TXV not set properly?

Paul S_3

I went on a job earlier today new 2 1/2 ton r-410a system w/txv, it was undercharged, I found refrigerant leak at filter drier, repaired leak, evacuated to 500 microns etc,added refrigerant, charged to 12f subcool, problem is that my temperature split is to low, 14f (75f/61f)I checked my superheat 26f, line temp 61f ,saturation temp 35f. Am I missing something? Or should I go back and try adjusting txv? Thanks Paul s

Techman

TXV setting

The TXV has an adjustable SH stem? What brand of equipment?Why was the system charged to 12* of SC?The SH reading, was that at the comp or at the TXV thermal bulb? How long is the lineset ? Is evap above the cond unit, how many feet? Your readings were at startup of system or was unit running for hours?Indoor/outdoor temps? How did you verify that the LL was full at the TXV?

Paul S_3

txv

I believe the txv does have an adjustable stem, equipment is carrier, 12 f subcool was on condensing unit nameplate, outdoor temp was 80f,superheat reading was at condensing unit, line set is about 20 ft and condenser and evaporator are about the same height, readings were after the repair and system was running for a half hour Paul s

Techman

TXV setting

Morning Paul, I think either SH setting, undercharged,restricted TXV. I spoke w/ several mfrg's and the SC # that they stamp on their nameplates is for the "factory pre-charged refrigerant amount" which works with their "factory lineset length", vertical or horizontal !.  Now being that your system is almost horizontal the SC would be the same.So, assuming a 15' LL (as per factory) then the actual 20' LL was vertical ,then you'd need a little more SC ,say, 121/2* - 13*-14*-16*. Now a backward way of looking at the SC on a horizontal run , is, the LL is over SC'ed! The system is KindaSorta overcharged! The LL will be full at the TXV at 3*-4*-5* SC. You can call Carrier,Trane, Nordyne. How about a 40' vertical rise! That 12* doesn't count.

meplumber

Very well put Terry.

With a lineset that short, why not just calculate it and charge by weight?  You cannot go wrong charging by weight.



Up here in the great white north, we have to do that more often than by SH or SC.  Since the charts all stop at 50*, we wouldn't be able to charge but a few weeks a year without weighing it in.



I think that you are overcharged.  There is a slim chance that you have a restriction, but I would tell one of my guys to pull the whole charge out and weigh it in for the 20' lineset and then reevaluate.  Especially since you have no height difference to worry about.



Good Luck

Paul S_3

txv

How would I weigh it in by line set length? Do I call the manufacture for that? And how does height affect the charge? Thanks Paul s

meplumber

Weighed Charge.

Paul,  you would use a chart like this one.  All small tonnage units come precharged with enough refrigerant to cover the matched evap coil and a 15' lineset.  There will be a factory charge weight on the condenser.  You then use a weight chart to figure out how much extra to add for the additional lineset length.  See below:

Techman

TXV setting

This is where I have a little problem w/ weighing in the charge. On a horizontal LL ( and vertical up to the mfrg lineset of 15')  I agree w/the weighing way. Now ,KindaSorta, a 40' horizontal LL will have ,up to, 12* of SC, which is equal to the bottom 3 passes of the cond coil being 100% full of liquid Freon ,about 4* SC per pass. Now go vertical 40' w/ the same 12* SC ,same charge, and there will be activity (bubbling) in the LL near the top of that 40' rise and all the way to the metering device . Adding extra Freon to shrink those bubbles will also back up some of the Freon in the cond coil raising the liquid level up to the bottom 4 passes w/ 16* of SC , then there will be a full LL at the TXV. KindaSorta like a hydronic baseboard 4 story system.

unclejohn

Did You

Remove all the refrig before you fixed the leak or did you pump it down and then pull a vacuum on the line set and coil?

hheaddon

bad txv

With 12 s/c that should be plenty. Is it a danfoss valve by chance? There is a lot of failing TXVs in that brand that has been showing up lately. Same valve being used by a bunch of diff mfrs, some distributors can not find the replacements, end up giving out new coils just to get the valve.

Spence

Post-leak Operation

You did not mention air flow. With a low TD and high superheat, that is certainly something of importance.

icesailor

TXV Valve:

Is this valve the same as a EEV (Electronic Expansion Valve)? That is controlled by a FM EVC Board?

I had a new system installed in February, 2014 that never really worked as well as what it replaced. Then about a month 3 weeks ago, the system stopped cooling completely. This EEV closed completely and wouldn't pass liquid. When the wires to the EEV were disconnected and whatever else needed to be fixed, the valve manually opened. and the unit works now better than it ever did. Parts were ordered, thermistors. The most important wire was way to short to reach the FM Board, because originally, the FM board was mounted up in the space where the heat strips are. Now, it is down in the blower cabinet.

