High super heat.

[AStudent]

fan is moving to much air.
Or a mix of underfeeding txv + extremly high humidity.

Indeed.....remember we check a TXV system with subcooling...if it's right then it shouldn't be refrigerant.

[Furlo]

Where do you guys think the best place to get my suction line temp at, next to the service valve, or near the evapcoil. I have always took my temp 6 inches from the service valve but I would like to know what you pros think. Thanks

[vstech]

the installation manual on most units asking you to test superheat state to get it 6" from the compressor... alternate location is as close to the condenser as you can. I like to take a reading on the suction service valve stub.

[dsprice]

Doesn't matter, a liquid column is a liquid column.

Make sure both coils are clean and check you amp draws. Be thorough about you airflow inspection and check for air leaks at you plenums. It's rare that an older unit needs a charge after working for years.

If all is good, adjust your fan speed 350 - 400 cfm's then charge your target superheat. Especially on high humid days. When you finish and check your subcool, it should go up only 1 or 2 degrees. More than that and I would question the txv.


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[Slayer0901]

Your subcool tells you if u have enough refrigerant in system your superheat tells u if your txv is metering correctly

[dsprice]

Doesn't matter, a liquid column is a liquid column

Sorry, nevermind that....misread you question

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[hvacvegas]

Indeed.....remember we check a TXV system with subcooling...if it's right then it shouldn't be refrigerant.

I kinda agree.

You ever:
get a install a new txv, charge the system, get correct subcooling, check your superheat. Lets say it's real high. Adjust txv, now your subcooling has changed.
Meaning, just because your subcool is correct, doesn't mean you have the correct ammount of refrigerant. When you adjust your txv to change your superheat, it changes the subcool also.

Also, on a side note, had this one happen to me last week:
Startup a system. Subcool is off. Look at superheat. way high. Off the cuff, alot of guys would think TXV shut closed.

Here's the jist. The unit is soooo undercharged, that even with the TXV wide open (which is should be to bring down my superheat), I'm not getting enough refrigerant through my evap.

I guess what I'm saying, is it's not as black and white as "if the subcool is good, then you have a correct charge, look elsewhere." By all means, if your subcool is fine, look elsewhere, but don't forget to re-check after you fix the problem.

[hvacvegas]

Your subcool tells you if u have enough refrigerant in system your superheat tells u if your txv is metering correctly

see above.

[timebuilder]

I kinda agree.

You ever:
get a install a new txv, charge the system, get correct subcooling, check your superheat. Lets say it's real high. Adjust txv, now your subcooling has changed.
Meaning, just because your subcool is correct, doesn't mean you have the correct ammount of refrigerant. When you adjust your txv to change your superheat, it changes the subcool also.

Also, on a side note, had this one happen to me last week:
Startup a system. Subcool is off. Look at superheat. way high. Off the cuff, alot of guys would think TXV shut closed.

Here's the jist. The unit is soooo undercharged, that even with the TXV wide open (which is should be to bring down my superheat), I'm not getting enough refrigerant through my evap.

I guess what I'm saying, is it's not as black and white as "if the subcool is good, then you have a correct charge, look elsewhere." By all means, if your subcool is fine, look elsewhere, but don't forget to re-check after you fix the problem.

Of course, it is important to note that you have to finish the pulldown event before you can have meaningful checks. However, if you have good subcooling on a TXV system during pulldown, you are already using refrigerant at your maximum rate, and no more will be needed when pulldown is finished. Subcooling will probably increase slightly. High superheat during pulldown is a normal condition.

[Glennhvac]

Could be too much air across evap. We see that so seldom and seem to be looking for ways to move more air more often than not.
I had a guy call last summer with problems cooling and especially humidity removal. He had one central return right off the top side of the furnace and supply air flow to die for. Too much air even on low speed. We taped a manilla folder over 1/2 the grille for a couple days and the guy was elated in the results.

A couple weeks later I went back, took some 16 inch flex off the top and snaked it around a bit in the attic and went with a ceiling R/A and a manual damper on the duct.
Air flow solved, and the bonus is he can actually hear the TV set now.

[superd77]

Could be too much air across evap. We see that so seldom and seem to be looking for ways to move more air more often than not.
I had a guy call last summer with problems cooling and especially humidity removal. He had one central return right off the top side of the furnace and supply air flow to die for. Too much air even on low speed. We taped a manilla folder over 1/2 the grille for a couple days and the guy was elated in the results.

A couple weeks later I went back, took some 16 inch flex off the top and snaked it around a bit in the attic and went with a ceiling R/A and a manual damper on the duct.
Air flow solved, and the bonus is he can actually hear the TV set now.

I may be misunderstanding your post... Did you restrict the return?? Or did you put a bigger return in??

[Glennhvac]

I may be misunderstanding your post... Did you restrict the return?? Or did you put a bigger return in??

The only way I could move less air with the furnace he had in relation to his cooling system was to cut back on the return some. He had great supply ducting and the return was for all practical purposes as if he was running it with the blower door off.

Later I relocated the return into the hall ceiling with flex duct and used extra as a muffler sort of. This was to quiet the darn thing so he could hear the tv.

[Slayer0901]

I kinda agree.

You ever:
get a install a new txv, charge the system, get correct subcooling, check your superheat. Lets say it's real high. Adjust txv, now your subcooling has changed.
Meaning, just because your subcool is correct, doesn't mean you have the correct ammount of refrigerant. When you adjust your txv to change your superheat, it changes the subcool also.

Also, on a side note, had this one happen to me last week:
Startup a system. Subcool is off. Look at superheat. way high. Off the cuff, alot of guys would think TXV shut closed.

Here's the jist. The unit is soooo undercharged, that even with the TXV wide open (which is should be to bring down my superheat), I'm not getting enough refrigerant through my evap.

I guess what I'm saying, is it's not as black and white as "if the subcool is good, then you have a correct charge, look elsewhere." By all means, if your subcool is fine, look elsewhere, but don't forget to re-check after you fix the problem.

I agree what u do to one side it will affect the other side