Diagnostic Help - Old R-12 Walk-in Cooler

[David40]

Just wanted to get some opinions on diagnosing an old R-12 Walk-in cooler running 416a. Not pulling down the temp to an acceptable level.

Here are the operating parameters available to work with.
- System is air defrost only, TXV metering.
- Condenser (steel fins) and Evap are unobstructed, air flow looks good.
- Liq pressure 175lb, Saturation temp 130 degrees, Liq line temp 148 degrees. (Yikes Hot! -18 sub-cooling???)
- Suct line Pressure 20, Saturation temp 30 degrees, Suct line temp 59 degrees
- Condenser Ambient 90 degrees, outlet temp 110 degrees, = 20 degrees heat rise

What's your guess as to what is ailing this system? ( besides being obsolete )
How would you proceed?

Would love to hear the suggestions/ideas/opinions from the community.
Thanks

[Tayters]

Are you sure the condenor is clean. Have you blown it through with ofn?

Cheers,
Andy.

[David40]

Not sure I know what ofn is, but I did blow it out with some compressed CO2 and then washed it out real good with a hose and a spray nozzle. I would have used my coil cleaner I use on Aluminum coils but since this has steel fins there was no point cause there would be no foam action without the aluminum to react with. But it seems clear I can easily see through it. Anything specific you can recommend to clean steel fins.

[monkey spanners]

How can the liquid line temp be warmer than the condensing temp?

What temperature was the room at? Guessing around 52f?

How good is the insulation and door seals?
How well does the compressor pump?
Where did you measure the suction superheat? Is the line insulated?

[David40]

My thought exactly, how can that be?
Yeah I think the box was around 45 at the time. They assure me nothing has changed, door looks good, insulation is the same, but of course this box is outside and it's been real hot, still it was just as hot last year and it worked fine then.
Pump seems to pull down fine, but I'm going to redo that test and see if it will pull all the way to 15" vac just to be sure it's tight.
Superheat was measured about 6' from the Evap Outlet and looks to be around 29.

[nike123]

Superheat was measured about 6' from the TXV and looks to be around 29.

You mean 6' from the evaporator outlet?

[nike123]

(Yikes Hot! -18 sub-cooling???)

There is no such thing as positive subcooling or negative superheat!
If liquid line temperature and condensation pressure measurements are correct, you don't have condensation process at all in condenser, or composition of refrigerant blend is drastically changed from factory one.
Did you checked saturation pressure and temperature relation in refrigerant cylinder prior to charging refrigerant?
Did you charged exclusively liquid from cylinder?
Vacuum is measured these days with electronic micrometer, not with regular refrigerant gauge, or at least with vacuum meter of 100 or 1000 mBar scale. Good end vacuum is 0,02 in Hg (0,66 mBar). Too wet is 2,66 mbar or 0,079 in Hg. How can you see that difference on regular gauge?
To visibly change position of needle on regular refrigeration gage you could wait whole year and still have a leak.

[David40]

Yes, sorry Typo

[David40]

There is no such thing as positive subcooling or negative superheat!
If liquid line temperature and condensation pressure measurements are correct, you don't have condensation process at all in condenser, or composition of refrigerant blend is drastically changed from factory one.
Did you checked saturation pressure and temperature relation in refrigerant cylinder prior to charging refrigerant?
Did you charged exclusively liquid from cylinder?
Vacuum is measured these days with electronic micrometer, not with regular refrigerant gauge, or at least with vacuum meter of 100 or 1000 mBar scale. Good end vacuum is 0,02 in Hg (0,66 mBar). Too wet is 2,66 mbar or 0,079 in Hg. How can you see that difference on regular gauge?
To visibly change position of needle on regular refrigeration gage you could wait whole year and still have a leak.

I've never worked on this system before so I don't know who charged it. It crossed my mind that there could be non-condensables or something strange going on with composition, does 416a have a shelf life? I suppose I could try to just replace the refrigerant to see if that has any effect. It's an expensive experiment.

[nike123]

It is possible to check for the presence of NCGs in the condenser:
isolate refrigerant in the condenser, take the compressor offline, and run the condenser fan. When the refrigerant in the coil has come to air temperature, measure the air temperature and the pressure of the refrigerant inside the condenser. If the measured pressure matches up with the pressure indicated on a pressure/temperature chart, then there are no NCGs in the coil. If the pressure is more than a few psi higher than the chart, then NCGs are probably to blame.

Same is for wrong composition of gases in blend.
Are you sure in your liquid line temperature measurement?

[The MG Pony]

I would say it is a gas issue based off discription, gross over charge, or fractionalized gas, one thing to do to rule out a great many things is recover the charge, put the system on a vac, run the test nike laid out by leting the refrigerent stand to balance out temp with the air and to do a p/t chart test. Then recharge system via sub cooling, verify super heat once at set point temps. then show the guy how much you have left in the bottle! (Providing it was indeed an over charge was the culprit!)

surest way to eliminate a good chunk of issues. when ever code allows I use HC's for R-12 systems, superior resualts.