The Troubleshooting Detective in me thinks that the FM board was mounted at the top and suffered from condensation (maybe). Where the thermistor would reach. When they moved the board down. it is too short. They didn't send the correct one. The correct one was ordered and I think a FM board. The tech and I decided that something odd was going on. I read about this valve issue and mentioned it. But I don't know if we are talking about the same issue.

When the system was new, it always seemed like this EEV was not fully opened and didn't modulate. The suction line was always almost as warm as the liquid line. Once the connections on the FM board were disconnected, it started to cool better and the suction got cold and would get condensation outside at the compressor. I've waited over 10 days for the next round of parts. When it takes this long for parts, it usually means that there is a shortage.



And we ALL know how willing large manufacturers are to tell that there is a major problem with a component. Think GM and their faulty ignition switches.

Spence

TXV

Use your manufacturer's specifications for charging beyond the factory charge of 15' of tubing and the smallest AHRI matched coil.

John Mills_5

The TXV problem is NOT Danfoss, it's everybody. Seems a chemical they started putting in Copeland and Alliance (Trane) compressors cause the TXV to gum up. That causes high SH and low suction plus low TD. Now the manufacturers are saying get some AC Renew or the like (Trane has their own number) and inject in the system and that should eventually get the TXV working again.

Don_197

This is indeed an industry wide issue on 2-3 ton R-410a systems using Copeland Compressors. Rheem/Ruud have the easiest least expensive fix......copied and pasted below for your convenience. a little light reading if you will: 8-) Don

September 5, 2014
Dear Valued Customer:
We have received the following update from Rheem regarding the industry wide TXV issue:

"Rheem has identified potential root causes of the field reports where the TEV fails to maintain design superheat.
To recap prior bulletins, as previously reported analysis shows the TEV is not the root cause of this issue. We believe the source of the problem is a chemical substance originating from the compressor.
We have been working with Emerson Climate Technologies to revert back to manufacturing processes in place prior to when the TEV sticking issue started to appear. All residential condensing and package units will be manufactured with compressors utilizing these earlier manufacturing processes no later than September 10th, 2014.
Rheem has aggressively tested system additives to resolve the superheat drift issue. Early tests and field reports have shown favorable results with the Nu-Calgon's AC Re~New additive (Rheem Part number 4057-55). In known superheat drift situations, Rheem suggests the use of this additive will be an effective alternative to replacing the TEV. Note, our testing shows no benefit in using activated charcoal type filter driers with this additive. No harmful system effects have been observed with this additive, and Rheem continues to work with component manufacturers to assure long term reliability.
At this time, Rheem will support the use of the Nu-Calgon's AC Re~New additive in systems with outdoor unit serial numbers in the date code range of 4013 to 3714 that exhibit superheat drift without voiding the factory warranty.

An allowance is available for the addition of AC Re~New additive to systems that exhibit this phenomenon."
Rheem will provide the approved Nu-Calgon additive and a $100 labor allowance for the affected units in the serial number ranges from 4013 to 3714. This allowance and program is effective from September 2, 2014 and will terminate on August 31, 2015. The allowance and program does not include any tools and is not retroactive.
Although we do not stock a significant amount of the Nu-Calgon additive, we are diligently working with Rheem to obtain an adequate supply, which will be available to you as soon as possible.
We appreciate your patience regarding this matter and your continued support of Gemaire.

If you have any questions please contact your Territory Manager or Regional Manager.

Eugene_Silberstein

Thanks for the information Don!

JUGHNE

Is this strictly a 410-a issue?
Or would a new R-22 Copeland replacement compressor also would have had the problematic chemical added to the oil?

I have a 15 year old R-22 heat pump/AC with the symptoms of low suction pressure in cooling mode. (Plugged TXV??)
The compressor was changed August of 2010 and problems started 4 years later. Or would they have showed up early??

Another job I installed was a 410-a heat pump system 9-2010 and had to replace the TXV on 9-2012. (2 years operation) The supplier was quick to send out a complete coil with new TXV installed as the exact replacement TXV was not available. I was impressed with the warranty response of no charges for complete coil.
(This type of service is what keeps you buying at the same wholesale house)

GW

As mentioned, why not look at air flow? Some installers are absolutely clueless that air flows need to be adjusted, especially when the blower is rated for more capacity than the outdoor unit.

Gary

JUGHNE

Thanks for the reply. The problem system (R-22) has had the same air flow system unchanged since new install in 1999. I will look again to see if any factors have changed.

Question on the design of the inside TXV, there is no obvious external check valve visible, I assume that this TXV would have an internal bypass for the heating mode.
If dry nitrogen was back flowed thru suction line would the N2 flow thru the screen of the valve to clear any debris? Or does the by pass flow around the screen rather than thru it?