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icetec9
26-09-2006, 04:02 AM
Im working on a walk-in cooler.
I found unit with 2 of the 3 evaps with a lot of ice on the bottom half of the coil,coming out 5in thick. The third coil is not froze at all. This is a R22 system.I let the unit thaw.
I found the unit has pressures at 190/36psig.
With a full sight glass. This is a new system of about 8 months. Super heat on all coils are high.The first 2 coils have an uneven frost pattern. With the third with an even pattern. The first 2 coils have a temp diff across the coil of about 12+, the third coil had almost no td at all.

I cheaked all the normal problems like txv screens, they were clear. Adjusting the txvs were not changing the super heat. TXVs are wide open. Pressures are too low by far, still 190/36-38,, and outside air temp of 80degrees *F.

Ok unit is not building up any head pressure,the headmaster is not by-passing. I found the liquid line was a 3\8 line feeding three coils.I was worried the the txv's were not getting full liquid. To be sure i changed the liquid line to 1/2 in,and installed sightglasses before each txv. Each coil is getting full liqid to the coil.But there was no change.

I cheaked each coil for the proper orfice in the destributors. The manifacture said it should be a size 3/4. These are three 11000 btu coils. Copland comp in system CRN5-0500-TFS. All three txvs are Sporlan SBFV-A-C balance port valves. witch are 3/4 to 1 1/2 ton valve.

The cond unit has a 25lb recever and there is 25 lb ref in the system i could only get the head pressure up by cycling the cond fan.
Soo it still has a low head press and low suction press. Manufacture reports that the unit in sized properly. The manufacture said he couldnt help me anymore then that.
Im thinking the condensing unit is over sized and /or the condenser coil is over sized.

what do you think ?
howcan i correct this problem?
still have no td on coil #3.head press to low?

thanks for your advice.

Samarjit Sen
26-09-2006, 06:46 AM
From the details provided by you, it appears that your operating one refrigeration compressor and a common liquid line to all the three Evaporators. To be able to assist you, could you kindly let me know the following.

1. The size of the condenser, ie the finned area, row deep, no. of feeds, subcooling feeds and finned spacing.

2. The pipe sizing ie, the size of the main liquid line, the branch liquid line to the individual Evaporators, and a sketch of the liquid line and suction line as laid out by you. Other wise you may describe the layout such as how have you laid it, if there is a liquid line header and a suction line header.

I have a feeling that the problem is in the pipe line. With maybe some small changes which I can suggest only after I get the above details , your plant should operate perfectly.

I have designed and installed a large number of Cold Rooms with similar systems and had faced similar problems initially. Now I do not make these mistakes.

With best wishes,

monkey spanners
27-09-2006, 05:37 PM
Hi Icetech9
The nearest (in the uk) copeland condsing unit i could find details on has a CRNQ-500 compressor which is rated at 8.4/9.9 Kw depending on the condenser size which work out as 28000/34000 Btu at 73.4 F (-5 C) evaporating and 90 F (32 C) condensing tempeature. So it sounds like its in the ball park with your three evaporators giving 33000 Btu. All the chiller evaporators are rated at -8 c (63 F) in my catalogue.
What is the temperature range of the expansion valves e.g. 50F/ -10F, 0F/ -40F or are they MOP vavles? If braze in, have they been "cooked". Are you sure it is charged with R22 as per spec, I once worked with a guy who used to say things like " at that time of night any gas will do":eek::eek::eek: and " you'll be surprised at what you can get away with":eek: i always wonder what the previous engineer has done.
Are the expansion valve phials mounted correctly, not on the common suction line, should be exterally equalised if used with distributors. equalising line not full of solder were its brazed to the suction line or schraeder valve left in connection with no depressor in the capiliary? Are the txv's R22 and not R404a/R134a etc.
Are the txv phials mounted away from any ice formation as i have seen on a water chiller where ice has formed on the evaporator inlet pipe and grown big enough to cover the phial on the evaporator outlet causing the valve to shut down.
I think i'd try some new txv's, or a least one on the third evaporator.

Cheers Jon

Peter_1
27-09-2006, 07:19 PM
Drainwater buidling up in the drainpan, finally the water makes contact with the frosting coil, makes a good contact and starts to freeze, the ice layer grows more and more.
Just a guess ;)

Is the one not cooling the furthest away on the liquid line?

If not, (1st or 2nd, close to the compressor), how have you made the liquid junction on the main liquid line?

Size of liquid line as Samarjit Sen already asked?

icetec9
02-10-2006, 02:02 AM
the liquid line is proper now.
but still has the same problem.
yes i have removed all the ref and is sure of proper ref. r22.
i will see what i can do about getting the size of the condenser.

and im not sure about the the piping of the suction line i will make a diagram of it.

thanks a lot for everyons advice

Peter_1
02-10-2006, 06:38 AM
If you post a questions with the units youre used to work with, place between brackets the other units. So if you normally work with SI units (bar, C, m/h..), place then between these units the proper IP units.

You can do the conversion with a free software program Uconeer
You can find it on http://www.katmarsoftware.com/uconeer.htm#download
Or you can use the spreadsheet of Dan posted on http://www.refrigeration-engineer.com/forums/showthread.php?p=50617#post50617 post 6.

US Iceman
03-10-2006, 01:40 AM
I found unit with 2 of the 3 evaps with a lot of ice on the bottom half of the coil,coming out 5in thick.


