Need answers on a freezer....

[ToddH]

I've got a refrigeration system on one of my rental trailers that is having some issues that I've never come across before in my 16 years of working on this stuff. Let me give you a list of the components and a run down of what I've done to try and repair the problem.

The box is 6'x8'. It has Copeland condensing unit model# EJAL-A100. The compressor is a Copeland model # KAEB-007E-CAA. The evaporator is a 5400 btu with a BFSE-AA-ZP TXV. System runs on 404a refrigerant.

The problem I'm having is that the box won't pull cooler than 40-45 degrees. I did a compressor efficiency test and it would only pull to 2 inches in a vac, so i put a set of valves in it. That changed nothing. So I checked the TXV and it didnt seem to be feeding the coil. It also took a long time for the fans to come on because of that. So I opened the valve a round and nothing changed again. So I put a new valve and nothing again. The system is running 35 lbs of suction and 320 lbs of head pressure. I checked for pressure drops in the system and I'm only getting 2 degrees TD across the evap coil. This thing also has a new condensor on it because the old one had a leak a couple of yrs ago. This thing was running great until afew weeks ago. Hopefully I made some kind of since in describing my problem. thanks in advance for the help.....

Todd

[Gary]

What's the subcooling and superheat?

[Gary]

That 2F TD I assume is the air in minus air out temps. That is the delta-T or dT, not the TD. The TD is air in minus saturated suction temp (SCT), which in your case is about 40F TD.

The dT is way too low and the TD way too high. I'm betting that the superheat is also way too high... all of which tells me that the coil is starving.

Since this is a new TXV, either the system is undercharged or there is a restriction between the condenser and the TXV. Plugged drier... or kinked liquid line? Wherever the restriction is there should be a temp drop across it.

[ToddH]

I do have a clear sight glass and I have checked for a pressure drop from the reciever tank to the TXV thru a tap that I welded in 2" before the TXV. The coil is starved no doubt. I can get the first set of loops to frost and it takes quite awhile for the fan delay to come in. I don't know the superheat at this point because I have the TXV wide open and cant get it to feed all of the coil.

[Gary]

I do have a clear sight glass and I have checked for a pressure drop from the reciever tank to the TXV thru a tap that I welded in 2" before the TXV.

Then that narrows it down to that last two inches... or the TXV itself. Does the TXV feed into a distributor? If it does, then add that to the list.

[Gary]

You might want to disconnect the TXV and blow backwards through the coil to see if it flushes anything out of there.

[ToddH]

I've flushed everything 9 ways to sunday. And yes it goes into 3 distributor tubes. And I just added the tap at the TXV to check the pressure drop from the reciever tank so I know the last 2" is clear.

[Gary]

The evaporator is a 5400 btu with a BFSE-AA-ZP TXV.

Hmmmm... the ZP charge in the TXV bulb is a pressure limiting charge. This chokes off the flow to prevent the suction pressure from going too high and overloading the compressor.

We need to check the high side stats to see if it is pumping a full load:

Condenser air in/air out temps
High side pressure
Liquid line temp near receiver

[ToddH]

This particular piece of equipment is on a small insulated trailer in our rental fleet so every time this thing goes out it starts working with a high box temperature. Lately it's been starting with a 85-90 degree f box temp during our "repairs". (haha). I do know that the head has been running around 310-325 lbs with a full sight glass. I was hoping once I cleared it it would bring it back down under 300. As the box gets cooler the head might get to 300 even. The air inlet and outlet temps I don't remember off hand ( I didnt do the test) but I do recall only a 6 degree differential. I haven't checked the liquid line temp but I can tell by the good old hand test it seems way too hot to me. I took the discharge line off yesterday to look for a possible restriction but nothing was found. also keep in mind this is a relatively new condenser that is very clean. Thanks for the help so far Gary.

[Gary]

I can't see it from here. The only way I can "see" what the system is doing is if you give me accurate temperature and pressure measurements.

[lowcool]

apply water over condenser to see if pressures improve,maybe condenser is to small or its configuration of piping maybe incorrect.

