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.