R22/10 ton A/C Split... Suction pressure 30psi, suction line temp 16 Deg. Unit looked to be flooding back, i had no super heat out of the evaporator. Air flow is correct. I know that because circuit 2 runs perfect the evaporator coil is all interlaced w/circuit 1. Knowing all this information i elected to replace the txv after making adjustments to the original had no effect. The new TXV failed to correct the problem. ...we did finally find it had 3 of 4 distributor tubes plugged w/silver solder from the factory. How or why would a restriction look this way?
Head pressure = 275psi unit had fan cycling
yep.. i understand having low back,pressure, i just cant understand why the unit was flooding back to the compressor.
Thank you, that is a grate pointer! i wonder if i had done that would i have had the high super heat... then pointing to a restriction
You say its flooding back due to the fact that you had no superheat? If you understand as you say then you know with that big of a pressure drop due to the restriction and a low pressure in the evap your not absorbing any heat to "superheat" your refrigerant. when your not evaporating you prolly not condensing either, Which is why i asked for the head pressure and which is why it is good practice to jump that out and see whats going on.
The metering device is already the biggest pressure drop in a system, So the clogged up distributors will make this even worse
Couple of small questions. Did you replace the filter drier? What brand and age is this unit? How long is the run?
If you didn't do it right the first time it probably makes sense that your here asking the right way to do it now
Couple of small questions. Did you replace the filter drier? What brand and age is this unit? How long is the run?
drier replaced yes. unit is on it second season. its a custom unit i cant remember the design company the compressor is feet from the evap and the condenser is remoted 15 ft away. it also uses hot gas. we found the distributor plugged.
Was the hot gas not feeding the entire time if you where running 30 back pressure?
Did you remember if you were feeding before or after the evap
Hot gas entered the evaporator at the distributor. We valved off hot gas.
head pressure 275psi
suction pressure 30psi
suction line temp 16 degrees Fahrenheit
looked like flooding to me, i did not bypass head pressure control it has a 70 pound receiver and was 1/2 full. we found 3 of the 4 distributors plugged
Seems to me that if you had 75% of the evaporator shut down from the solder that the other 25% would have trouble absorbing the heat required to boil even the least amount of refrigerant going through the TXV.
MIke
10 ton system with 4 distribitor tubes - I find it is odd ? Did not say it is wrong
Circuit #1 and #2 -- are they tied together as one common suction line out of the coil ?
30 PSIG and 16 degree suction line temp -- that gives you 9 degrees super heat and not at NO SUPER HEAT
10 ton system with 4 distributor tubes - I find it is odd ? Did not say it is wrong
Circuit #1 and #2 -- are they tied together as one common suction line out of the coil ?
30 PSIG and 16 degree suction line temp -- that gives you 9 degrees super heat and not at NO SUPER HEAT
I can get the sporlyn part number on the distributor.
my TP chart at the time i measured this units superheat was zero. i am not looking at a chart now but i think 30psi R22 = 16-18 degrees F
This unit has two compressor circuits and condenser circuits no common piping. i would like to clear my confusion and understand what can cause this symptom.
Your super heat was 9 degrees, the TXV was doing its job.
This is pertty much the correct answer.
You have a two circuit, 10 ton machine, probably 5 tons each.
The 75% of the distributors were clogged AFTER the txv. All five tons were going through only 25% of the evap coil, not allowing it to boil off properly, and keeping it a saturated mixture.
The resulting 9 degree superheat is a resulting mix temperature of the clogged passes and the good pass.
0 degree superheat could have been measured depending on where your sensor was located (possibly near active section outlet)
If it's a Sporlan, check the distributor nozzle size if you change the TEV. and make sure it's correct per your Sporlan rep.
In my experience, the second stage circuit of an intertwined evaporator has less of a load on it than the first circuit.
BTW, if you have hot gas bypass, ALL distributor feeder tubes should be sized one size larger than without hot gas.
jogas
Use this PT chart: http://sporlan.jandrewschoen.com/Form1.pdf
The solution here is fairly simple. You only had 25 percent of your evaporator working. This caused a mismatch between your evaporator and compressor capacities which resulted in the circuit operating at well below design suction pressures.
The key to finding this type of problem is to first confirm proper airflow, which you did. Second, if the TEV is controlling superheat properly, then something is likely odd with the evaporator coil.
You can check for plugged circuits by simply measuring the circuit temperatures as they enter the suction header. If these temperatures are holding rock steady at the same temperature as your return air, you likely have a problem. If temperatures show some fluctuation and are below return air temperature, you know refrigerant is entering the circuit.
Last edited by Andy Schoen; 06-19-2008 at 08:54 PM.
Depending on your chart and whether it breaks down per degree or in even pound increments, or some of them go by 2 degrees, you get 30 psi boiling point of 7 deg. (or one of my charts shows 29.1 psi at 6 deg. and 30.9 psi at 8 deg. ergo directly proportional extrapolation gives you 30 psi at 7 deg.). (however I never looked over the ranges on the chart and I'm wondering if I'm missing something from my high school chemistry pv=nrt stuff, because I would think that the boiling point would move proportionally with pressure, but as the temperature increases the boiling pressure difference in 2 deg. increments goes from 1.8 degrees in the range we're discussing here up to almost 6 psi change per 2 degree change near the high end of the temp chart. That's not exactly a logarithmic increase, but it is more than an arithmetic straight line, it's a curve, and I'm wondering what quantity in the equation is exponented or what am forgetting. for you theory guys)
And, for the bigger hammer more solder in us all, how did the three distribution tubes get blocked by solder? Not meaning to disparage the instalation of the new TEV necessarily because you said the symptoms were the same before and after the replacement, although one supposes it is possible that the TEV charge was low and then when you put a new one in but might have accidentally blocked a few distribution tubes that you got almost an identical situation. ironic isn't it. and or since this is only one year old, could it have been running like this all along and depending on the one working circuit?
As various other threads will attest, I was confused by a low load circumstance myself last week, thinking the TEV needed adjustment when likely most of the fan coils in the house I was working on were turned off.
Circumstances were similar but not identical. low suction (mine was 48 and temp was 27 deg so I only had a couple degrees of superheat -- not factoring water temps, i'm a little confused on exactly how you add those in -- but I still had a little. But I'm getting icing back because of the line temp, not necessarily because I'm carrying a great deal of liquid.
brian
It does with an ideal gas, and reasonably so with a real gas. But what we're looking at here is the pressure temperature relationship at a phase transition, i.e., saturated vapor/liquid. The ideal gas equation is not applicable.
The Clausius-Clapeyron equation, however, can be used to estimate the P-T relationship at saturation.
yep you guys have picked up on an error in my details. my suction pressures varied from 30psi-40psi and suction line temps also varied accordingly. i know the uni was flooding. I dont get it.