Screw pack

[headgasket]

Hi can any one help me this screw pack is screwing me up, the pack has two bitzer screws, sorry cant remember the model osn type open, but it is on a 15 ton blast freezer on 404a. no 2 comp is tripping on a general fault IE it could be low oil pressure or hi discharge temp, before any one jumps in with an answer i will tell you what i have done so far.
Changed lead and lag to move the fault to no 1 comp
new oil flow switch
new discharge probe( thermister )
re newed all coils on the pack
renewed all timers in the control panel
new oil filters
oil level to max
moved delta contactor to number 1 comp to see if the fault would move as the feed for the oil return coil comes from an aux on the delta.
cleaned the oil cooler and tested the oil stat oil temp 65c to 75c
the fault can come on every day or two weeks apart.
it is always no 2 comp

[Paulajayne]

Thermistor ???

Paula

[headgasket]

only one thermister and have replaced that, thanks

[bernard]

Alright Mate

How are you,all the screw problems I,ve had have always been oil related,I replaced oil filters that have blocked within a few days,Normally a oil and filter change have sorted the problem.

http://www.att-spares.de/downloads/SP-500-2.pdf




Cheers Bernard

[GHAZ]

Hello mate it,s possible it could be a compressor internal fault i.e pressure relief vavle. When the ambient temperature rises it might cause slightly high discharge pressure just enough to push the weak vavle open towards the suction side in compressor body and pump hot gas

[headgasket]

thanks, this is an all year round fault with low ambient to summer hi

Hi bernard when are you retiring to the bahamas

[NoNickName]

high discharge temp on low load and no liquid injection?
How high is the discharge temp?

[headgasket]

Ciao. there are economizer valves on both screws and they are working, and the system is never under low load conditions, the discharge temp on both screws is 80c about 5c to 10c about oil temp. I am coming to the conclusion that there is problem inside the screw, what, i do not know, i have reached my limit of expertise.

[NoNickName]

Do you mean liquid injection or economizer? They are NOT synonyms.

[Pooh]

Headgasket
you say you have changed the thermistor but have you changed the module that it connects to, I cant remember the model No probably an INT69 or something close. I have had these play up in the past so might be worth a try if you have not already done it.

Ian

[headgasket]

Hi one of the first things i did was to swap the INT69s to try and move the fault, but comp no2 still tripped, then i replaced it, still the same fault. the screw is a OSN 74 open screw, the oil flow switch is in series with the discharge thermistor and has a delay capacitor in parallel replaced this also. sorry nonickname it has no liquid injector. i do not think it is a oil problem as comp no1 is not effected, and when i changed the oil filters they were very clean, but is there any thing inside the screw that would cause high discharge temp. the pack is over 8 years old do they need overhalling.

[monkey spanners]

Hi Headgasket

Could you wire in some Tatle Tale's (wired across Lp/Hp etc they change colour if they trip) to help find which safety device is causing the problem?
We used one in a butchers shop to help prove that the landlord was turning the tennants coldroom off over night (wired across main switch)

Jon

[Andy]

Hi one of the first things i did was to swap the INT69s to try and move the fault, but comp no2 still tripped, then i replaced it, still the same fault. the screw is a OSN 74 open screw, the oil flow switch is in series with the discharge thermistor and has a delay capacitor in parallel replaced this also. sorry nonickname it has no liquid injector. i do not think it is a oil problem as comp no1 is not effected, and when i changed the oil filters they were very clean, but is there any thing inside the screw that would cause high discharge temp. the pack is over 8 years old do they need overhalling.

Hi Headgasket

low suction combined with high head pressure will cause HT faulting. 80 deg c would not trip the int, from memory the Int thermistor goes open circuit at 105 deg c.

Unit wouldn't be short of gas?

Can you measure the suction superheat, if it exceeds the design you will need oil cooling (design is probably 10k max.

Can we have you suction pressure discharge pressure economiser pressure, suction temp, economiser suction temp and discharge temp.

Kind Regards Andy

[bernard]

Hi

These bitzer screws have a guaze strainer fitted on the suction,I reckon after eight years it needs cleaned.

