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The purpose of measuring sc is to ensure we have a solid column of liquid for the TEV/TXV. So we are measuring the degrees below saturation point for the given refrigerant, with this we ASSUME that there is liquid for the valve. Since the valve is in the evap, a lot can happen on the way from the condenser to the evap. Temp rise in an attic installed lineset, of a rooftop lineset, kinked lines etc.

The fact that Goodman's valves are adjustable surprises a lot of folks I work with.

I have learned a lot from this site. How to fight with ya'll has never been my goal.

Originally Posted by riderman

Just wondering here...If the SC and SH spec is 7-9 degrees and I'm sitting at 11-12 degrees, what is the consequence? I'll fix it, but it seems a lot of systems require around 10 degrees anyway.

To answer your question, none. Understanding the operation and flow of refrigerant is important and there is a misconception it appears of what a TXV does. Although TXVs aren't utilized as a capacity control device, in essence that's what they do (to a certain degree and within limits). They control flow of refrigerant based on SH set point (not SC). By modulating the opening of the orifice (in oppose to a one size fixed orifice) refrigerant flow through the evaporator will vary. Under high demand/ high heat load, your SC will drop ( maybe even below these rule of thumbs or factory recommendations) as system SH setpoint is trying to be maintained. On the contrary, when there is a low load ( for whatever reason) TXV is going to reduce flow causing SC to be above rule of thumbs as refrigerant will stack in the condenser. This could even result into driving your head pressure up as, just like a restriction, you have less available space in the condenser to reject heat. I would still be very curious for someone to give a play by play on adjusting TXVs to accomplish SC first and then charge system to achieve SH. I guarantee you'll be readjusting that TXV.

They call it a superheat spring for a reason on txvs...adjusting the slring adjusts the sh.

Lack of sc can also be from a dirty condenser.

Sent from my HTC One S using Tapatalk 2

Just wondering here...If the SC and SH spec is 7-9 degrees and I'm sitting at 11-12 degrees, what is the consequence? I'll fix it, but it seems a lot of systems require around 10 degrees anyway.

Originally Posted by danielworkerbee

I read the instructions before I adjust the TXV, but seems to me the opening or closing of the valve changes both the SH and the SC.
I believe you should adjust for the SH first then fill till proper SC.
luck dan

It will affect both but a TXV is designed to control superheat and not subcooling. The bulb and external or internal equalizer work in combination to sense and control superheat, the effect on subcooling is a passive one only. Use it for what it was designed for and your life will be easier.

Mark Beiser's post is the correct way to do it, but if you want to skin your cat differently, have fun.

Have to remember that your tag says regular guest so we that don't know you assume homeowner with a set of gauges and a few tools.[/QUOTE]


It's all good. I work for Uncle sam on this equipment and have several EPA certs and such. I sometimes ask too detailed info in the oipen forum and rightfully get cautioned and was suprised at getting a little flack for what I thought was a simplified no detailesd question. I see yall's point.

Mark, Yes you are correct! I read mis-information from another source. Thanks eveyone for the responces. As you know, it is hard to find correct information sometimes. Thanks again, I ment no offence to anybody, so I hope no one took any.

Originally Posted by Install WIZ

If I remember right. U should be about 5-7 for your sc. Adjust accordingly. Then if your SH is high add refrigerant to get your correct reading. If both are low or high to start with you will have to adjust your charge to get close before you adjust your txv.

Yep.

Originally Posted by riderman

You are right, the unit was not stabilized, I'll check it in the morning. I did not give detailed info and I did not request it. The pressure left in the lines and AHU coil after the pump down did not amount to a good fart, let alone to any amount of refrigerant loss. Not to be a S....A.. here, but why would I ask about a TXV adjustment if the TXV was not adjustable? I stated SC was 6 degrees below spec....,maybe that was unclear in my first post. Yes, I work in the field. I think we will stop this thread now. I just had a simple question for what for some should be a simple answer.

I have no idea who you are, what you do, what you know, or otherwise.. Your next question could have been how do I adjust the TXV for all I know when you never listed the TXV you installed
The last thing you want to do is go twisting on a TXV adjustment without first seeing where you stand on everything else and considering I don't know who did what to the charge because the TXV was malfunctioning before it was discovered bad, finding what the SH, pressures, etc is where I go before I ever adjust something as much of a PITA as a TXV.. Will just make your life easier. Have to remember that your tag says regular guest so we that don't know you assume homeowner with a set of gauges and a few tools.

Originally Posted by beenthere

In the install instructions for some Goodman/Amana units, it tells you to adjust the SC of the TXV, and then adjust charge to get the SH where it should be.

OP. Recover the charge and weigh it to find out if it has the correct charge. Then use the refrigerant you recovered to recharge the unit. No need to use virgin.

If I remember right. U should be about 5-7 for your sc. Adjust accordingly. Then if your SH is high add refrigerant to get your correct reading. If both are low or high to start with you will have to adjust your charge to get close before you adjust your txv.

I mean no offense to my esteemed colleagues with my previous post! All of that information does come into play, Sometimes we forget how we need to be flexible in this industry. There is rarely a system that has been designed by us, manufactured by us,installed by us, A lot of times it is an air-conditioning system added to ductwork that had never been intended for air conditioning and was installed 40 years ago, That is the case with my house! I have a 20 x 8 supply 20 bye eight return from one end of the house to the other four-inch Spin-ins are the only supply to each room My Delta T was too high, I know my ductwork is too small, increased airflow to accommodate! It's a little noisier than I would like, but I'm not in a position to rip down an entire finished basement at this point to make some design engineer happy

Originally Posted by joegrind

That's funny Riderman! About a week ago I tried to give a simple answer to a simple question similar to like you're asking and just got railroaded. He asked a simple superheat question that required one answer yet he was bombarded with did you pull out your boomerang? did you use the yellow screwdriver or black one? did the homeowner have blond hair black hair? did you use a sling psychrometer that was recently calibrated by NASA,? Did you take into account the solar flares that were happening that afternoon? Anyway you get my point! If you're superheat is okay then add a little bit of refrigerant and see if the subcooling comes into line with the manufacturers chart!! All things being equal you might only be lite by a pound or less, If you do need to recover what's an extra pound!

