proper system charging

[bornriding]

I am asking for everyones technique on determining when a system has the proper amount of refrigerant.

for example: residential cooling unit found low on refrigerant. What do ya'll use as the determining
factor(s) when charging a system ???

I teach at a local tech school, and this is the semester for teaching the students how to properly charge a system.

weighing & measuring the manufacturers recommended amount of charge, of course
site glass, of course

but, if you have a system that is low, how do you (I have my method ) dtermine when you have the system correctly charged ??

[dash]

Look in the "For Your Interest" section ,on this site,you'll likely want to printout the infromation that you find.

[Shophound]

Originally posted by bornriding

but, if you have a system that is low, how do you (I have my method ) dtermine when you have the system correctly charged ??

Manufacturer's charging chart, if available. If not, superheat for piston metering device and subcooling for TXV systems.

Sight glasses are NOT a good charging tool. They are useful mainly for ensuring the metering device (especially a TXV) is receiving a solid column of liquid from the condenser. This is why a sight glass near the TXV is the best location.

Weighing the charge into an evacuated system is dynamite for unitary and package systems, and also good for split sysetms, but with splits, adjustments must be made for linesets over a certain length.

What you do NOT want to teach your students is to charge until the suction line is "beer can cold". All that amounts to is a good way to kill a compressor.

[btexpress]

By subcooling if the unit has a TXV. By superheat if the unit has a piston type metering device.
P.S. I wouldn't trust a sightglass, especially if a liq line filter/drier (possibly plugged or restricted) is upstream of it. JMHO
Thanks Bald Loonie, I really should proofread my post...

[Edited by btexpress on 02-08-2005 at 02:32 PM]

[BaldLoonie]

bt, me thinks you got it backwards. Check your typing again!

[docholiday]

I'm glad to see others despise the use of sight glasses in applications where virtually any level of techncian can be assigned to work. All to often the tech cranks open the jug and overcharges it to clear the sight glass.

[roosterman]

we'll im from south TX rio gradne valley,this work's for me
hi-side: ambient temp plus (+) 30-35 deg,go to temp-psi chart[r-22]that should be correct hi-side,if higher?then a visual on condenser shape,cleanleness,fan speed,coil deterioration,weed's,or ??? groosley over charge?? then there is the data plate F.L.A[full load amp's]on compressor

low-side :central a/c,im looking for about a 15deg split [return take-away(-)suppy air temp[DEG]==T.D.
ALSO I'm looking for a 40deg [evap temp]which is about
[+/-]68.5,69,70 psi on the gauge*****note checking for coil cleanlenees,fan[indoor blower wheel]cleanleness[fin's colect lots of dirt and can add wiehgt to motor,causeing it to over heat and slow down]thuse slowing air flow acros evap coil[can cuase,frosting]

this wat has worked for me i should check for super heat,the way to check is usuelly inside the contactor area cover [but i have not done that most of the time ,in SOUTH TX]this has worked fine for me for central a/c

[billva]

willie,
you need to catch up on some things.

if this is your career, have you considered continuing ed. classes? i mean, hey, no one can ever know too much, right?

your methods of charging a/c's and sizing furnaces went out 30 yrs. ago.

spend some time on this board and you will find you learn something new every day. which in turn will make you a far better tech than your co-workers and/or competition.

check out the "for you interest" section, there is an unbelievable wealth of info there. good luck.

[Wild Leg]

Originally posted by williesanchez69
we'll im from south TX rio gradne valley,this work's for me
hi-side: ambient temp plus (+) 30-35 deg,go to temp-psi chart[r-22]that should be correct hi-side,if higher?then a visual on condenser shape,cleanleness,fan speed,coil deterioration,weed's,or ??? groosley over charge?? then there is the data plate F.L.A[full load amp's]on compressor

low-side :central a/c,im looking for about a 15deg split [return take-away(-)suppy air temp[DEG]==T.D.
ALSO I'm looking for a 40deg [evap temp]which is about
[+/-]68.5,69,70 psi on the gauge*****note checking for coil cleanlenees,fan[indoor blower wheel]cleanleness[fin's colect lots of dirt and can add wiehgt to motor,causeing it to over heat and slow down]thuse slowing air flow acros evap coil[can cuase,frosting]

this wat has worked for me i should check for super heat,the way to check is usuelly inside the contactor area cover [but i have not done that most of the time ,in SOUTH TX]this has worked fine for me for central a/c

This is absolute proof that air conditioners are bulletproof.

The 30+ rule is more than a little outdated.
Also the 40 degree evaporator.

What you are doing is not much better than guesswork.

Buy some books.

Read 'em.

Take some classes.

Smart pays more.

Good luck.

