lp trip then working

[klobber]

working on a carlyle compressor/ sea water chiiled/ dx coil system, the system branches into 4 liquid lines with solenoids and has a hot gas bypass, its ancient! the system does run however it cuts out on l.p...... resetting the lp at the panel most of the time does not work..... however it has just worked there and has ran for a bit then cuts on l.p and easily resets a few times... then restting doesnt work..... it runs at 40psi suction/140psi discharge....its 417a.... the sea water regulator valves dont adjust and the the coil is un-accessable due to not being able to shut water supply off.... anybody that could give me help/info??... bit inexperienced..... and have 120 people on an oil rig to keep cool....
klobber......

[monkey spanners]

What you need to work out is,

1. Is the lp tripping at the right pressure? (has its settings been altered from when the system ran R22? for instance) If yes, then what is making the suction pressure too low, if no, then its either adjust or replace time (i prefer replacement on important systems)

2. Is the air flow good through the evaporator?

3.You have four solenoids in the liquid line presumably for capacity control, are they all working?

4. Is the hot gas bypass working? i presume it is to keep the suction pressure up during low load conditions.

5. Is any capacity control/unloading working ok on the compressor?

6. What can be done about the low head pressure? This may cause a low suction presure too, especially if no modifications/adjustments have been made to the expansion valves when the R22 was replaced, (i think R417A require a greater flow for same duty but could be wrong)

This is just general stuff i have thought of, i haven't worked on that type of system so...

Jon

[shaaf]

hi dear

liquid line filter drier partially block
faulty soleniods
some time exv. has strainer may be its partially block
some times condition are different than explanation.

[Grizzly]

If none of the above.
Based upon your discharge pressure, which appears a tad low!
I would try and throttle in the sea water flow through the condenser.
You do need to sort out the regulating valves.
Otherwise the excessive subcooling will be an issue!
Which can cause LP cut-outs.
Bearing in mind these replacement refrigerants, can be between 10-25% less efficient.
Cheers Grizzly

[stuartwking]

Klobber,

The condenser regulating valve sounds like it could be causing this problem. what is the the subcooling/ Delta T across the coil?, I would also look into you Hot gas by pass,. Is there a receiver with sight glass or liquid line sight glass? is there sign of liquid?.
Is this feeding 4 different coils?. what is the super heat and Delta T across these?.