You forgot, Al Gore said Global warming effects SH and SC.

Originally Posted by riderman

You are right, the unit was not stabilized, I'll check it in the morning. I did not give detailed info and I did not request it. The pressure left in the lines and AHU coil after the pump down did not amount to a good fart, let alone to any amount of refrigerant loss. Not to be a S....A.. here, but why would I ask about a TXV adjustment if the TXV was not adjustable? I stated SC was 6 degrees below spec....,maybe that was unclear in my first post. Yes, I work in the field. I think we will stop this thread now. I just had a simple question for what for some should be a simple answer.

That's funny Riderman! About a week ago I tried to give a simple answer to a simple question similar to like you're asking and just got railroaded. He asked a simple superheat question that required one answer yet he was bombarded with did you pull out your boomerang? did you use the yellow screwdriver or black one? did the homeowner have blond hair black hair? did you use a sling psychrometer that was recently calibrated by NASA,? Did you take into account the solar flares that were happening that afternoon? Anyway you get my point! If you're superheat is okay then add a little bit of refrigerant and see if the subcooling comes into line with the manufacturers chart!! All things being equal you might only be lite by a pound or less, If you do need to recover what's an extra pound!

Originally Posted by riderman

Mark, I had to go back and read more info. I guess you could be right, but you could be wrong. In a single stage application, If SH and SC both are low or high, it say's adjust the TXV. It has more information.

I'm right, no doubt about it.
Reread the instructions you are looking at, as you are misinterpreting them.
SC is adjusted by adjusting the charge, SH is adjusted by adjusting the TXV.

Originally Posted by beenthere

In the install instructions for some Goodman/Amana units, it tells you to adjust the SC of the TXV, and then adjust charge to get the SH where it should be.

Not unless there are some misprinted instructions floating around!

Direct from the SSX14 manual:

"3. Check subcooling and superheat. Systems with TXV application
should have a subcooling of 7 to 9 ºF and superheat
of 7 to 9 ºF.
a. If subcooling and superheat are low, adjust TXV to
7 to 9 ºF superheat, then check subcooling.
NOTE: To adjust superheat, turn the valve stem
clockwise to increase and counter clockwise to decrease.
b. If subcooling is low and superheat is high, add charge
to raise subcooling to 7 to 9 ºF then check superheat.
c. If subcooling and superheat are high, adjust TXV
valve to 7 to 9 ºF superheat, then check subcooling.
d. If subcooling is high and superheat is low, adjust
TXV valve to 7 to 9 ºF superheat and remove charge
to lower the subcooling to 7 to 9 ºF."

The same instructions appear in the installation manuals for all of their outdoor units. The 2 stage units have the additional stipulation that the TXV and charge are to be adjusted in 1st stage cooling.

Originally Posted by Mr Bill

I can't even remember the last time I adj. a txv on a res. system, but I want to say in the late 70's, and that was to only get the way out of wack SC and SH correct.

On Goodmana equipment, I've found that the TXV has to be adjusted at least half of the time when doing the initial start-up.

I read the instructions before I adjust the TXV, but seems to me the opening or closing of the valve changes both the SH and the SC.
I believe you should adjust for the SH first then fill till proper SC.
luck dan

Originally Posted by git-r-dun

I wonder what the logic is behind that. It's not adding up in my head how it is recommended on an undercharged system to increase TXV SH setting in order to get subcooling and then magically expect the TXV to maintain a reasonable superheat once refrigerant is dumped into it.

Originally Posted by beenthere

In the install instructions for some Goodman/Amana units, it tells you to adjust the SC of the TXV, and then adjust charge to get the SH where it should be.

I wonder what the logic is behind that. It's not adding up in my head how it is recommended on an undercharged system to increase TXV SH setting in order to get subcooling and then magically expect the TXV to maintain a reasonable superheat once refrigerant is dumped into it.

Originally Posted by beenthere

In the install instructions for some Goodman/Amana units, it tells you to adjust the SC of the TXV, and then adjust charge to get the SH where it should be.

I can't even remember the last time I adj. a txv on a res. system, but I want to say in the late 70's, and that was to only get the way out of wack SC and SH correct. [/QUOTE]

Originally Posted by mark beiser

You don't adjust the TXV to change the subcooling...

In the install instructions for some Goodman/Amana units, it tells you to adjust the SC of the TXV, and then adjust charge to get the SH where it should be.

OP. Recover the charge and weigh it to find out if it has the correct charge. Then use the refrigerant you recovered to recharge the unit. No need to use virgin.

Originally Posted by riderman

You are right, the unit was not stabilized, I'll check it in the morning. I did not give detailed info and I did not request it. The pressure left in the lines and AHU coil after the pump down did not amount to a good fart, let alone to any amount of refrigerant loss. Not to be a S....A.. here, but why would I ask about a TXV adjustment if the TXV was not adjustable? I stated SC was 6 degrees below spec....,maybe that was unclear in my first post. Yes, I work in the field. I think we will stop this thread now. I just had a simple question for what for some should be a simple answer.

rofl... sorry I read your post off my phone...didnt see the part about you saying the subcool is low by 6 degrees. LOLL , good luck.