It depends on the lineset size and the length varies from manufacturer.

 

Dont charge by pressure, charge by subcooling or superheat depending on your metering device and according to unit charging chart.

 

This is true. When I charge a system with the units charging chart, I write on my ticket "Charged system to manufacturers specifications".
It makes me look really smart like I actually know what Im doing. Jokes on them though.

 

one unit is 7/8-3/8 and the other is 3/4-3/8 and both are about 75ft and the units suppossedly carry a charge for up to 15foot of lineset---which we all know is very seldom ever that short of a lineset--i do know all about the other ways of getting a proper charge,but was told by a fellow hvac tech today that you could use this formula(if that is the correct one that i remember being told)he is fresh out of hvac school and says that is what "the book says"--i am old school and have never did it that way---but was just wondering if there was any truth in this formula---thanks

 

Well, Its closer to 1/2 an ounce per ft not .06.your math is messed up I come up with 36 ounces (based on 60 extra ft). 2 lbs 4 oz. But besides that Ive always done it for 30 ft of lineset. so 45x.6=27 oz.
You should just use the charging chart, because now you've confused me too.

 

hey clintkennon --you sound just like me--lol

 

Gibson requirements

I often work with Gibson and Newtone units for which the documents state that their units come charged for a fifteen foot run of the recomended size lineset be it 5/8 and 3/8 or 3/4 and 3/8 and for either add 0.6 oz for each foot of additional lineset. I would think that would be pretty close for other brands assuming a normal lineset installation.

 

It should tell on the door chart.

 

I do the weigh in method to get me close then check it with the data plate on the unit.

 

are you talking about weighing it in with no charge on the unit--i know that the unit will say that it holds 90oz or what ever and you can just weigh it in if you have no charge on the unit---but i am talking about calculating to weigh in the differance for the extra lineset---thanks

 

ok--so would it be .6 or .06,because i was doing 50ftx.06=3lb,you are saying 50ft x .6=30oz--which would be 1.875lb?Is this correct as i admit i was not paying that much attention to him at the time i was told and may of had my figues wrong--thanks

 

Wheres the 50 coming from? 75-15=60.
But yes if you must butcher basic math 50x.6 would equate to 1 lb 14 ounces.

 

Most manufacturers call for .6 per ft over 15 feet of line set. This is per ft of liquid line , if 3/8 OD copper.

Also you will lose a percentage of capacity because of the length of the suction line and will have to up size suction and sometimes the liquid to keep the capacity up, depending on length per manufacturer specifications.

Example Only:

Goodman 5 TON Unit
Line Set Equivalent Length 50ft 75ft 100ft 125ft 150ft
suction line size 7/8: capacity .93% .91% .89% .86% .84%
suction line size 1-1/8: capacity .99% .98% .98% .97% .97%

 

Most manufacturers call for .06 per ft over 15 feet of line set. This is per ft of liquid line , if 3/8 OD copper.

Also you will lose a percentage of capacity because of the length of the suction line and will have to up size suction and sometimes the liquid to keep the capacity up, depending on length per manufacturer specifications.

Example Only:

Goodman 5 TON Unit
Line Set Equivalent Length 50ft 75ft 100ft 125ft 150ft
suction line size 7/8: capacity .93% .91% .89% .86% .84%
suction line size 1-1/8: capacity .99% .98% .98% .97% .97%

ok--i may of just opened up a can of worms that should of stayed closed--i know that to get the effieciancy that you are supposed to upsize the suction line--but for a moment lets just take that out of the situation and just say that we have 50ft extra lineset for a total of 65ft----ok now with that being said it then puts me back to square 1--you are saying .06,so is it .06 or .6?

 

I have delt with an American Standard dealer here local and with a question I always called then they have a program they put length and size and it tells you the additional amount of refrigerant to add. So you may check with your supplier. But always check the superheat and subcooling.

 

Its not a fixed amount per foot, as in, its not the same for all units, or size lline sets.

A York model, depending on size, will be.
.68, or .70, or .76
.68x50=30 ozs
.70x50=35 ozs
.76x50=38 ozs

Not a real big deal between .68 and .70.
But use .68 instead of the .76, and your a half pound low on charge.
Use .76 instead of .68, and your a half pound over charged.

Always check the manual.

 

It is a matter of physics. All tubing and piping will hold a specific volume of liquid based on the ID. It doesn't matter who manufacturers the equipment. If the tubing is 3/8, then the amount is the same. Using 3/8 LIQUID line, add
.6 ozs per foot OVER the excess tubing from the unit factory charge. Factory charge WILL be different from manufacturer to manufacturer. Some charge for 15 foot while others charge for 20 foot and others may even charge for 25 foot. That you will need to know. Subtract the extra tubing length from the factory length listed on the equipment. Multiply the extra length times .6 to get adjusted charge for tubing size. ie: 25 foot times .6 ozs equals 15.0 ozs. Divide this by 16, which is the number of ounces in a pound and you will get the amount needed to compensate for extra tubing. 150 ozs divided by 16 equals .94 pounds. As you monitor superheat or subcooling, slowly add the adjusted amount until the system is fully charged. Thats it. Very simple.

 

You forgot to add for the vapor line.

 

this has been fun!