replaced evap icing up.

[wannafreeze]

In a food warehouse freezer my boss had me replace an evaporator coil.Compressor is 7.5 HP.I don`t know much about evaporator sizing ,not able to give any number now,maybe tomorrow..It`s a hot gas defrost system with some kind of liquid heat exhanger.(Kramer).There is another evaporator 10 feet next to it connected to an identical condensing unit.The old evaporator has also two fan motors but in the back of it and blowing the air towards the coil whereas the one I installed has two fans in the front drawing the air through the coil.I have been having problems with the one that has the new evaporator.I adjusted the r408-a charge in both units the same way.Pressures were in the same ranges when I adjusted the charges.On the new evaporator I measured 12*F superheat as unit was up and running for a while.The expansion valve positioning and insulation is OK.My problem is suction line on the new unit gets iced up to the compressor because the coil gets frozen up before it can perform its job.Previously I found the cancelled X wire in the panel and after some wiring puzzels managed to activate the defrost termination.So I was able to make frequent and looong defrosting.After a week got a call.Found out a 25 amp fuse I previously replaced for a 30 amp one blew out because of blocked air flow around the condensing unit.So I had the blockage removed and put two 30 amp fuses.Meanwhile while checking the defrost clock I left it in 20 minute defrost lenght.Soon enough had to go back there too see the big compressor became an iceball.Incresed the derfost time to max again.But still something is not normal.I shouldn`t be defrosting so frequently and looong,when the other evaporator has no such situation.Tomorrow I am going back there to check the unit.I am thinking about increasing the superheat.Also suspecting of wrong evaporator selection.

[refer dude 2479]

If this is a krammer unit make sure you have the piping to the new coil right and that all of the solenoid valves and check valves have been installed properly. Sounds like you are missing something in the patented Kammer defrost system. These work pretty good when installed properly. Is the new coil a Krammer coil???

[refer dude 2479]

Sorry, can't spell tonight. Should be Kramer

[wannafreeze]

Originally posted by refer dude 2479
Sorry, can't spell tonight. Should be Kramer

The new coil is Russhel..I piped it the same way the old one was.And my spelling sucks too.
even after a long defrost meaning I can see inside the coil the ice is long melted that plate of 1\4 in.ice doesn`t wanna fall.it blocks the air.

[Dad]

My thoughts on the SH would be to get it a little lower than 12*. Can you get it to 8* and keep your compressor amps within specs?

Remember that 408 is not a 100% charge drop in.

edit:

It also occured to me that you may need to check on your distributor nozzel. Did an orifice come with the new coil? If so, which one did you install in the distributor?


[Edited by lusker on 08-03-2004 at 09:16 AM]

[R12rules]

Originally posted by lusker
It also occured to me that you may need to check on your distributor nozzel. Did an orifice come with the new coil? If so, which one did you install in the distributor?


[Edited by lusker on 08-03-2004 at 09:16 AM]

Good point.

[frozensolid]

If that’s a thermo bank system, your defrost should be terminating on pressure. It is possible you are terminating at to low a pressure. You should have two pressure controls in the control cabinet. One for defrost termination and one controlling your suction stop solenoid valve.

The terminator should be set to 195-200# pounds with 408a and should be reading pressure upstream of you holdback valve. Many may call this a CPR but it is not a CPR though it functions very similar to one. A thermobank when switched into defrost pushes all the liquid out of the receiver, and into the evaporator. Then into the suction line with the suction stop closed, all the liquid backs up behind the holdback valve and is metered to the compressor. To ensure enough hot gas for defrost.

When defrost terminates, your suction stop stays closed. Until the pressure downstream of the holdback valve is below the setting of the suction stop pressure control (this setting is determined by compressor amps). Once below this point, the suction stop opens and your chilling again.

If you look at your spider you should be able to tell if you have an orifice installed. It should be frosting all the tubes evenly.

Double check the check valves inside the coil for proper orientation also.

[Edited by frozensolid on 08-03-2004 at 07:32 PM]

[icemeister]

For those who have no clue as to what a Kramer Thermobank system is, here's a link to a PDF explanation of it.....with diagrams and stuff. ;)

http://www.kramerusa.net/misc/product_information/SPLIT_REFRIGERATION_SYSTEMS/THERMOBANK_FULL.pdf

Altan......is it the coil icing or the compressor icing that concerns you the most here? If you have 25-40 Deg F compressor superheat you're in good shape even if the compressor is encased in an iceball. If the coil is iced up enough as to prevent airflow then that's a defrost problem.

That Thermobank defrost should be fairly rapid and quite complete. Follow frozen's exquisite advice and proceed from there.

[wannafreeze]

Originally posted by icemeister
For those who have no clue as to what a Kramer Thermobank system is, here's a link to a PDF explanation of it.....with diagrams and stuff. ;)

http://www.kramerusa.net/misc/product_information/SPLIT_REFRIGERATION_SYSTEMS/THERMOBANK_FULL.pdf

Altan......is it the coil icing or the compressor icing that concerns you the most here? If you have 25-40 Deg F compressor superheat you're in good shape even if the compressor is encased in an iceball. If the coil is iced up enough as to prevent airflow then that's a defrost problem.

That Thermobank defrost should be fairly rapid and quite complete. Follow frozen's exquisite advice and proceed from there.

I didn`t go there today.Even if I was there I wouldn`t have read the responds I am reading delightfully now almost midnight.But I understand there are a lot of points to think about.Also thanks for the web address,which I will check in a free time.As far as two pressure controls,I remember there is one dual pressure control.And one inside the panel that would open the liquid line solenoid valve upon completion of defrost bringing the back pressure to around 0 psi and then energize the LLSV,if I remember correctly.Frozensolid seems to be an expert on this one,.thanks.
I didn`t get any orifice with the new evaporator didn`t even think about.
Compressor being an iceball freakes me out because it happens when the evaporator is blocked,otherwise I know it doesn`t automatically mean that there`s liquid going into the compressor.I didn`t measure SH at compressor yet.

[gerryboy00]

Originally posted by altan
There is another evaporator 10 feet next to it .The old evaporator has also two fan motors but in the back of it and blowing the air towards the coil whereas the one I installed has two fans in the front drawing the air through the coil..


???

[icemeister]

I think what altan was saying is that the old Kramer unit was a blow through unit while the new Russell is a draw-thru type.

[wannafreeze]

Originally posted by icemeister
I think what altan was saying is that the old Kramer unit was a blow through unit while the new Russell is a draw-thru type.
yes sir.also today I stopped by there everything looked fine.Just before defrost I saw the unit with no ice anywhere.

[refer dude 2479]

Originally posted by altan

Originally posted by icemeister
I think what altan was saying is that the old Kramer unit was a blow through unit while the new Russell is a draw-thru type.
yes sir.also today I stopped by there everything looked fine.Just before defrost I saw the unit with no ice anywhere.
So was ther a problem and what was the fix. Was it just the slab of ice that you had trouble getting rid of or........

[wannafreeze]

Originally posted by refer dude 2479
So was ther a problem and what was the fix. Was it just the slab of ice that you had trouble getting rid of or........ [/B]

I think there was\is a problem.After I found the missing X wire and activated the coil`s DTT and put long defrost time every 4 hours the DTT`s bulb sensed the front of the coil which melts the latest ,it was fixed.Now the customor thinks the unit is in defrost everytime he passes by the compressor.The front part of the coil where the DTT bulb is not totaly defrosted when the rest of the coil is already dry.I just don`t want to take chance with an iced up coil.

[condenseddave]

A Thermobank.:eek:

Pass the Excedrin.