I would like to know also.

 

Moved to tech to Tech forum.

 

You would have to contact the design engineers.

"Different manufacturers have various methods for determining target subcooling. For superheat, most manufacturers use the same charts, but this is not true of subcooling. There is no substitute for having the manufacturer’s subcooling chart."

Source:
http://www.fieldpiece.com/tech-arti...t-and-subcooling-tools-troubleshooting-guide-and-faqs-ssx34-asx14-asx24-ash3#11

 

You can download this book it has a superheat chart, its FREE

http://shop.rdholder.com/Troubleshooting-an-Air-Conditioning-system-Troubleshooting.htm

FREE articles on Superheat, Subcooling and A/C Troubleshooting. For the FREE downloading of the articles go to Book and Papers on HVAC on the main page, put them in to the cart then, you must click on the PRINT AND CALL button for payment at check out. This method allows me to process your downloading at NO CHARGE.

 

Help if how to download when you living in Asian Country. Also not allow to Check-out



Hi,
Help if how to download when you living in Asian Country. Also not allow to Check-out using Paypal.
Many Thanks,
Rodel

 

If it's not posted on name plate I have always used 10 as you stated.

 

The goodman units that I've installed all required 7 sc,carrier has it written on their data plates,but from what I've seen if you can't get the info,10-14 seer,10 is a good rule of thumb,some higher 15 seer units ask for 15 sc

 

correct me if i am wrong but the 10* has to be read at the evaporator not the condenser for a true reading. if you have a long lineset that number may be alot higher at the condenser.

 

Yes I believe it is cracked you need to check the super sweet how cute is that a liter oil...

Ok i will have to type this out. Voice recognition sucks on my tablet. Yes i believe you need to technically read super heat where it exits the evaporator coil.

Tony Stone
Please excuse my brevity, sent from a piss poor quality mobile "operating system", aka "Android". TapaTalk application is okay I guess...

 

A forum member directed me to a phone app called hvac buddy. It has a target subcooling formula built in but I've yet to try it. If you look in the right location you can avoid paying the 10 bucks for it

Sent from my HTC Sensation 4G using Tapatalk 2

 

A forum member directed me to a phone app called hvac buddy. It has a target subcooling formula built in but I've yet to try it. If you look in the right location you can avoid paying the 10 bucks for it

I'm not sure how much I'd rely on that for anything, it certainly isn't intended for TXV equipped systems.

 

Yes I believe it is cracked you need to check the super sweet how cute is that a liter oil...


lol...

 

What we do when the name plate doesn't have any of the charging info we use HVAC buddy. You type in the system information and it tells you what it should be for subcool or superheat. Its not the best thing but when you don't have any manufacturer specs on subcooling or superheat it definitely gets you into the ball park.

 

You would think the manufacturers would provide that info on their web sites

 

You must have enough subcooling to offset the pressure drop of the liquid line, plus a couple of degrees as a buffer, or the system will not work correctly.

A solid column of liquid at the expansion device.

 

Due to the higher effs/ smaller evap coils volumes, systems are getting a lot more touchy about charge.

They'll work fine in cooling, them the head pressure goes crazy in ht mode. much less forgiving on some. One of Lennox guys said can be little as 10 oz on charge can throw off.

 

All way use manufacturer specs on subcooling or superheat if you have them but if not.

for Superheat:

Always check for proper evaporator air flow when charging a fixed orifices superheat, be sure to use the charts that each manufacturer’s can supplies for the system that is being charged or a formula for fixed orifice is.

{((3xindoor wet bulb)-outside dry bulb)-80}/2

An A/C with a Thermostatic Expansion Valve (TXV) is charged to the subcooling of the liquid line leaving the condenser because the superheat is fixed by the TXV. The superheat is specified by manufacturer and is normal between 16 degrees +- 2ºF in most residential air conditioning systems. Subcooling is the amount of liquid held back in the condenser. This allows the liquid to give up more heat, below saturated pressure- temperature. For every one degree of subcooling at the same condensing+ pressure, capacity will increase .5 percent. See the chart that I developed for HVACPro app. The subcooling will change at 96 degrees out side and 52 degrees wet bulb inside from 14.5 to 4.5 when the wet bulb inside is 88 degrees. Increasing subcooling with an increase of discharge pressure and compression ratio, decrease capacity. Add 5 degrees of subcooling for every 30 feet of liquid line lift to prevent the formation of bubbles, flash gas due to the pressure drop.

 

Look at my profile for my e-mail and I will send it to you

Roger

 

With a fixed orifice you don't charge to subcool, you charge using superheat. If you want to go through the process of getting a hold of tech support for whatever company's equipment you're installing, they can tell you the subcool, but you can avoid all of that by charging to superheat. Any modulating valves you want to charge to subcool with a range of 8-12° unless manufactures specifications say otherwise.

 

Your 13 years late!

 

This is anecdotal; but I have observed that on current TXV systems the design subcooling tends to be within a couple degrees of the design superheat. That has become my rule of thumb when necessary.

I almost never check liquid line pressure on a non-TXV setup. I have no curiosity about the subcooling and don't want to remove any more refrigerant than necessary.

 

Subcooling can vary greatly compared to ssh, especially on commercial & industrial products. Sc is based on refrigerant, metering type, ll pressure losses, elevation differences, load & head pressure dynamics.

Ssh protects the compressor. While providing maximum evaporator efficiency. Will vary with the type of evaporator, compressor, application & control valve.

Always check ssh, dsh, sc, & ll approach as a cross reference on readings of all systems.

Orifice systems are critical charge systems and must be accurate to achieve rated capacity & efficiency.

 

However, if the previous tech overcharged the system sub cooling would most likely show that.

 

If the system is charged by subcool, the target value is printed on the data plate and usually with some kind of degree of variance too (like +/-2 degrees for example)

 

If I find a TXV system with low subcool, would it be useful to measure liquid line temperature drop to check for flash gas?

 

I try to measure sub cooling right at the inlet of the TXV. That will tell you if it's flash gas going into the valve or not, as if the data plate requires a specific sub cooling for that particular valve anything drastically less will run an inherent risk of flash gas and "hunting".