[btexpress]

Willie,
Billva and Bwal2 have given you some good advice. If you want to continue in this business with the new technology (i.e. v.s. blowers, two stage comps, etc, etc). I would truly take their advice. Good Luck

[beenthere]

Hey, we take care of some old clunkers that i still use beer can cold methold on.

I'm afraid they'll die if I change charge methold on them.

Wille, the higher seer units aren't going to have the same high head of the old units, and the compressors won't last as long running if their over charged.

Time to go back to the books, so you don't get too over loaded with calls.

I check the ID wet bulb when i go in and check the t stat, then my OD dry bulb while I'm at the unit, it only takes a few minutes to do and then you know what your super heat should be.

And of course if its a txv, then subcool.

I was taught the same way you were taught.

[filterchanger]

if i understood willie correctly he said outdoor ambient + 30 for head preasure, if this is correct on a 90 degree day you are looking for a 120 head preasure, willie i think if you wanted you could learn to calculate superheat and subcooling in about 10 min,really there is no excuse for doing it any other way

[beenthere]

Originally posted by filterchanger
if i understood willie correctly he said outdoor ambient + 30 for head preasure, if this is correct on a 90 degree day you are looking for a 120 head preasure, willie i think if you wanted you could learn to calculate superheat and subcooling in about 10 min,really there is no excuse for doing it any other way

No, on a 90 degree day, he looks for a 120 degree saturated guage temp, not pressure.

[filterchanger]

thanks been there,,then thats the way ill do it for now on

[beenthere]

Originally posted by filterchanger
thanks been there,,then thats the way ill do it for now on

LOL... Thats the method he uses. Saturation 30 to 35 degrees above outdoor temp.
Worked ok on the older units.(The 70s.)

[bornriding]

I appreciate ya'lls input

but, why did no one mention the delta 't' across the air handler

I am waiting to be torn apart for this, but.......

I use a 20 degree delta 't' with humidity between 40 & 60 %
( return air ) if humidity is above or below, I adjust the delta 't' slightly.

also I have found, that ,if my ductwork is correct, and my
blower speed in decent, then my suction line temp will be within 3-4 degrees of my supply air temp, when my system is correctly charged

ok ! hit me with it .... I can take it

also, I have found that superheat & subcooling only work if you take the measurements right before the system shuts off ???

[Advanced Response]

Born,,

You definately need some system charging classes...

Do some checking on this site.. This has been talked about many times..

It is important to take deltaT's, low side pressure, high side pressure, liquid line temp, suction line temp, and compressor amp checks on every unit you service and install.. As when all the data is collected it will tell you many thing that may or may not be operating properly..

For a piston system.. Proper charging..Superheat most important!
Take a wet bulb temp at the main return air grille or in return air duct..Take a deltaT across the indoor coil.. Take outdoor temp by the outdoor coil(not in direct sunlight)... Take a suction and liquid line pressure reading... Take a suction line temp 6-8inches from compressor or near the pump down valve and take a liquid line temp... Subtract boiling temp of the suction pressure from the suction line temp for the current superheat reading... This should line up to the superheat slide chart that takes into account the indoor wet bulb and out door temperature.... Note.. The indoor and outdoor coil must be clean and blower must be moving the required air before superheat is properly set...DUH!!
Now remember you took all reading on the system because to get a overall picture what the whole system is doing to make appropriate repairs..DUH!!

For a TXV... Proper charging.... Subcool is the most important.. You should know this and I am tired of typing..
Look it up in for your interest section..

As I stated it is most important for you to set the superheat on a piston metered system and subcool on a TXV system but that does not mean that you don't need to take other reading to get an overall picture of the internal operation of the freon..

Goodluck
J

Please change your ways and become a true pro.. We need to better this industry in the eye of the public by using factory guidelines and proper technique..

[bornriding]

Advanced,you
did not give me any idea on what superheat to set for or what subcooling to set for ???????
no one seems to know or you only have a range of super or sub ?
Don't mean to insult or be argumentive, but, in my experience, I find superheat & subcooling to vary too much
to use as a 'definite'

[Advanced Response]

Born,
Piston metering system:
Superheat is variable depending upon the outdoor temp and indoor wetbulb!! That is why I stated that you take the outdoor temp by the outdoor coil and an indoor wetbulb near the return.. Most manufacturer use a slide chart for piston units,,, very simple you look at the chart and line up the outdoor temp and the indoor wetbulb temp on the slide chart and it will give you the superheat(usually allowed (+-)5degrees of that number)... Example:
75 degrees outdoor temp
62 degrees wetbulb temp
on bryant charging chart will give you 15degrees superheat needed +-5degrees...
Example 2:
90 degrees outdoor temp
62 degrees wetbulb temp
on bryant charging chart will give you 5degrees superheat needed +-5degrees..
Example 3(a system that has been down for a while):
90 degrees outdoor temp
76 degrees wetbulb temp(very humid in house)
on bryant charging chart will give you 31degrees superheat needed +-5degrees..
As you can see superheat does vary widely on a system depending on the conditions that the system is operating in..
If a Bryant piston system is properly charged in the first example,, all other situations will properly line up on the chart when those operating parameters happen..

