Compressor Knock problem

[AC90]

Hi there to all at RE!!!

My first posting, and in need an experianced word, with trying to troubleshoot a knocking freezer 3ph compressor on start up.

Over the summer a freezer door was left open which caused damage to a ball shut off valve and compressor, semi hemitically sealed. When inspecting the system, in running the system the TLV was hissing into the evaporator so I shut the system down and changed the compressor, filter dryer and valve.

On pressure testing I found that the condensor was leaking so I repaired the leak. The system held pressure. I vaced down the system and charged with the correct amount of 404a.

Switching the system on the compressor ran smoothly on the first startup pulling the temp down efficiently. On its second pulldown there was a lound knock on start up. This happened on the next two startups. Slightly worried I have powered down the system and pumped out the refrigerant.

Can anyone help in pointing me in the right direction with the problem of the compressor on startup. I noticed frost forming around the suction pipe into the compressor.

The system is a basic walkin freezer comprising of the following:-

Telemacanique compressor 3Ph.
filter dryer
TLV
accumulator

and all the other goodies.

Hope you can help.

AC.

[Grizzly]

Welcome.
It may be that you are pulling liquid back.
Have you set/ checked the superheat. What do you mean by TLV??
Cheers Grizzly.

[AC90]

Hi Grizzly!!

Thanks for replying,

Sorry I meant the Expansion Valve.

Any thoughts?

Thanks very much,

AC.

[AC90]

No sorry, I haven't checked the superheat as I was a little worried wether the compressor would sustain damage.

thanks again,

AC.

[monkey spanners]

Is the system on pumpdown or has a liquid line solenoid valve? Could be letting by if fitted and filling the evaporator with liquid when the system is off, or if solenoid not fitted could be the same thing.
Does the compressor have a properly working crankcase heater?
Does the accumilator have a heater?

Jon

[p_p]

I agree with grizzly, it sounds like you're getting liquid back to the comp.



PP

[Grizzly]

M.S./ P.P.
Have it also what we are all suspecting is liquid carry over, hence the questions about liquid control and the subsequent boiling off of the liquid.
To repeat check that the comp has a working crankcase heater. The heat will boil off any refrigerant within the crankcase.
Also this may be a stupid question but are the evap coils clear and do the fans run correctly.
Because blocked evap coils will cause liquid flood back.
Can you confirm Wether the compressor cont actor or the liquid line solenoid valve shuts upon the system reaching set point.
Or is it passing? If the LLV is sound you should be able to remove it's solenoid coil screw in the exp valve to raise the S/Heat. Did you set it up to the manufacturers setting?
If the clonking is due to liquid hammer and this is yet to be proved.
All of the above should help sadly it is difficult to second guess what is happening.
But hopefully you are getting an idea of what to look for and how to go about it?
I hope it is of help and let us know more?
Grizzly

[AC90]

There is a solonoid valve in the liqued line which I checked and seems to be closing and opening (audibly) when the system starts & stops. The crankcase heater is working fine too.

Thanks so much for the advice, I will go and cover all of the aspects and will be straight back.....

Thanks so much for your patiance.

AC.

[Brian_UK]

There is a solenoid valve in the liquid line which I checked and seems to be closing and opening (audibly) when the system starts & stops. AC.
Does the valve close before the compressor stops or at the same time?

[AC90]

Hi again,

Sorry being away for a while still troubleshooting the compressor knock problem. I stripped the solinode valve down to find 2 small filiments of copper on the diaphragm, which were embeded into it where it seats itself. I carefully removed the debris and recharged the system.
Sadly still having the same problem of the compressor clanking on its second and following startups.
The solinode valve seems to close just before the compressor shuts down and opens just before it starts up again.
I have spoken to a couple of technicians who work on a ship and they mentioned if all else fails change the expansion valve. What are your thoughts with this next step??

Thanks for all the help here and advice, and most of all your patiance.

AC.

[nike123]

Hi there to all at RE!!!


The system is a basic walkin freezer comprising of the following:-

Telemacanique compressor 3Ph.
filter dryer
TLV
accumulator

and all the other goodies.

Hope you can help.

AC.

Do you have pump down?
Check your superheat.