3 of these units this week. The first one as discussed in this post and 2 others. The other two I watched the charge alot closer and installed sight glasses. The first one is several onces below factory charge as on nameplate14# 6 oz. The other two I stopped around 12#.sight glass clear 15 deg subcooling superheat 16.225 hp 64sp.so go figure. But im still having a hard time deciding if I have a restriction on overcharge.I have some other units that look similar high subcooling low suction. If airflow is ok I always thought if you were overcharged suction would be high so in this senerio looks like a restriciton bot i have gotten differing opinions.nerver stop learning.

I still think you have a weak powerhead on your TXV. The only thing that I found odd about your first post was the split you said you had. With only one compressor operating you said you had 17 degrees. Perhaps you were reading the temperature to close to the coil. It's tempting on these units to simply drill a hole in the middle panel directly after the splash coil but you will get a false temperature reading there. If you have a TXV on a unit and the subcooling is high, that does not necessarily mean that the unit is overcharged! I think your question is whether when liquid starts stacking, the valve will throttle back causing your suction to drop. It will not. The valve is simply trying to keep the suction line at the temp it is set at. As the line warms it opens, as it cools it closes. Adding additional refrigerant to a unit will stack the coil and eventually the pressure must climb as you run out of room in the condenser. At this point the pressure differential at the valve will be higher and then the valve will throttle back to keep the system from flooding. In your case you have a low suction pressure with a higher than normal superheat and high subcooling. Your valve is non adjustable so replace the powerhead or the valve. Often you will know when you replace the powerhead whether it's going to do the trick or not. If you unthread it and the pins aren't touching the disc and offering resistance but you thread the new one on and the disc immediately touches the pins and depresses opening the valve you can be pretty sure the powerhead is going to do the trick. Also, check your scale and if it's a TIF throw it off the roof and turn it in for tool replacement and get a CPS.