I would say a combination of low charge and restricted metering device.
on tranes the drier is inside the unit

 

With such high superheat and normal subcooling, I would be willing to bet that TXV is malfunctioning and it's undercharged by 1-2 pounds. Sensing bulb could be low on charge or something fouled up the needle. Fortunately, that's probably a bolt on TXV so it's real easy to change out.

 

The SC might be normal , but the normal head for a r410 system w/ a 68* ambient should be closer to 300psi and the normal suction press should be closer to 110psi w/70* IDB. Those p/t's sound more like r22.

 

As others have said it sounds like a TXV and maybe low on juice. Check the serial number, it may need the snake oil to clean the goo out of the TXV.

 

But if the system was low on refrigerant wouldn't that show a low head pressure and suction as well? Right off the bat I would have a high superheat and low subcooling, no?

By seeing that it had 8 degrees subcooling would mean that the condenser has the refrigerant it needs to operate at design subcool specs with the threshold of +/- 3 degrees. Unless I'm not reading the data plate right isn't that what it means?

I don't want to sound like I know the game and that I'm better because I'm not but looking back on what I learned in school as a reference seems to conflict. Then again theory and reality are opposites most of the time.

The serial started with a 14 and I remember something trane made that did in fact clog up the TXV and yes some oil had to be put in to dissolve it. Our company has been going around and applying the oil to those with such serial numbers that were infected.

 

You are showing low head.

Look at it this way. If everything is working properly you would have 8°-12° SC and 10°-20° SH.

So lets look at just the SH side first. What causes high SH, low on charge or a restriction. 8° SC would discount the low on refrigerant right. That leaves a restriction.

If you have a correct charge and a restriction you would have higher SC right. Since you have normal SC and a restriction you must be short on charge.

Does this explain better or is there other info I should consider?

 

With a normally operating TXV on an undercharged system, you'll find that SH may be normal with some subcooling. Not until you reach 0-3 degrees SC will your SH start to increase.

See, as the system loses refrigerant, the TXV will open more and more to keep the SH normal (10 degrees), so there's always a column of liquid before the TXV. When it's fully open and still not enough refrigerant is in the evaporator, then your SH starts to rise.

In your case, you have an almost normal column of liquid behind the TXV, but it's closing down way more than necessary. There's no reason to have 50 degrees SH if you have 8 degrees SC other than a restriction (TXV being the restriction). It's also undercharged because if it were charged fully, your SC would be well above normal (15-30 degrees).

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Only ways your liquid line can be colder than the ambient is if there's a restricting before the pressure port or the condensing coil is wet.

 

But it's not!
68 deg ambient/liquid line saturation 71.4 deg........ close, but not....

With a normally operating TXV on an undercharged system, you'll find that SH may be normal with some subcooling. Not until you reach 0-3 degrees SC will your SH start to increase.

See, as the system loses refrigerant, the TXV will open more and more to keep the SH normal (10 degrees), so there's always a column of liquid before the TXV. When it's fully open and still not enough refrigerant is in the evaporator, then your SH starts to rise.

In your case, you have an almost normal column of liquid behind the TXV, but it's closing down way more than necessary. There's no reason to have 50 degrees SH if you have 8 degrees SC other than a restriction (TXV being the restriction). It's also undercharged because if it were charged fully, your SC would be well above normal (15-30 degrees).

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To the op, correct answer was given above with txv malfunction on top of low charge!

 

Bad TXV. Not necessarily low on charge. Many times I've had normal subcooling and a ll restriction. The subcooling skyrockets when some knucklehead jams a bunch of refrigerant in it to get the suction pressure above freezing.

If it's a copeland compressor from 2014 I can almost guarantee the TXV needs some of the magic miracle additive ac renew

 

Bad TXV I get but someone please tell more about a low charge on top of that?

 

I don't think it's low on charge

 

How can the SC be perfect and be used as a "cornerstone" for a good running system when the lo side is lo and the hi side is also lo?

A good running system has a good suction press, a good hi side press, a good SH and a good SC.

 

At start up you'll likely have high head for a while until you get a large column of liquid built up. With a real good restriction you are cooling more than you are pumping and the pressures get close to ambient saturation points when the start to happen subcooling goes down..... Much like checking subcooling in say fifty or below outdoor temps. You would think it would subcool real good yet remains around 4 or 5 degrees

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Correct me if I'm wrong, but if I close my txv(restrict), subcool increases (as in refrigeration, close your valve and sight glass clears)

 

Or high subcool with restricted captube.
Restriction causes liquid to stack in condenser, so if txv is restricted, he would have higher subcooling than under normal operation....... thus low charge

 

Okay, so with what you guys are saying is making sense. The more I think about the clearer it becomes. But I am still lost. I feel like I need a refresher course with refrigeration..