As far as subcool goes,, Most manufactures give you the subcool number on the outdoor unit(i.e. bryant/carrier).. or they give you a graph chart to use based on that number(i.e. Trane) but the chart is based off of the fixed subcool number.. I remember a Bryant 12seer unit that had a 13degrees subcool required and a bryant 11seer that had a 11degress subcool required.. Most subcool readings allow for a +-3degrees of the required reading..

There is a proper way to charge or check a units charge.. To do this properly all techs should calibrate their gages and temperature probes regularly.. Also it is very important to make sure your temperature probe is secured well to the line and well insulated out of direct sunlight..
As long as proper technique and charts are used you will have a properly charged unit..

Please get some training from a supply house on proper charging.. This field is full of hacks,, we need more true professionals!!! From your comments it seems like you want to be a true pro but just don't know any better.. Time to put aside the ignorance and get educated..

Step up to the education plate...
Good day
J
This is my last post on this subject,, if you truely want to do it the correct way, you can research this subject on this site for more information and seak a proper charging technique class from your local supply house..

P.S. If you want addition contribution to this subject by other members, Please post it in the pro's forum as this is our trade and a diyer does not need to see these posts and try to charge their own unit..

[Edited by Advanced Response on 02-10-2005 at 12:10 PM]

[docholiday]

I cant believe what I am reading here today.

There is no quick charing method. Superheat and subcooling are not variable, there is no room for negotiation.

You want a temperature split that works in every case but you're not willing to accept the fact that the latent load is not a sensible temperature. Sorry to say, your split is usless in the charging procedure.

30 over ambient has long since been a thing of the past if ever it was true.

If you want to charge a unit proper you need to take the time to do it right.

Turn the system on and before you even think about hooking gauges up you need to verify several things.
1. Matched equipment (otherwise the charts are worthless) This also included proper sizing technciques.
2. Verify airflow, it needs to be within 10% or less of nominal or the charts are worthless.
3. Clean system. You cannot use a dirty system (coils, filters, blowers etc) and expect to be right.
4. Season. Your methods for charging are different for cooling then they are for heating. For this free tip we'll discuss cooling.
5. Indoor return temperature, you need to know the DB and WB as it enters the coil, not the space temperature in the home.
6. Outdoor ambient temperature, this is the temperature of the air passing through the outdoor coil, not the temperature at the bank up the street.
7. Calibrated and accurate tools. If you suggest you use a laser guided infared temperature probe, this conversation is over. Gauges should be calibrated regularly.
8. Determine whether you are dealing with a fixed oriface or TXV as a metering device. For this example we'll use a TXV.
9. Line length, size and vertical speration. Exceeding or failing to meet the requirements will result in unfavorable performance.

Now you can attach your gauges. The system has to run for a minimum of 15 minutes before you do anything. You also ned to read and document some oeprational temperatures.
1. Liquid line temperature at service valve
2. LL temp leaving outdoor coil manifold.
2. Suction Line temperature at service valve
3. LL temp at indoor coil
4. SL temp at indoor coil
5. Saturation temperature of suction
6. Saturation temperature of liquid
7. Discharge temperature.

Based on your readings above, (note, pressures are irrelevent), you can examine the charging chart and determine the proper subcooling level. Some mfg's offer pressures based on temperatures in their charts to allow for shall we say ignorant (and I say that in the nicest way) technicians.

For arguments sake lets say the chart dictates a 10 degree subcooling requirement. You still need to figure out the superheat to veryify TXV operation. Now you can add or remove refirgerant according to the subcooling chart. after adding or removing a little, you need to allow time for the system to operate and equilibrate as much as 15 minutes. Recheck and readjust again. Wait again. Once you are at the proper subcooling level, all readings need to be reverified and documented. Just because a reading such as indoor LL temperature is not used in the charging chart doesnt mean you can avoid reading it, it tells you whether there is indeed an issue that needs to be dealt with prior to charging.

The techncian can, with this information "see" into the system to determine and verify optimum performance and efficiency

You tell me, are you worth your wages to use a rule of thumb? Frankly, we could train monkeys to do non-technical charging if it worked and they work for much less than most techncians are willing to work for plus they dont need healthcare policies.

Edit: Advance you are right about the training... Apparently you answered while I was typing my response.







[Edited by docholiday on 02-10-2005 at 12:23 PM]