Non-condensibles?

Jeff Lawrence_24

To pump this one down, about 20-30% of the charge would have to go into a recovery drum before I could do a complete pump down. The evap is in the attic 25 feet up and about 30 feet over. That condenser wouldn't hold all the refrigerant.

Jeff Lawrence_24

The best way?

Professor,

I recently was called to service a new customers cooling system. Since this is a 2 story house with one system in the attic and the other in the crawlspace, I started in the attic.

As I usually do, I checked the air filter. I also removed the cover (Darn builders grade Lennox!) to check the blower wheel to see how dirty it was. I also removed the Evap coil cover and slid it out to get a look at the evap coil. Thankfully the blower and coil were clean. I turned on the cooling system and put my Fluke 52 in the attic while I went to get the new pleated filter.

My Fluke 52 is a dual probe digital thermometer with a pipe clamp on posit 1 (put on the suction line at the evap) and the bead probe (put in the ductwork) on posit 2. When I came back up, the air temps were dropping and everything looked good.

Or so I thought.

I know I've seen this before, but not recently. The Suction Line Temps (SLT) were moving around, both up and down. In about a 5 minute time period, the temps were moving from 41° to 67°! The Leaving Air temps (LAT) were following behind the SLT but swinging from 56° to 64°. (The temps were moving up AND down in the 5 minutes.)

I went outside to check the condenser and put my gauges and the digital thermometer on it. I don't exactly remember the readings because I was talking to the Home Owner and didn't write them down, but they were moving also.

From these readings, I guessed that there were non-condensibles in the system. I gave the Home Owner a price on recovering all the refrigerant, flushing everything with a nitrogen purge, installing suction and liquid line filters, evacuating it, and recharging with virgin refrigerant. I also know that I'll have to return and replace and/or remove the suction line drier. Since this is an about 10-12 year old system and I have no idea how long it's been contaminated, what are the chances that the oil has started to acidify?

The good thing was that the downstairs unit was rock solid after about a 5 minute run time.

Thanks Professor.

Empire_2

Hello Jeff;-)

If I may,... You have a good grasp on what it may be, but did not say what type of metering device you have. Assuming that it is a non-condensable problem, you are right that the pressures will fluctuate. If you have the ability to pump your system down, this will definitely let you know if you have non-condensables. As for acidity levels, I would add both dryers as you said, but test your acid levels as to the severity of the contamination level. May not require the change out of dryers as you stated. Although it is great practice to do, often times it is not required. Treat it as time and materials....Let the customer know that it is possible that more attention needs to be applied, but your acid test will tell you if it's necessary.

Good call by the way........... In my opinion nitrogen not be introduced to the system at further cost as if it were that bad, no flush could help without changing oil etc... A triple evacuation would be in order here and an "HH" series acid clean up suction line dryer would make things redundant and help the final out come.

Mike T.

D lux_2

can you pump unit down

run fan in OD unit ck pres.temp. chart to see if you might have non condenables.might have to install an extra LL valve . You might have a blocked txv or piston. I take it this is an Ac not a heatpump.

jim lockard

12 years old

I have to ask how much time and effort are you willing to commit to a repair V. replacment of the system. Jeff your in GA with a 5 to 6 month cooling season, top floor unit, Builders grade system. Most likly a blow and go evacuation, maybe just a green can purge?
TXV or flowcheck ? did you check the indoor coil for even loading? What was the delta T across the coil? Was your super heat in line? What was you return air temp? What was the outside air temp? What were the gauge readings at the condensor? Liquid pipe temp? (should always be higher then outside air temp)Is the return duct leak tight in the attic? Line set is kink free from condensor to A/H? Best Wishes J.Lockard

Techman

non-condensibles

Jeff,in order to determine if you have non-cond. in the system ,is to know what your head press is supposed to be ,for the given conditions, and compare that to the head press that you do have.If your hi side press is higher ,than you. proberly have non-cond in the system

Empire_2

Techman

True you can also tell by what you described, but why not eliminate all mechanical devices, like the compressor in case something else is wrong. I personally think pump down is the truest way to determine the non-condensables. T&P charts don't lie...;-)

Mike T.

Techman

non-condensibles

Jeff,ASSUMING that you do have non-cond, and possibly acids,caused by the non-c's,then you recover the R-22 anyway.[Typically I install my gages first and check the press/temp's vs. indoor and outdoor air temps}A lot of residential C.U. donot have the right type of "King Valve", A.K.A. the liquid line service valve.By shuting {front seating}the L.L.S.V. the C.U.will go into a "pump down",but your hi side hose is now connected to the liquid line ,it is not connected to the C.U.
O.K. Now , can you do the entire job from "truck stock"? or is this "I'll be back" situation? If this is a reschedual job,bring two recovery tanks.The first drum gets connected to the system IMMEDIATLY upon arrival,so as the drum sit's in the ICE BATH it is sucking the R-22 out of the system faster tnan any recovery pump.While this is taking place , I bring over all of driers ,torch , moisture indicator ,recovery pump ,extention cord,etc. etc. Then I use Tank #2 and Let the recovery pump the rest.
Oh ,by the way, I stop by ANY convience store and pick up a couple of bags of ice.It makes life a little easier.Most residential systems have no more than10-12 lbs of R-22.
On systems with the "wrong style" hi side service ,I also install a hand shut off valve in the liquid line so that a "pump down " can be performed and tested at the same time. Good Luck.