I hate to say this but.....
I have never really done a sub cooling in my life. Only in school.
I forgot now what your sub cooling should even be.
The first co I ever worked for we used superheat to charge. Now, I just go by the charging table on the unit. 95% of the units I work on are 5 years old or newer tempstars. On their charging chart, all they want is indoor wet and dry bulb temp, and outdoor drybulb temp.
I used to have a card telling me what superheat should be at different ambient temps. I really should get one again and start checking sub cooling.
I ran into one just today that had a 325 head and 70 suction. Cleaned the coil and all, still can't get that damn head pressure down.
Superheat / Subcooling
i just got out of school. i used to hook both sides up but i really dont see the need to . i have both on when charging of course but it seems like a waste of time. superheat doesnt care what liquid temp is! or pressure. but as for the freezing, i figure its low, BUT, BUT!!!!, i always check filters, blowers, coils and everything! if i find nothing there, i check charge. I find it works pretty darn good! [/QUOTE]
Checking the sub cooling is just as important as checking the superheat in my opinion. [/B][/QUOTE]
yeah. You need to check subcooling.
You wont BELIEVE how many systems I've thought people charged ONLY by superheat.
Sometimes there is a restriciton. And someone just thinks it is low on the gas. Adds a buttload to get the superheat down. Little do they know... 30+ degrees of subcooling is BAD!!!
anyway. Hook up the high side. I focus as much on subcooling and head pressure when i am charging as I do superheat. ESPECIALLY on a TXV. Subcool is ALL you care about or you could accidentally add way too much refer in that case as well. I see it ALL of the time, especially from guys who did PM in mild weather. [/B][/QUOTE]
I had a couple prior techs performing system startups and installs and they always reach for the green cans. Charged it 20 deg. above ambient on the high side guage. To date, I've recovered 45 lbs of r-22...I've found 17lbs in a 5 ton system, 15lbs in a 4 ton system, etc... Save the compressor and yourself, do a super heat or sub cooling.
Happiness is the only good. The time to be happy is now. The place to be happy is here. The way to be happy is to make others so.
-Robert Green Ingersoll
the way i do it is superheat for a cap tube or piston and subcooling on a txv. i'm pretty sure txv maintains a set superheat?
For the most part a TXV will maintain a set superheat. Usually 12 degrees F for a high temp system like residential and commercial comfort equipment. I've found a few that were off a bit and made some adjustments but, those were few and far between.
Cap tubes and piston systems have changing superheats from load changes.
TXV's do the same with their subcooling temperatures.
I have some charging slide charts I obtained from the CARRIER distributor I use some time ago and those things are invaluable!
Just take some temperature measurements as indicated on the slide chart, work the chart to get required superheat or subcooling and add or remove refrigerant to obtain the necessary readings. These charts are available for R-22 and R-410a and they work perfectly!
Two things are infinite: the universe and human stupidity; and Im not sure about the universe. Albert Einstein
i have a trane slide chart. it has the superheat calculator and a subcooling chart. for superheat, i get indoor temp and outdoor temp. that tells me the superheat and i slide the chart to the corresponding superheat. it says that at a certain lo side pressure, the suction line should be a certain temp. There is a + or - allowance of 5*F. Too hot, pump it up, too cold, blow it out!
Kinda the same thing for sub cooling. I just plot the hi side temp and pressure. Depending upon where the plot is, you pump it up or blow it out!
I dont mean litteraly blow n go by the way!