Marine system, TXv freezing over on one line.

[LeeuwinEng]

Hi everyone,
I work on a ship in australia with a 3 cabinet system (freezer, fridge, fridge) with a redundancy compressor setup(only run one at a time) and seawater cooled condensors
I'm by no means a refrigeration tech, only fairly basic understanding of the systems.

Problem #1(may explain question two)
In the past the system was set up in a way that we could;
isolate power to the compressor in use;
Close HP and LP valves on that compressor;
open the HP and LP valves on other compressor;
run system as normal
since some work has been done weve been told we need to suck down the gas from the compressor in use before we can change over, I dont 100% understand how to do this properly and the fundamental reasons why.

Problem #2 The Freezer and Main fridge "seem" to be operating correctly but the secondary fridge is icing up at the TX valve(if i touch it with moisture on my finger it will stick me to it) and the air from the evaporator fan is no where near cold enough. We have a HP gauge and LP gauge at the compressor units but i dont have one handy to connect to the Schroeder near the TX valve, however i do have an infrared thermometer.

After a bit of reading on here im thinking if there was in issue with refrigerant levels then there would be an issue across the whole system and the pressure levels(at gauges) are consistent with past records. This leads me to think i have to adjust the TX valve in the secondary fridge..
Am I on the right track here or am I out of my depth?
Were at sea at the moment with reception, a possibility of calling a technician out but would prefer to resolve the issue myself.

Cheers in advance,
Mark

[Glenn Moore]

Hi Mark
Question 1 . Not really sure what work has taken place on the unit to require a change in swapping from the Run machine to the Standby, but to carry out a pump down on the running machine before the changeover, simply close the LP valve (thats the cold frosty valve) and watch the LP pressure guage. The pressure should go down to just above 0 Bar at that point ,electrically isolate the compressor and then shut the HP valve (the hot one). Then open the LP and HP valves on the other compressor and let it run.
Question 2 . Again not sure whats happening it could be a simple TXV (expansion valve) element failure fault or it could be the valve on the outlet of the evaporator on that fridge called a |EPR (evaporator pressure regulator) .
If you can give us some more info on what work has been carried out and why we may be able to be more specific as to whats wrong. Please confirm how many compressors and how many condensers on this system ?.

[LeeuwinEng]

Thanks for the reply Glen.
We have a two compressors in and 2 condensers (1 specific for each compressor)

I'v only recently rejoined the ship but the evaporator causing issues had been replaced recently (possibly including TXv in the vicinity) I think the reason was the fan motor had failed and the whole unit was getting fairly old.

I believe i might have messed up in changing the compressors over and have moved the refrigerant around the system. Will the pump down procedure work regardless of what valves etc i may have opened at the same time? I will try again now and hopefully speak to a technician on the phone shortly.

Thanks again for the help, any more would be awesome
Mark

[Glenn Moore]

Hi Mark
That makes a difference to what you have to do when switching from Run to Standby. When you have 2 compressors each with their own condenser you have to think that they are totally independant of each other including the refrigerant charge. The only common parts are the pipe work , valves and evaporators in the 3 rooms.
So when you change from run to standby, before you stop the Run machine you have to shut the valve on the out let of its condenser, this will then suck the refrigerant out from the systems pipe work and evaporators and store the charge inside the water cooled condenser of the Run machine. Once the LP guage has dropped to just above 0 Bar pressure then stop the machine and shut the suction valve on the Run compressor.
Then by opening the valve on the out let of the Standby systems condenser the gas charge from the Standby system will be released, to now run the Standby unit once you open the suction valve and start the Standby Compressor. It may be that you have let the 2 gas charges mix and now you may have one system over charged and one system undercharged.Hope that makes sense Kr Glenn

[LeeuwinEng]

Hi Glen,
That is making some sense actually,
I spoke with a colleague and he had suggested a similar thing.
I think it will be clearer if i label each compressor and valve
System 1 and System 2

Compressor 1 was running with suction valve 1a(cold sweating one) open and valve 1b(from condensor) open.
He instructed to close v/v1b and open v/v2b. As the compressor kept pumping i viewed liquid accumulating in the condenser 1 sight glass over roughly 5 minute period until "half full". The compressor cut out and cycled 2 or 3 times to achieve this, LP staying fairly low <50kpa and HP slowly dropping from <1300 down to <1000
At this point i was instructed to close v/v2b again and then open v/v1b.
I noticed a sharp suction noise and the HP shifted back up to around 1400kpa.
At no point did i open v/v2a, close v/v2a or run compressor 2
Since then the main fridge and freezer systems seem to be working more efficiently but not quite as efficiently as id like(i have isolated the secondary fridge as i think it has its own separate probelm. Should i carry out the same sequence again but for a longer period to draw more liquid into condenser 1?
Thanks again for your help, i guess the best way to learn is to be thrown in the deep end.
Cheffy isnt too pleased though..!
Cheers, Mark

[Tycho]

Mind if I ask the name of the ship?