[ToddH]

Lowcool- I sprayed water on the condensor and got 250 lbs of head for 45 minutes and only pulled 5 degrees out of the box.

Gary- What are all of the reading you need? when I get in monday morning I'll get these and report back in the evening. Thanks again.

[Gary]

Evap air in temp
Evap air out temp
Low side pressure
Suction line temp at TXV bulb

Cond air in temp
Cond air out temp
High side pressure
Liquid line temp at receiver outlet

[ToddH]

I'll get those and post tomorrow...

[lowcool]

heat exchanger on evap internal split ?

[Magoo]

Way back you did a compressor check, and acheived a 2inch vacuum. Something wrong there, I am not familiar with compressor, but maybe an internal relief is bypassing.
OK with a suction gauge on service port and you close the suction valve the compressor suction should invert itself to a low vacuum.
If the bypass is passing you are a mission to nowhere.

[ToddH]

Low cool- No heat exchanger.

Magoo-This is a brand new compressor. And do the Copeland K bodies have an internal bypass? I don't believe they do? I believe the suction pressure would change if it was bypassing.

[abet_meneses]

ToddH,

Thinking that you have a blown gasket around valve plate assembly.

[ToddH]

I got the measurements today and I did it 2 ways. The first batch of numbers are with the evap fans off on fan delay. The second group is the the fan delay jumped out. Here's what I came up with.

Unit started at 1:16 pm. Unit was running 20 minutes when these numbers were taken.

92*f box
98*f ambient

Cond in:92*f
cond out:110*f
High Side pressure:310 lbs.
Liquid line temp @ reciever:100*-114*f
Low side psi: 40lbs.
Suction line temp @TXV bulb:6*f

30 minutes later, still with no fans.

65*f box temp
98*f amient

Cond in temp: 98*f
Cond out temp 107*f
High side pressure:290lbs
Liquid line temp @ Reciever 99*-108*f
Low side psi: 33lbs
Suction Temp: 1.6*f


Here are the numbers with the fan delay jumped.

Unit started at 2 pm.

72*f box temp
99*f ambient

Cond in temp:98*
Cond temp out: 112*
High side psi: 310lbs
Liquid line temp @ reciever outlet: 114*

Evap air in:71*f
Evap air out:68.4*f
Low side pressure:48 lbs.
Suction line temp @ TXV bulb:70.5

Last numbers taken at 3:30 pm.

53*f box temp
99* ambient

Cond temp in: 100*
Cond temp out: 112.7*
Highside psi: 310lbs
Liquid line temp @ reciever outlet: 114.3*f

Evap air in: 55*f
Evap air out: 53.5*f
Low side psi: 45lbs
Suction line temp @ TXV bulb:54.5

Hopefully I have everything you needed to kind of help steer me into some direction on this thing. This is the 1st one thats ever stumped me. Hopefully I can understand the terms because you fellas are alot more educated on this than I am! Thanks again...

Todd

[lowcool]

ok fellas why the high head pressure if comp is stuffed unless hes converting discharge temperature to pressure

[Gary]

Is the new TXV an exact replacement? Same model numbers as the old TXV?

[ToddH]

Lowcool- no conversion on the pressure.

Gary-This particular TXV no it's not. I went with the exact one before and it wasn't feeding enough either. This one was recommended for me to try.

[tbirdtbird]

If U are certain the evap and the dist tubes are free of obstruction it would surely seem to be the TXV from your numbers

[Magoo]

If the compressor sucks a blind suction to 2inch vac.., there is a problem with bypass somewhere. Your call as to where.

[Gary]

Lowcool- no conversion on the pressure.

Gary-This particular TXV no it's not. I went with the exact one before and it wasn't feeding enough either. This one was recommended for me to try.

What were the original numbers?

[Gary]

I have been searching for information on the ZP charge. They just say that it is a pressure limiting charge. Nobody is saying what pressure it is limited to.

