Mystery problem?

[drifter43]

I know that some one can help me with this.

WIC with 2 Evap,s = LLE136BJ & LLE170BJ with a roof mounted COPELAND 5HP R-22 condensing unit with a head master and reciver and electric defrost (Wallgeens set-up) sorry no # for the condensing unit.

Found rt evap with heavy clear ice @ bottom 1/2 that i defrosted,fairly well. Also i had to push back the defrost heater in this area as well as the lt evap at the top but it only had light frost. Sight glass was flashing every 2 min or so and we had replaced the compr back in jan so i added aprox, 20lbs of r-22 with little change. sight glass is clear now.

Box @ 45.
AMB 95
PSI 35-40 / 240-250
S.H. @ COMP, 25-27.
S.C. @ COMP, 7-8.
TD @ LT EVAP 6. with frost at top 2 passes balance of passes sweating.
TD @ RT EVAP 3. with passes on inside near fans frosting and bottom passes frosting, balance of passes sweating.

What do you think, oil loged evaps? or 2 starving TXV,s or what. thanks for input.

[R12rules]

You are one of the first to provide us with GREAT initial info on the system you are asking a question about.

However ... you failed to fill us in, so to speak, as to what your gut feelings are about the starving evaps!

You asked if we think they are starving.


WELL DUH!!!

Stop the fans and look at your frost pattern and you'll see with your own eyes what the frost pattern is!

Also, use your temp probe to see what your TD is across the coils.

That compressor, in a walk in cooler, is just right for that pair of evaps .... depending upon which TX valves you have operating in there.
Unless they are balanced port valves, they should be rated at 1 1/2 ton a piece.
Circle K used a lot of these systems in their California stores.


Since both coils are showing simular patterns ... you might want to lok into what your filter/ drier is doing.


Hope this helps. There is nothing like being there, on site, to diagnose a problem.

[drifter43]

well im not sure what this thing is doing, because of the 2 different frost patterns on each evap, and i never had problems with oil loged evap, thought it may be that? also i did list the TD for each evap,.


Thanks for your reply.

[stormrider]

It is a funny thing that some check superheat at the compressor with a remote unit. There are too many things that could affect the temp at the compressor.

Check the superheat at the TXV sensing bulb, you maybe suprised.

It has been in my experience that a 250#, if the condenser is clean, head with a medium temp R-22 is too high. From what you had told me you have a TXV that is malfuntioning. Do you home work before you change anything. Check the BTU rating of the compressor and check the BTU rating of the evaps. Then, change BOTH txv's with the correct TXV.

Oil logged? Possibly, but the new compressor should have pulled any oil from the evaps that the old comp pumped out. So, check your sight glass for an over charge of oil. If so, change your oil.

Good luck

[gerryboy00]

Originally posted by drifter43
Snake got into your evap, watch out there atracted to freon. LOL.





could it be your problem....?

[Dad]

drifter43

Forum Rules (http://hvac-talk.com/vbb/showthread.php?threadid=1241)

One subject, One post. Please follow the site rules.

Thank you.

[icemeister]

The clear ice buildup on the bottom of the RH evaporator tells me that this coil has not been completely defrosting for a long time.....possibly months. It troubles me that you say you got it "fairly well defrosted". That's not good enough. That clear ice can totally block a coil that "appears" clean......you can't see it. Also if there's ice left on the coil it will continue to build up again.

While medium temp with electric defrost isn't common for me except in 28ºF meat coolers, the fact that you have heated defrost should in itself guarantee a clear coil, so I would first check the defrost heaters and controls. For those Calrod heater elements that pop out there are clip available for holding them in or you can fashion your own with some wire.

The fact that you had to add twenty pounds of juice to clear up the sightglass on a 5 HP system tells me you were way low on charge. Most systems of that size don't hold much more than that altogether. A long run time on a low charge like could easily cause that iceberg you found.

Get everything thawed out completely and then make sure you have a clear sightglass. Then check your expansion valves and thermostatic elements (powerheads). From my rough calculations the smaller coil should have a 1 1/2 ton valve and the larger coil a 2 ton valve. The charge on the element should be a VC. Check and clean the TXV inlet screens while you're at it.

Check your superheat at each evaporator outlet and initially shoot for around 10ºF. The coil's distributor nozzle size issue can show up here as an uneven frost pattern on the coils. You may have to check the nozzle sizing for this application as others have suggested elsewhere.

I really don't see an oil logging problem happening here....not with R22 at these temperatures.

[drifter43]

As hard as i try im stil not perfect at this ocupation, dont think any one is but we all keep on keeping on.

Thanks for all your replys.

[LGM]

For some reason my previous post was erased. So, I'll try again.

The evaporators you have are Bohn LOW TEMP evaps. They come with both low temp and medium temp nozzles. What your describing is a result of having the low temp nozzle in a medium temp application.

What happens is the low temp nozzle is oversized in the medium temp application and causes UNEVEN distribution of refrigerant in the evaporator. Some circuits will freeze and some will only sweat.

If you call Bohn at 800-321-1881 and ask for technical service they can help you resize the nozzle and save you a lot of unnecessary work.

[Dad]

Originally posted by LGM
For some reason my previous post was erased. So, I'll try again.



Thank you LGM

Your previous post was not erased. It was in one of the other illegal two threads of the same discussion. This is against the rules to post multiple threads for the same discussion.

Thanks for your repost here on the original thread.

[LGM]

Ooops!

[drifter43]

Sorry for the multible listings, I did not know about the rule.

Thanks for the replys, "LGM this may be the problem!" all though this was the first time I looked at this problem our Co. has lots of past history with it and has never been resolved. Also I normaly do SH check at the evap, but they never installed any low side ports there. I will be returning and installing them and trying to adjust SH but will check into the wrong nozzle thing, or any other problems like pluged inlet screens as icemeister sugested. Oh I also found out that another tech, had replaced both of the TXV,s because of this some time last year, and no results.


Thanks all.

[Edited by drifter43 on 08-05-2005 at 10:08 PM]

[LGM]

One sure way to find this is to take SH readings on all of the tubes exiting the coil and going into the suction header. You will find they are not the same. If I remember correctly, you should have a maximum of 2 to 3 degrees difference between any of the tubes.

Let us know the outcome.