 

It comes with practice, you'll get it eventually. Let's start with a normally operating system with a TXV. What do you expect to see? 10 degrees SH and 10 degrees SC (assuming SC target is 10 degrees). What does that mean? It means that the TXV is throttling the right amount of refrigerant into the evaporator coil to absorb the right amount of heat from air passing over it. If we increase the amount of heat for that evaporator to absorb, our SH will climb, so the TXV will open more to compensate. If we decrease the amount of heat for the evaporator to absorb, our SH will drop, so the TXV will close more to compensate.

What if we were undercharged? Let's say we have 10 degrees SH and 5 degrees SC. Even though we lost refrigerant, the TXV can maintain normal SH because there's still a column of liquid behind it, but if we add more heat to the evaporator, the TXV is going to open more and there might be a point where it's fully open and can't maintain SH because there's simply not enough refrigerant to meet demand. Our head pressure/saturation temperature will driven be closer to the LL temperature.

What if we were overcharged? Let's say we have 10 degrees SH and 18 degrees SC. Again, the TXV maintains normal SH despite the heavy amount of refrigerant behind it. But if we continue to add refrigerant, it will keep stacking up behind the TXV, so our SC increases more and more. Our head pressure/saturation temperature will be driven further away from the LL temperature.

What if we have a restriction? It depends on where the restriction is, but it's most often at the metering device. So let's say we're seeing 35 degrees SH and 15 degrees SC. This tells us the TXV is closing down when it shouldn't because there's a good column of liquid behind the TXV, more than normal, but it's not maintaining 10 degrees SH.

What if we have a restriction and we're undercharged? We know in an undercharged scenario, our SH will be high, but our SC will be low and most often 0. So if we see our SH is high and SC is slightly low, that gives a good indication that not only is the TXV not doing it's job, but there's not enough refrigerant in the system either.

 

I just looked back on my notes,

Low side pressure: 65 PSI (10*F)
High side pressure: 210 PSI (72*F)
Liquid line temp: 64*F
Suction line temp: 61*F
Superheat: 51*
Subcooling: 8*
Outdoor ambient: 60*F
Indoor ambient: 70*F

Trane R410a system

Model: 4TTR3036E1000AA
Serial: 1410386J3F

Have at it

 

What do you have for head press control?

 

Sorry for not knowing but what is that? Example?

 

I once almost got fooled by a YORK , same pressures as you have , and I found the unit had a 2 stage compressor ( never seen one before) and the board had it stuck in 1st stage. I bridged the board 1st and 2nd staqe , fired it up and pressures were fine. I have no idea how the compressor can have 2 stages , but it did

 

On a PERFECT system, what is the PERFECT head press on a 72*day? 72* ambient is typically the lowest ambient in which AC is used, as in OPEN THE WINDOW. What is the minimum head press that a Carrier MotorMaster(head press control device) is set for? It's 95* SCT! What is the minimum head press that the ORIGINAL Alco HeadMaster maintained for r12,r22,r502? Its right around 95* SCT. What is a cond fan cycling control set for ? Its right around 95* SCT +- a little. On those "charging charts" that many units have, what is the head on a 72* day?

Something like that!

 

I have a chart on this phone from a unit and it tells me that with a 65 degree liquid line temp with 10 degrees design subcooling the pressure should be 218 psig. So I'm off by 8 psig.

 

This is a r410 system right ? For years and years on a r22 system on a 72* day you added 25*to the ambient and you got the matching CT that you used your w/ the p/t chart to see what the head was supposed to be. So 72+25=97CT, and the p/t chart shows a press of 186psi or so on that 72* day. Then on a 95*day (the typical highest temp we get on LI,NY,,Ct,,R.I, Jersey) you add 30*. so ,95*+30*=125* SCT. So,on a 95* day you should have a r22 press of 276psi or so. The higher SEER stuff has dropped that adding of 30 to the 95*day down to 25* or even 20* on an ULTRA hi efficiency r410 system. So , on any decent 410 unit the same rules still apply and work.I think!

 

Haha ok I'll except that one.

I should change my post to never having a lower then ambient liquid line, Unless your severely under charged or Its raining :gah:

 

He never said it was below ambient just sweating. Maybe the basement had a higher wb than outdoor conditions unhooked drier vent ect

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That's what I was probably seeing.

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Trane 2 stage compressors have a secondary wire harness on the opposite side of primary harness of compressor(2 white wires). If it has second stage, you can verify it by tracing white wires to the DC bridge board in control panel on a little black square. There is a yellow and blue wire on this bridge and if you get 24 volts AC at blue and yellow, AND 24+- volts DC on the white wires, it's calling for second stage. You should check in 2nd stage if possible. Also, you can pull yellow or blue off DC bridge and see if pressures change. If it's single stage, bad TXV and I agree with possible low charge.

 

Thanks for that tidbit I see those a lot. Ever replaced a black box?

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I've replaced one bridge. It operates the solenoid inside the compressor to engage the second stage plate. I've found that the solenoid in the compressor goes out more often than the bridge and there's only 1 fix, new compressor .

 

Check temp drop across drier..., likely it is a blocked drier, seen it several times!