[Glenn Moore]

Hi Mark
You haven't been keel hauled yet ha ha, but yes it sounds like your on the right track. In the pipe from the condenser out let is there a sight glass ? , if so the sight glass should be clear when the system is running ,so when you shift the charge around do it in a controlled manner ie shift a bit and then close the valve from the non running system and open up the running system and check if the sight glass has cleared. We'll make you a fridgy yet Kr Glenn

[pcvh1976]

hi mate,
i try to understand your problem, but it seems you have a lack of refrigerant. do you have a sight-glass on the condenser? if you have, you need to have a 1/4 level at full capacity (all solenoids open of each cold-room)otherwise you use the sight-glass on the liquid-line (Full cap and check if you see bubbles or not). keep your HP temp at +40C degrees. check the sea water temperature. hopefully you have a water pressure regulator on the sea water outlet of condenser. if not there is a hand-valve, squeeze the valve till you have a optimal HP- temp. check this all first and next you start to adjusting the expansion valves. if you still have a pressure difference (LP) between evaporator and compressor than you have a other problem. a block in the LP line through the bulkheads. it can be icing up and squeeze the pipe flat. hopefully not. cheers

[LeeuwinEng]

hi everyone,
just got back into internet range and have managed to keep the temps ok for the chef.
Both condensers have their own sight glass, then after their respective valves is an accumulator followed by a filter dryer(i think) and another sight glass before heading to the manifold.
We dont have a water pressure reg on the condensers as such but we do have inlet and outlet valves for each condenser so as said i have restricted those to raise the HP levels, unfortunately we only have HP and LP pressure readings not temp readings but its roughly 1400-1600kpa most of the time.

I feel like the TX valve doesnt really respond to any adjustments..
i dont notice the suction line cooling down at all when comparing it to the suction line of the main fridge that is operating perfectly so i think there may be a blockage or a dodgy TX valve, as the liquid line to the TXV is warm.
The freezer is running at about -12C but is set to -18C so im content but not happy with that. The suction line this time is icing over quite heavily but pulls back down to -12 quickly after being open and up to -6C ish for a few minutes.
it all seems fairly stable as it is and were making do with it so im reluctant to mess around anymore in case i stuff up before were back in port. Only have to wait 3 more nights and a tech will be there to sort me out.
Thanks for all the help and input though, i felt a little out of my depth there for a while but alls well.

[LeeuwinEng]

Im the kind of person that likes to read when a problem gets resolved and how for future reference.
Turns out the issue with the galley fridge we were having was the orifice tube in the tx valve was undersized for the job. When commissioned, all three chests had to pull down to temp so the compressor could run flat out. But once the freezer and main fridge were at temp, the galley fridge alone could not put enough load on the compressor to cause it to run. We discovered this when testing the tx valve at the time and found it was faulty(the needle would not move in response to adjustments) we replaced that and tested the system, but was not pulling down enough.

Any way after 3 days back in service the temps are holding well at 4C, 3C and -19C, chef and I are happy.

[Tycho]

When we deliver these kind of systems we wire it so that the freezing room is always running if any of the other rooms need cooling (unless if it is on a defrost cycle)

[Tycho]

The reason why I asked for the name of your ship earlier was because the company I work for delivered a butt load of these kinds of systems with the cool, cold and freezing rooms between 1997 and 2005 as a package with two compressor units pre-charged. so when switching between the two you should just set the "compressor running" switch to 0, close the suction valve and the liquid valve out of the reciever on one unit and open the same valves on the other unit and then turn the compressor switch to the other compressor, and there should be enough charge in the receiver and the pipes to run that compressor.

I noticed when I built and commissioned a system like this while I was still an apprentice that as soon as the freezing room reached it's set temperature the solenoid would close (we used the danfoss EKC for each room)
and the compressor would pump down, because the cool and cold room didn't provide enough to keep it running.
I took it to our brain trust in design, and we changed the control so that the freezing room solenoid would always be open as long as the cool or cold room hadn't reached it's temperature, the only time the solenoid to the freezing room would be closed was if it was on a defrost cycle.

yay for me, we ended up having to rewire 20 systems, I didn't even get a pat on the shoulder

I was thinking if your ship had one of our systems, I could have sent you the revised drawings

[Grizzly]

Hi Tyco.
There are still systems being installed the same control flaws as you describe.
OK when trouble shooting if aware this can happen.
So your post should prove useful to some?
Thanks Grizzly