This sounds like repeated incomplete defrosts. When a defrost is terminated too soon, the water drips down onto the bottom of the coil and re-freezes. This sounds exactly like what you are describing.

Is the defrost being done by air defrost or electric? How much time is set for the defrost cycle and how often does the defrost cycle occur?



Super heat on all coils are high.The first 2 coils have an uneven frost pattern. With the third with an even pattern. The first 2 coils have a temp diff across the coil of about 12+, the third coil had almost no td at all.


Going off of what was stated above, it sounds like there is insufficient liquid flow to the TXV's.

One other thing I'll comment on until we get some better operating data...

Don't ever rush to to adjust the superheat on TXV's. I find that all too often when the systems don't work, almost everytime someone will start to adjust the TXV.

My experience has been that 9 out of 10 times the fault is somewhere else. OK, maybe not exactly 9 out of 10 times, but it is pretty rare to find a TXV that needs to be adjusted. If they are selected properly and installed correctly, messing with the TXV's is a last resort.

Unless, you happen to come onto a job where the TXV's have been adjusted before.;)

frank
03-10-2006, 07:49 PM
Don't ever rush to to adjust the superheat on TXV's. I find that all too often when the systems don't work, almost everytime someone will start to adjust the TXV.

My experience has been that 9 out of 10 times the fault is somewhere else. OK, maybe not exactly 9 out of 10 times, but it is pretty rare to find a TXV that needs to be adjusted. If they are selected properly and installed correctly, messing with the TXV's is a last resort.

Unless, you happen to come onto a job where the TXV's have been adjusted before.;)

Or you turn up to trouble shoot a new job only to find that all 4 circuits were originally fitted with TEV's rated at 15kw operating on systems rated at 22.5kw :eek:

US Iceman
03-10-2006, 09:26 PM
Or you turn up to trouble shoot a new job only to find that all 4 circuits were originally fitted with TEV's rated at 15kw operating on systems rated at 22.5kw :eek:


Did I read that right? (4) 15 kW TXV's on a 22.5 kW system.

But then isn't it always better to provide more?:p

Another one I ran into many years ago consisted of a commercial split system where the installer had melted the silver solder off of the new distributor and all of the distributor tubes popped out. After several tries to to fix it, he finally gave up and made his own distributor out of a piece of 7/8" pipe. He added some 1/4" tube to the existing distributor tubes to make it easier to handle. Some were now lnoger than others.

He then brazed all of the tubes into the 7/8" pipe on one end. The other end of the 7/8" pipe he connected to the liquid line. Add a lot of refrigerant and presto, done. Time to go home.

The owner of the firm asked me to take a look at the system after they spent a month trying to fix this.

They could not get that TXV to adjust either.:D

Dan
04-10-2006, 02:38 AM
Im working on a walk-in cooler.
I found unit with 2 of the 3 evaps with a lot of ice on the bottom half of the coil,coming out 5in thick. The third coil is not froze at all. This is a R22 system.I let the unit thaw.

This is evidence of incomplete defrosting for these coils. You must lengthen the duration of the defrost. Since you are evaporating at such a low temperature, a longer than normal defrost could be necessary.


Pressures are too low by far, still 190/36-38,, and outside air temp of 80degrees *F.

I agree that your low pressures are too low, but your head pressure is 20 deg f above your ambient. This is not at all low. I agree with Iceman that you are not feeding the evaporators adequately, thus you are underloading the compressor. The question is why?


I found the unit has pressures at 190/36psig.
With a full sight glass. This is a new system of about 8 months. Super heat on all coils are high.The first 2 coils have an uneven frost pattern. With the third with an even pattern. The first 2 coils have a temp diff across the coil of about 12+, the third coil had almost no td at all.

What is an "even" frost pattern? No frost at all? I would think with no change in air temperature, you don't have much liquid evaporating in the third evaporator. What is an "uneven frost pattern? One distributor not feeding? Odd patterns on the return bends?

As with all confusing service calls, we are missing something very simple that will cause you to knock your palm to your forehead once you discover it.

Headmaster valve not permitting liquid flow but an empty sightglass looks like a full one. Restricted filter after the sightglass. That sort of thing. Good luck. Sorry to be of no help. You simply must post the solution to this once you get it sorted out.:confused:

frank
04-10-2006, 10:20 PM
Did I read that right? (4) 15 kW TXV's on a 22.5 kW system.

No - 2 Trane rooftop condensing units, each 2 circuit, each circuit 22.5kw.

The evap had 4 tev's rated at 15kw each.

The systems were losing compressers and had a distinct lack of cooling at high ambient conditions :rolleyes: . Did some calcs and found that the tev's had been incorrectly selected and installed from day one.

Nice little earner that one ;)

US Iceman
05-10-2006, 01:20 AM
I'm not surprised you made some extra on that job. Fixing problems almost always is more expensive than if someone would have done it right in the first place.

I used to do a lot of this type of work. I did not look for it. It found me.:D

Samarjit Sen
05-10-2006, 03:15 PM
I really liked the comments on trying to adjust the superheat by US Iceman. People do not understand that a lot of problems would be created by adjustment of the superheat. Always make the selection of TEV proper and you will not have to touch the same. The problem might be some where else not always with the TEV or the Compressor