Short cycling Comp/solonoid

[Gaz6388]

Im having problems with a walk in cold store, the condenser is cycling on
and off via the low pressure switch not because the system is uundercharged I think this is down to the solonoid valve passing or the compressor passing which is the best way to determine this??

[mikeref]

Restriction in refrigerant flow, or ambient is low. Is this happening after reaching temperature or during the cooling cycle?

[Royal241]

if the solenoid valve freezes (or gets cold) at the end side (in OFF position) then it leaks through, there might be something stuck preventing the pin to close. to check compressor: pump down closing the king valve, observe suction pressure, it it rises, then the compressor is leaking backwards. if replacing the compressor is an expensive thing, then install a time delay ( on make ) to the compressor contactor (set it like 5 minutes), that will increase the compressor lifetime (but will eventually get stuck), I've seen compressors like this run for a couple more years...

[1torr]

Is the solonoid valve de-energised? Even if it is, the comp may still cut in a few times on the LP, just to boil off any gas in the low side. Cheers

[monkey spanners]

Shut the reciever valve and see if it still does it (after its had time to pump down)

If it still doing it then its possible its the compressor valves.

[Grizzly]

All of the above offer sound advise and yours is a knowledgeable assumption.
As the guys agree proving the problem should not be to complicated.
I do have one related question, what's the state of the evaporator like?
If partially restricted or filling incorrectly, even partial oil logging with cause the LP circuit to fluctuate!
( boil off, as 1torr explains!)
Your on the right track already, you just need to be able to spend some time with the problem Gaz.
Follow the guys and your own advise and I am sure you will get there?
Grizzly

[The Viking]

All of the above +

Have you checked the cut out / cut in pressures of the LP switch (real life values, not what the markings say)?



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[Grizzly]

All of the above +

Have you checked the cut out / cut in pressures of the LP switch (real life values, not what the markings say)?



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Good point Viking!
If the diff on the lp switch has been set to low, then short cycling would be exaggerated.
Not that any of the other guys points are less valid.
Interesting one this, I hope you let us know how you get on Gaz.

Grizzly
Grizzly

[chemi-cool]

When it runs? doe's it work ok? pulls temp down as expected? Doe's compressor head gets very hot?
Are there cold spots along the liquid line when it runs? drier not cold?

[Gaz6388]

First of all thanks for all your advice!! Ok to answer some of your questions....
evap coil isn't blocked, when comp is called for fridge temp comes down to 3.0c no probs,
once at temp and comp isn't called for solonoid shuts and it goes off on lp, temp before and
after solonoid seems the same, head of the comp was getting slightly warmer than normal but not too hot to touch, temp seemed to be the same before and after the liquid line drier and I didn't notice any cold spots on the liquid line. also once the unit switches off on lp I get a constant hissing noise.this was only a maintenance visit so I've just reported it so I'll just have to see if I go back to it.

[Royal241]

nice, clearly a backwards sound (compressor)