Regards Bernard

[headgasket]

Thanks to you all have taken note, will be back there on Monday to check, if it was a system fault IE low gas,oil, super heat why is it always the same comp even after changing the lead lag.
this is just from memory akv setting 7k sh
suction 1bar
discharge 11bar
404a
external oil temp set for 65c
Hi Bernard will check the stainer, as its the only thing i can check with out striping down the comp

[headgasket]

Up date for andy, call out engineer has just called me
pack suction .2 to .3 bar
comp suction same as above
eco 2 bar
discharge 13.5 bar

[Lowrider]

Suction temperature and liquid temperature?

1 bar suction is -30 dgrC, 13,5 is 31dgrC. So what's superheat and subcool!?

[Andy]

Up date for andy, call out engineer has just called me
pack suction .2 to .3 bar
comp suction same as above
eco 2 bar
discharge 13.5 bar

Hi Headgasket

blast freezing plant then

You may well have a faulty compressor, can you listen to the compressor, bearing wear can be heard on these.

Can you run two compressors together and see what the discharge temps are each.

You may have a motor winding fault kicking out the int unit.

I assume you have a single int69vs for oil ht and motor winding.(the older ones has a 389 unit to do phaseand oil flowe)

No loose conections or burnt contactors on the mains side.

Have you meggered out the motor windings and visually inspected the mains contactors on this compressor?


If all the service filters are clean and you have a good flow of oil at below 80 deg c, it is either mechanical damage in the compressor or an electrical fault.

Usually if the compressor is at fault bin it and fit a new one it might rebuilt, but with reduced effeciency and will go in a years time again.


Kind Regards Andy

[Lowrider]

We have some screw compressors where the winding sensor will trip if it's undercharged. The windings will get to warm and trip!

Did you attach the winding sensor correct? Had some problems in the past where the sensor was placed wrong and motor would trip for no appearent reason!

[Paulajayne]

No 2 comp is tripping on a general fault

Have a look at the wiring diagram and identify what it considers a general fault.

(I have one comp that has High Pressure and High Temperature at the same fault light.) I must get around to changing that.

Then if you can monitor all of the incoming circuits that are reported as a "General Fault" –

Bit of a pain to do but should be worth it.


Paula

[headgasket]

Thanks for all your help, Patience paid off, i was on site all day checking it over and it tripped out at 4.45pm, the fault was a sticking relay on the common control circuit when the system was shut down, there was still a feed to the int69 on comp no2 so it tripped on no oil flow. unberlievable this has taken me eight months to find, i was going to get bitzer out to check the screw, instead i went home and had a few ciders.

thanks again

[Andy]

Thanks for all your help, Patience paid off, i was on site all day checking it over and it tripped out at 4.45pm, the fault was a sticking relay on the common control circuit when the system was shut down, there was still a feed to the int69 on comp no2 so it tripped on no oil flow. unberlievable this has taken me eight months to find, i was going to get bitzer out to check the screw, instead i went home and had a few ciders.

thanks again

Hi Headgasket

a bit of a result than

We have a screw on site where we changed the controls to PLC and Danfoss. Somewhere the wiring is mixed up It was resolved Friday after 6 months. Granted it was a lag compressor, but two engineers looked at it, before we had the control panel guy come back and fit it.

Kind Regards Andy

[lldelfin67]

Hi,
The problem you have is the oil flow is unbalanced. One of the compressor have all the oil and the other is starving for oil. So it could be the bleed valve is not calibrate or lack of oil. You have high discharge temp because the gas is not cooled enough by oil but the discharge pressure is alright. Balance the distribution of the oil flow and it will pass away

[coolhibby1875]

hi there i have been having simalar problem and the fault lay with the drive motor we added grease via the little nipples on the motor and it has solved all the probs ive been having give it a try you just never know

[Eeram]

What is your oil temperature?

What is the compressor model? Open drive or semi hermetic?

[lldelfin67]

Hi,
If you saying that the compressor trip at low oil pressure and high discharge temp. It looks like you have low oil charge or the system oil flow is unbalance cause for low oil pressure at the same the discharge temp will go high because there is not enough oil to cool the gas. Balance the flow and charge oil if necessary

[TXiceman]

Like they say in Texas...

A blind hog will find an acorn ever once in a while.

Patience pays off.

Ken