CIAT Water chiller

[frank]

came across an odd one last week with a 200kw chiller that had been faulting with ice build up on the shell and tube evaporator.

The unit had a sol valve prior to the tev but the LP switch was wired through a timer (solid state).

If the system went into low pressure then the LP switch energised a timer which eventually energised a fault contactor to stop the machine. has any one come across this?

As the comp continued to run in low pressure it pulled a vacuum before the contactor made and stopped the machine With a high vacuum on one side of the sol valve and high liquid pressure on the other the electro coil was not able to energise the sol valve and the machine just ran in a vacuum after it was called.

to solve the problem I had to fit a new Ranco LP, scrap the timer and do a few other mods.

Why fit a timer in the LP?

[Andy]

Hi Frank,
the only time I ever seen that was on scroll compressors on AHU type a/c the idea being that the suction dropped until the head was built up on cold days, and the expansion valves started working.
Regards, Andy

[frank]

Hi Andy

This thing has an 8 cylinder Copeland semi - nice piece of kit - and the condenser has a damper actuator (which is worked off the liquid line) just prior to the fan inlet so head presure is taken care of.

I had to replace the water flow switch which was siezed and causing all the problems but when testing all the safety's this LP really amazed me.

When I left the "modified" machine it was working OK

Frank

[Andy]

Hi Frank,
I am inclined to beleive the L.P short out timer was a quick fix for something that happened in the past. The L.P cutout is a essential safety for a chiller, if the flow fail sticks in flow condition, this is what will save your chiller from freezing.
I would have done exactly what you did.
Kind Regards. Andy

[Dave Goodings]

Alright Frank
what I have seen which is stranger is a oil failure switch used for low pressure safety control on chillers to prevent freeze up where the heater element in the oil failure switch cuts out the chiller if the lp pressure dips for too long strange but does work [cheap solution] one mark might have thought up eh!!! LOL.
Regards Dave Goodings

[CuGe]

Hello Frank,

This is pretty common to have a timer on the LP switch for winter starting. However it should only be able to energise on start up only after that the timer should be out of circuit until the next start up.

[Peter_1]

Nice website Cuge you have

[malik55]

Frank
I had seen some machines with two L.P switches, one for the pump down and one for the system safety cut out, If that was not an original part then may be some one had expericened neusense trips and he added a timer in the circuit for to avoid it. The system will cut out after some time and not immediatly as
at the time when L.P cuts out.