Suction line temp 15 SEER

[douknowq]

I can't get a good temp on my suction line. i've ran the head from 200 to 375 all with about the same suction pressure 75. seems like no matter what i still get about 63 degrees at best. its 76 indoor 92 out new system super clean new filters. suction at 75 refrigerant is around 45 so i would like to get 55 (10 super) just cant seem to acheve it. I pulled a nice deep vacuume when i installed it a year ago. did not put in a filter drier or sight glass should I?

[Chuck Harwell]

Let system run for a couple days.Check entire system again.

[greggg1]

whats subcool ? possible highside restriction

[skippedover]

Sounds to me like you have a TXV for a pressure reducing device. If it's working correctly, you'll get whatever superheat it's set for. You didn't mention the superheat so I'm presuming you either haven't take it or don't know how. Either way if you've got a TXV, the ONLY TWO ways to charge the system are to recover the full charge and weigh in a new one. The other way is to use the sub-cooling method, which is the preferred method for an operating machine. There's no way a fixed orifice (piston) would deliver the same suction line pressure under the varied high side pressures you've stated and if you had a compressor valve problem you surely wouldn't be able to varay the head pressure the way you've stated. So I'm betting you've got a TXV on a piece of high efficiency or R-410A equipment and don't know it.

[douknowq]

Yep, txv - American standard TWE-E variable speed. I realize i should be checking sub cooling not superheat but when i charged the system using subcooling it was worse 68 deg on suction.

[douknowq]

also there should not be any restriction. i ran the copper myself, no kinks only long 90s inside of liquid line be burred also. swedged fitting not couplings

[skippedover]

You HAVE to use the manufacture's charts for accurate sub-cooling. Having said that, if it's an R-410A system, I've never had any luck trying to charge accurately without some load on the system and at leas an OAT of 70F, despite the manufacturer's claims of being able to charge down to 55F. Horsefeathers!

[mark beiser]

You are working on a system with a TXV in the indoor coil, charge by subcooling, the TXV will control the superheat.
Check the manufacturers charging instructions, but in most cases, 10-12º of subcooling is about right.

FYI, the place to check the suction line temperature to get the superheat on a TXV system is at the outlet from the evaperator coil, usually it should be about 10º. If you check at the outdoor unit, it will be higher.
A 63º suction line at the outdoor unit with a 45º saturated temp is pretty normal for a TXV equipped system IMO.

[skippedover]

If you absolutely can't get any better reading than you're getting, first check the sub-cooling. After that, I'd be on a failed TXV. We had a similar circumstance a couple of years ago with a Trane TWE-E unit. I had three different techs on the job before I caught the TXV not working. We replaced it and the system ran great after that. We still ended up replacing the stupid air handler because the client wanted a 'matching' unit and while the CFM's were only different by 25CFM, he wanted the next higher size air handler. So we changed it out for him. It made not a hoot of a difference in cooling his home. Just cost us a lot of money and gave him piece of mind, which I guess is most important. I think.

[douknowq]

had plenty of load today thats why i was out there unit would not come down pasr 77 indoor. it was about 96 outside. anyway i charged it to the chart on the paperwork with subcooling months ago. still not getting a good temp split when real hot.

[douknowq]

Mark, are you saying thats as good as it going to do on a day when it almost a hundred out?
I charged a unit yesterday almost as hot out. a piece of crap 8 seer had 5 degree superheat froze the poeple out.

[mark beiser]

Yep, txv - American standard TWE-E variable speed. I realize i should be checking sub cooling not superheat but when i charged the system using subcooling it was worse 68 deg on suction.

Pull out the Service Facts sheet in the outdoor unit and open it up. in the middle of page 3 there is a charging chart that uses LL temp and liquid pressure and has a curve made up of 3 lines.
at the bottom right there is another graph for refrigerant line length and lift that tells you which curve on the chart to use.
Plot your liquid pressure and LL temperature on the graph. If it falls above the curve, remove refrigerant. If it falls below the curve, add refrigerant.
Recheck the liquid pressure and LL temp every time you remove/add refrigerant because the spot on the graph will change.


Once you have the charge set per the charging instructions, flip over to page 4, the back, of the Service Facts and look at the performance graphs there.
If the indoor unit listed over the performance graph isn't the one you have, look further down the page at the list of indoor units. Pick the one you have and note the correction factor + or -.
You need the wet bulb temperature for the air entering the indoor coil, the outdoor temperature, suction pressure and liquid pressure.

Plot the outdoor temperature and the wet bulb temperature on each of the appropriate graphs, then add or subtract any correction factor.
The actual liquid pressure should be within 10 psig or the chart, and the suction pressure should be within 3 psig of the chart.

If all of that checks out, button the unit up and stop worrying about the suction line temperature. :p

[mark beiser]

Mark, are you saying thats as good as it going to do on a day when it almost a hundred out?
I charged a unit yesterday almost as hot out. a piece of crap 8 seer had 5 degree superheat froze the poeple out.

Fixed metered system, if it was 70 out they may have had 25+º of superheat, or if it got hotter out, they may have 0º of superheat.

Unlike a fixed metering device, a TXV will maintain a consistant superheat across a variety of load conditions. Adjusting the refrigerant charge will make little difference in superheat, unless you grossly under or over charge it.

As I mentioned before, check your suction line temperature right where it exits the air handler, typically it should be 10º above the saturated temperature at that point in the system.
If you are checking the temperature at the outdoor unit, the vapor has the entire length of the suction line to pick up additional superheat.

[douknowq]

Thanx, i'll reread the chart tomorrow and put it back to the correct subcooling. then i will go in the attic and check the temp @ A/H instead of cond. thanx a lot let you know what happened tomorrow. going to bed good night

[mark beiser]

Get the wet bulb temp of the return air entering the indoor coil, so you can check the performance chart, while you are up there.

[a314sparky]

While I dont see all the info to diag correctly I would guess you have a TXV problem. If a TXV is failing you will be unable to charge by subcooling. Best advice get it close and check the TXV for failure via superheat at the acoil Tranes usually have a service valve at the coil. It should be about 15 dgrs. But what your realy looking for is a uneven hunt going greater than 20 dgrs sprht. or less than 5 dgrs. Take your time and watch it carefully I believe you will see what I am talking about.

[douknowq]

OK, Im charging subcooling as we speak, using the manuf. chart. I installed a sight glass and drier. Vaccuumed and preeure tested opened valves and charged with vapor only untill the sight glass cleared up. pressures are well below charging specs. going to let it run for 20 min before adding more gas.

[douknowq]

Well done charging to chart inside unit, subcooling. Running great, I think the drier helped. I'm getting much colder suction line temp even at heatpump, 10 degrees colder at evap. thankx everyone. going to start using driers more often.

[douknowq]

OK, have a new question...... Amer Strd. 15 SEER has been running fine for 3 years..now sub cooling is WAY off. Suction line temp is 70 (at condenser) house is 79 deg. suction pressure and head pressure are where they should be on the chart that came with unit. lowered pressure and same line temp....added freon and same temp on line. I am hearing a whirling from the condenser.. sounds like it is by the txv... also the reversing valve is groaning when it switches over.

[beenthere]

Doug.

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