Bunker defrost problem

[etterold]

I have a Hussman R507 rack, controlled by a Emmerson E2.The system in question is operated with a sporlan CDS9 epr. There are 6 evaporators all with CDS4 (D/T bunker). On this system there is two evaporators (one side) that are not getting enough defrost and ice up after a few days. No other systems (24 in total) on the rack are having problems, and this is not the farthest run only 120 ft el.DDR valve is operating at a 25# delta p.defrost time is 18min with a 1min drip (Hot gas).The E2 is showing the CDS4 open 100% on defrost with the main 0% Does anyone have any ideas as to what could be causing this problem?

[flyinkiwi]

Hmmm. Emerson. Sporlan. 'Nuff said.

All brandism aside (I actually quite like E2s and Q-bodies...not so keen on RMCC though)...

Am I correct in assuming that by bunker you mean static/gravity coil?
And also that each Evap has its own CDS4 as an EEPR?

1. What is your ET/SST?
2. Are all evaporators in the same room?
3. If so, do all evaps defrost simultaneously?
4. How long are the cable runs to the CDS4? Is there a cable segregation/interference issue?
5. What percentage of rack load do these circuits represent?
6. What expansion device is fitted?

This might be somewhat irrelevant if I'm not think of the same system you're describing. Hate to say it but, "I'm from Missouri. You're gonna have to show me." :-)

If defrost is simultaneous, I would investigate the possibilty of a lack of heat available for effective defrost.

Otherwise, I look foward to seeing some more juicy details of the system!

[etterold]

Sorry about the brandism. I call a bunker a frozen food open top island H*****N mod # FWG the island has 6 evaps all forced air. This is a new install and has worked this way from the start. This island is D/T (dual temp) and has a CDS as a epr on each evap in the island.

1/ SST is -25 deg f
2/ All evaps are in the same island. 1 on each end
and 2 on each side.
3/The island is one system and defrosts at the same
time (the system epr closes and the ones in
the island open)
4/The calble is 14ga belding and the run would be 100'
I rewired the splice on one of the CDS4 in
question to see if that would make a difference
5/The percent on defrost at the same time is 3%
6/Sp**lan txv

I have attached a picture of what I am taking about only mine has two end sections. Different areas different terminology.
:)

[Gary]

In hot gas defrost flow through the coil is reversed. Hot gas enters the suction, liquid condenses in the coil and is pushed backwards into the liquid line. There is usually a check valve bypassing the TXV to pass the reversed liquid flow. If the check valve sticks shut the coil will fill with liquid and the defrosting will slow down or even stop.

[Gary]

Observe the defrost operation to be sure hot gas is entering the coil.

Also make sure the coil is bottom fed (liquid line on bottom) so that gravity is delivering the liquid to the liquid line (through the check valve).

[etterold]

There is a check valve around the txv. the problem I am seeing is the CDS seems not to have td across it all the time thus not feeding all the time during defrost (at times there is td across the CDS. That would lead me to belive they are not working correctly, yet they are working correctly in refrig mode.As I state this is a new install and factory piped cases

[etterold]

I am new to CDS valves an I am unsure of the test procedure.

[Gary]

There is a check valve around the txv. the problem I am seeing is the CDS seems not to have td across it all the time thus not feeding all the time during defrost (at times there is td across the CDS.

At defrost start is there flow?... and then flow stops later in the defrost cycle?

[etterold]

Yes the CDS seems to open and you can feel flow through the valve then it stops and after a few min it startes up again, very sporadic. The E2 is programed to open the case CDSs to 100% on defrost (main system epr closed 0%).Thus I would think that once the hot gac is there it should stay there, unless I have a bad connection in the control wiring going to the CDS. Causing it to step open and close, yet it holds very constent temp druing refr state. I redid the connections on one of the valves to see if that makes any differance. Now it is just the waiting game to see.

"You have to love technoligy I rember in the old days when all was mechanical. you did not have the service calles as you do now. Close controlling and monerting is good for the customer and good for the service company".:D

[Gary]

Yes the CDS seems to open and you can feel flow through the valve then it stops and after a few min it startes up again, very sporadic.

I'm thinking the sporadic flow is the check valve opening and closing, thus starting and stopping the flow.

Do the non-problematic coils do the same thing or is their flow continuous?

[Gary]

The fact that all of the other systems are defrosting properly indicates that there is sufficient differential pressure between the hot gas and the liquid, but possibly the new check valves require a little more differential pressure to open. You might try increasing the differential pressure and see if that solves the problem.

[etterold]

The fact that all of the other systems are defrosting properly indicates that there is sufficient differential pressure between the hot gas and the liquid, but possibly the new check valves require a little more differential pressure to open. You might try increasing the differential pressure and see if that solves the problem.

This is a new store so all the checks should be good.I really think it is a problem with the CDS4 it doesn't take much to cause a small voltage imbalance and that may be my problem, ie poor connections.

[smilies]

If I suspected the CD$'s in the cases themselves, I would swap a couple known good connections on the board and see what happens. You did not post any temp diff's across the valves or check valves. In the cases in question I would also strap a temp clamp on the liquid line after the check valves and compare that number to the good cases.
If the cases are not piped right (telescoping piping) then that will be a problem as well, more so with a Kool gas setup.

[hussman]

I'm also leaning towards piping cases wrong or to small of a liquid supply line witch limits kool gas return. On the obvious is the check valves.

[Slatts]

This is a new store so all the checks should be good.
Hi etterold. I think what you wrote there is what's called an oxymoron.
It is normal for a new store / installation to have teething problems.
As often as not caused by the installation techs or the original equipment manufacturer.
The company I work for makes a very tidy living from this fact.
one of our major national companies comes in, upgrades an existing supermarket or does an install in a new shop then leaves town. We then make a very tidy living sorting out the problems they've left behind.
It's been a few days now. Have you had a win?