[David40]

Those are excellent ideas, I'm going to give that a try tomorrow.
Thanks much

[saintmichael36]

Low subcooling and high superheat = low charge. Find the leak, repair it, and charge the system to 10 deg F. subcooling .

[nike123]

Not likely with condenser approach of 38°F.

[David40]

Well here is the update of information I gathered today:
I did more testing. Sure enough the gas was compromised somehow, it was 15 degrees off what it should be at ambient so I did a vac and filled with fresh 416a. Condenser specified 65.1 oz of R-12 (4lb)so I filled with 3.5 lb 416a. Replacing the refrigerant dropped my LL temp down considerably but still does not explain why the temperature rises 6 degrees between the coil outlet and the receiver outlet. I verified the condenser coil is all steel fins and tubing, fins look a bit rusted/oxidized. All pipe readings with Fieldpiece clamp on probe.
With the box at 45 degrees LL pressure is 170 psi. Temp at the compressor discharge was 158 degrees, Temp at the condenser outlet pipe 109 degrees, LL out of the receiver rises to 115 degrees and drops to about 113 degrees where it enters the box. LL Sight Glass 6' away from the condenser is clear liq. no bubbles.
Suction Line temp is 65 degrees at the compressor and 58 degrees at the outlet of the evap. Suction Line pressure at the compressor is 21 psi.
Using the above numbers it would appear I now have a Superheat of 25 and Subcooling of 13?
Distance between the box and the condenser is about 15'.
Outdoor condenser and box. No head pressure control. Air defrost only via a "Little Gray Box" timer that takes the compressor off line for one hour each day.
Condenser Tecumseh AJB7465AXDXE
Evap Heatcraft ADT070AJ
I just gave them a call this evening and they tell me the box is still only pulled down to 42. (assuming their themometer is accurate)

[nike123]

Did you checked refrigerant in bottle to PT chart? Changed oil to POE?
After retrofiring to new refrigerant you should now try to adjust superheat at TXV. Record readings and turn TXV adjustment screw 1 turn counterclockwise to decrease superheat and wait 15 min to system stabilize and record new readings. Superheat should be adjusted to about 65% of evaporator TD.
Check bulb position and insulate it.Than check subcooling again to about 5-7K.

[mikeref]

My thought exactly, how can that be?
Yeah I think the box was around 45 at the time. They assure me nothing has changed, door looks good, insulation is the same, but of course this box is outside and it's been real hot, still it was just as hot last year and it worked fine then.
Pump seems to pull down fine, but I'm going to redo that test and see if it will pull all the way to 15" vac just to be sure it's tight.
Superheat was measured about 6' from the Evap Outlet and looks to be around 29.

Just going to run with a basic outline as this is an old system running without it's designed refrigerant.
15 inch vac is not good enough with a head pressure.
I'd expect somewhat better in an old compressor, like 25"+ and holding when compressor is off.(Piston compressors, and 10 Minutes monitoring vacc gauge.)
The compressor is not the only area to look into as external factors, such as heat load and changes in efficiency with the new refrigerant.
Older TX valves sometimes "squeeze" when duty is required, as in taking their sweet time to regulate and starve the evap coil for some time during regular cycles.

Efficiency of old steel evaps diminishes with age. Could this be an ongoing deterioration of the existing equipment that seemed to work OK in every other season except Summer..(Yeah i know, SST should show up as a problem. It might not if your valve does what i said above.)

To be honest, 170 or so PSI at your current ambient temps tells me the kit isn't working as hard as it could.
One hour "Defrost cycles."
Are you having ice-up on all, or part of the evaporator? One hour is too long in Summer.

[mikeref]

Use a data logger over a 24/ 48 hour period. Set it to 2 minutes.

[David40]

Aside from the condenser coil not transfering heat as it should I get the feeling that the TXV is holding open more than it should. Closing it down more would raise the high side, drop the low side, which would increase the work being done. This may be more that out of adjustment, it could be the TXV is failing. I have not noticed any icing or frost on the evap.
Yes, Refrigerant in bottle was spot on with the chart. No need for an oil change 416a is a drop in gas for an R-12 system.
I'll explore further.

[nike123]

http://www.airgasrefrigerants.com/pd...%20Guide-1.pdf

[1mikeefc1]

Had a similar problem on a cellar, was labelled r22 but had actually been changed to r224d, someone topped with r22 and cond pressure and temp went through the roof. Ended up dropping gas and blowing through system with nitro so it could be recharged on r 22 from fresh.

[THE DUDE]

You may want to check temp at the outlet of the TXV and make sure that it relates to your approximate pressure. You may have a Fractionated charge. Also the Superheat seems high. Good luck.

[nike123]

Closing it down more would raise the high side, drop the low side, which would increase the work being done.

I am not sugesting you to close TXV down. Contrary, open it to lower superheat.