Low Delta T - pressure's say anything?

[ps2cho]

follow up on my last thread a few weeks ago...

Last year I had HVAC company put in (two) 3tn Trane XR16's and matched TEM6 air handlers. Fast forward a year later, and both units seem to be underperforming. I want to try and see if anybody could look at these pressures and tell me if anything seems off?

Delta T measured at plenum -- 12-14F, never any higher. Outside dry bulb 105F at condenser. Inside is 78F at return, 66F supply.

Our downstairs struggles during the day to get below 77F. I asked it to drop from 79 to 76 4hrs ago and it hasnt got any lower than 78F. Somethings not right. The only strange thing is that BOTH units have poor Delta T...

I have a photo of it outputting 20F delta T a year ago, so it did perform when new.

Any signs here that point to anything?

 

[danski0224]

Subcooling and superheat will tell the tale.

 

[brewchief]

Subcooling and superheat will tell the tale.

Yup, based on the pics assuming the thermometer is correct I see 14 degrees of subcooling and 30 degrees of super heat.

Subcooling looks pretty close but superheat seems pretty high for a TXV system

 

[danski0224]

My gauges do the math for me.

Why is the high side pushing over 400 and the low side isn't cracking 150? Seems off.

The stubby gauges look interesting, though.

 

[Snapped-off]

Head pressure seems pretty high. Is that normal for 105F?

 

[mustangacman]

Is the cond. coil dirty?

 

[ps2cho]

Is the cond. coil dirty?

Nope - fully cleaned last week. Removed the fan, foamed it and rinsed off thoroughly.

 

[danski0224]

I'd guess that there's ductwork in the attic and something is open. Or a building cavity used for ductwork.

Operating parameters need to be the same to compare air temperature differences at the evap coil.

The right way to do it is with enthalpy.

 

[ps2cho]

Yup, based on the pics assuming the thermometer is correct I see 14 degrees of subcooling and 30 degrees of super heat.

Subcooling looks pretty close but superheat seems pretty high for a TXV system

Thats what I thought too - but its weird that BOTH units have the same issue-low delta t, same pressures, same subcooling/superheat (within a few degrees). Temps should be right - St4 was calibrated in ice water, and its only 1F off another thermometer I have. Should be right.

My ask is because if the installers screwed up, I'd like to see if I can identify and make sure I dont pay out of pocket for their mess up.

 

[American Locomotive]

Check for a temperature difference across any visible filter-dryers. They can get plugged up on poor installs. Also 105 drybulb is pretty screamin' hot. Trane's published performance specifications are only at 95°F dry bulb.

 

[ps2cho]

Check for a temperature difference across any visible filter-dryers. They can get plugged up on poor installs. Also 105 drybulb is pretty screamin' hot. Trane's published performance specifications are only at 95°F dry bulb.

good thought - dont see any material difference across the filter/dryer after the access ports.

 

[fitter30]

44.7° suction pressure 130 lbs. Where are you taking super heat temp? Should be at the txv bulb. Bulb should be tight to clean surface on pipe and insulated. Ir thermometer shouldn't be used k type thermometer works well for surface temp. Txv takes a minimum of 20 - 30 minutes to settled down or after adjustment. Clockwise to raise super heat CCW to lower. After adjustment 10-12° recheck sub cooling.
www.amazon.com/Srutueo-Digital-Thermometer-Thermocouple-50-1300%C2%B0C/dp/B0D2GN7SR8/ref=asc_df_B0D2GN7SR8/?tag=hyprod-20&linkCode=df0&hvadid=693270340263&hvpos=&hvnetw=g&hvrand=4098445828087101302&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=200619&hvtargid=pla-2317283952708&psc=1&mcid=4393109f9f64353bbcf5aded02155212&gad_source=1

 

[danski0224]

I have yet to see an adjustable TXV on residential equipment.

 

[fitter30]

I have yet to see an adjustable TXV on residential equipment.

Haven't really worked on split system for at least 13 years ( retired). I've had a 4 ton trane package hp and 7 years ago put in two three head minis. 44years of running service 99% Sporlan. Biggest problem bulb not mounted correctly, bulb failed ( head), one with solder shut equalizing line ( new 100 t roof top one circuit) and valves that were over sized.

 

[brewchief]

I have yet to see an adjustable TXV on residential equipment.

Pretty sure goodman of all companies uses an adjustable txv, I think I have one to install next week so I'll look then.

It feels like a TXV that's starving the coil to me based on the reduced temp splits and the 30 degrees of superheat.
What are the odds that 2 TXVs failed in the same way at the same job? Maybe poor install practices plugged the screen before the TXV?

 

[danski0224]

Maybe poor install practices plugged the screen before the TXV?

Like no nitrogen purge?

Nah.