[lowcool]

magoo it does sound inefficient but if blowpass is there,why the exceptional head pressure whilst running yet suction pressure is down.maybe non condensables or a roosters bum feathers in the system and a possible restriction in the liquid phase of condensing,maybe pump compressor down a couple of times to see if better than 2" can be achieved with a different set of clocks and leave to see if it holds it.only mentioned that if temp was converted to pressure it could be mistaken for heat of compression.whilst system has been recovered for non condensables fit a DANFOSS valve rated to coil and reprocess system with a different bottle of refrigerant.

[ToddH]

I will get the #'s off the old TXV tomorrow. I had a manager of my wholesaler talk to an engineer for their company and he said they were supposed to be limited to 35-40 lbs. The reason I had him call was I had seen 50-55 lbs at times. That's the other reason i haven't set super heat. I have to get the box cold enough to get off of the MOP of the valve to set it.

[ToddH]

Lowcool-I've used a couple of diff pair of guages to make sure mine were working correctly. The compressor will pull very little vacuum, but it will hold. It will pull a 29 inch vacuum with no head against it. I also used a different bottle of 404a when I recharged it thinking It was a crazy batch of gas but it changed nothing either.

[Gary]

Highside psi: 310lbs
Liquid line temp @ reciever outlet: 114.3*f

Ahaaaa...

R404A @ 310 psi = 120F

120 - 114 = 6F subcooling.

Add refrigerant until the subcooling is 15F. That clear sightglass must be an empty sightglass.

And that 310psi should be up around 350psi for a heavy load in 100F ambient.

[lowcool]

when checking superheat across the evap is the outlet colder or warmer than the inlet temperature

[ToddH]

Gary- the original TXV was a FSE-1/2-ZP. And this thing has had a clear sight glass all along running 310 PBS of head pressure.

[Gary]

Clear sightglass or not, the subcooling says it is undercharged.

[ToddH]

how do I figure subcooling so I can get to that magic number?

[Gary]

how do I figure subcooling so I can get to that magic number?

Find the saturated condensing temperature (SCT) by converting high side pressure to temperature with a P/T chart.

Measure the liquid line temperature near the receiver outlet.

SCT minus liquid line temp = subcooling

[ToddH]

So I keep adding gas til 15 is achieved? I'll report back tomorrow! thanks again.

[Gary]

Check out this thread:

http://www.refrigeration-engineer.co...ad.php?t=19701

[Gary]

So I keep adding gas til 15 is achieved? I'll report back tomorrow! thanks again.

Yes... until the difference between those two temps is 15F.

[Gary]

Any progress today?

[D.D.KORANNE]

Compressor :
Is there a way you can check up leak back of valve plate ( valve reeds ) on compressor ? Or ask copeland to supply these numbers . Probably reed leak back could be an issue.

[rooboy]

Hey Gary

Can I just ask how you came about to decide that this system needed 15k subcooling. Is there a formula to be used that will decide upon the most efficient subcooling figure ?
In the past I have always worked on 4 - 6k subcooling, but recently I found that I had greater performance with 12 - 16 k subcooling, however I am not sure how the systems will handle 40+ deg C ambient.

Thanks

Rooboy

[Gary]

Hey Gary

Can I just ask how you came about to decide that this system needed 15k subcooling. Is there a formula to be used that will decide upon the most efficient subcooling figure ?
In the past I have always worked on 4 - 6k subcooling, but recently I found that I had greater performance with 12 - 16 k subcooling, however I am not sure how the systems will handle 40+ deg C ambient.

Thanks

Rooboy

That's 15F, not 15K.

15F/8.5K is the maximum subcooling without backing liquid up into the condenser and raising high side pressure.

There have been situations where the liquid needed to pump upwards to the evaporator and I have gone as high as 20F/11K subcooling to avoid flashing at the TXV, but that's pushing it.

[Magoo]

Did you vapour or liquid charge R404A into system after changes.
magoo

[rooboy]

Gary

Thanks.

I'll start another thread just on subcooling and get everyone's thoughts

Rooboy

[yoelyeve]

Id think that the system is over charged and the condenser and evaporator becomes part of the receiver device