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Kevin Yeo
07-12-2005, 08:12 AM
Dear all,

I have seen one jobsite that is having constant problem with compressor 1 (oil pressure tripped).

Refer to sketch, could it be suction header design problem?

Crankcase pressure equilizing and oil equilizing line are present. Each compressor has its oil regulator (to receive oil from oil receiver) and SV, energised only when compressor cut in.

Any idea to solve the problem

Thanks,
Kevin

chillin out
07-12-2005, 08:36 PM
Refer to sketch,
What sketch?

Have you cleaned the oil filter inside the comp?

Just a guess.

Chillin:) :)

Big Cube
07-12-2005, 09:04 PM
Sounds like the either the compressor oil filter or the suction filter.

Big Cube

aeb200
07-12-2005, 09:08 PM
Have you verified the low oil presure by putting your guages on a service port???

some types of oil pressure switch have a common fault, especially ones on carrier equipment

take the cover off the switch - the may be a little heater (looks a bit like a capacitor), check that this is hot. if it isn't replace switch

regards aeb200

US Iceman
07-12-2005, 11:29 PM
Put gauges on the compressor suction service valve and the Schrader fitting on the oil pump (or install a fitting if none is available).

The difference between the oil pump discharge pressure and the suction pressure is the net oil pressure. (I am assuming this is a semi-hermetic reciprocating compressor)

You should see about 25 psi of net oil pressure. This is an estimate. You should check the compressor manufacturers data to see the normal net oil pressure.

I have seen oil pumps go bad and the oil pick-up strainers get dirty.

You should also check the oil safety switch to make sure it drops out the safety circuit after the heater trips out the warp switch.

Cofreth
08-12-2005, 03:44 PM
R-22 with Bitzer compressor?

Darren W
08-12-2005, 08:11 PM
If your pressure readings etc. are correct, you could have liquid refrigerant coming back to the compressor,this mixes with the oilthus reducing the oil pressure. If so, a suction accumulator should solve your problem.

chemi-cool
08-12-2005, 11:18 PM
What make is the compressor and the oil pressure control?

Chemi:)

Kevin Yeo
09-12-2005, 09:12 AM
Dear all,

Its bitzer 2 stage 30 hp compressor.
Oil pressure diff make : danfoss
Oil regulator make : AC&R

Rgds

Cofreth
09-12-2005, 03:18 PM
High possibility a blocked oil screen.

US Iceman
09-12-2005, 05:40 PM
Kevin,

Thanks for the drawing...

This is typical for most installation with multiple compressors. One thing I can warn you of is the last suction line on the header. Whenever liquid refrigerant returns to the suction header, the last compressor on the header will always have the most problems with liquid.

The liquid flows through the header, hits the end of the header, and splashes into the last suction line connected. I have seen this happen on ***** and ammonia systems. It is very common.

If liquid gets into the crankcase, the liquid refrigerant has a very low viscosity. The oil pump will try to pump the liquid refrigerant, but due to the low viscosity, the pressure does not increase.

You did not say if the compressor having the problem was the last one on the suction header, but this could be one possibility.

Does the system have a suction accumulator???

Peter_1
09-12-2005, 09:44 PM
This is a good start for some of us http://www.bitzer.de/_doc/k/kt-602-1.pdf
I posted this also in another threrad: student question

Gary
10-12-2005, 06:31 AM
Sometimes it has nothing to do with oil pressure.

An electrical problem can cause the compressor to cycle off on it's overload, but the oil pressure control is still energized.

Since the compressor isn't running there is no oil pressure, so the oil pressure control kicks off.

Then the overload resets itself, and you are left thinking that it is an oil pressure problem.

Peter_1
10-12-2005, 01:10 PM
This is in my opinion more a mis-wiring instead of an electrical problem, especially because you know on forehand that this failure could happen.

The OSD may never be energized as long as the compressor isn't running. If an auxiliary contact is mounted on the overload, then this must be used.
If not, then the connection must be made direct on the leads to the compressor.

I have a colleague of mine who takes a lead wire direct from the compressor connections and insert then an in line fuse (glass) between the line to protect it legally.

He also connects a small switch in the wall of the compressor electrical enclosure between the Kriwan or the OSD device contact so that he can switch it off when he's working on the compressor.

BESC5240
13-12-2005, 08:52 AM
Since it's a two stage compressor, it could be that the injection on the intermediate stage causes the problem. (solenoid or TEV of the interstage stays open/blocked with dirt). The low pressure of the OPDS (Oil pressure differential switch) is the cranckase pressure, which is at intermediate pressure. The intermediate injection happens just before the gases comming from the low stage enter the motor compartment (and then entering the crankcase). If there's too much liquid injection, oil and refrigerant mix and oil pressure drops.

Reg
31-12-2005, 03:00 PM
just a guess, but have you checked your crank case heater? A bit chilly this time of year!!

abdulazman
31-12-2005, 10:35 PM
Kevin,
Was it an old installation or a new one.Check all your parameters. Check your oil filter. If its clean, possibility of liquid flood back. Check your superheat.

Andy W
01-01-2006, 01:43 PM
Was it an old installation or a new one.That would be my first question, also has it always been ok and only just developed a fault? What you could always do if the other 3 work ok is start to swap components from the other ones if you want to go to the trouble, this way you won't mis diagnose the fault. Some one mentioned the overload tripping causing the problem, I have had this so many times, usually better to wire the ODPS through an auxillary of the contactor to prevent this. Liquid coming back is always a favourite but you will usually see it, does it happen while you are on site, can you actually see it happen.

Kevin Yeo
06-01-2006, 06:18 AM
Dear all,

I changed the vent valve for oil reservoir from 10# to 20#. Check all solenoid valve feeding to oil regulators. Adjusted the regulators slowly to get balanced oi. It has been running 2 weeks w/o any trips.

Cheers,
Kevin

C Bagtas
07-01-2006, 03:45 AM
In semi hermetic compressor (carrier)If i got below 20 psi oil differential pressure,i replace the oil pump.Or maybe your oil is less,sometimes if the system is less gas and somebody put jumper in low pressure switch,the oil will pump to the system.you can check it in sight glass of compressor.

Peter_1
07-01-2006, 09:44 AM
What can go wrong so badly with an oilpump that you have to replace it?
Inside are only 2 gears :confused:
System must be very muddy inside.
And the oil seeve just before the pump???

chillin out
07-01-2006, 04:06 PM
I agree with Peter, I have never changed an oil pump before and I have had some really $hitty systems.

What make of comp are you talking about?

Chillin:) :)

rpbuenaflor
07-01-2006, 04:11 PM
Probably your oil pump slightly loose compression, check your oil Delta P

RUDI

rpbuenaflor
07-01-2006, 04:17 PM
Im not talking to what make, what Im saying the type of comp which is semi hermetic type.

TONY_MF
08-01-2006, 12:35 PM
just only the oil pressure switch selection, please refer to catalog

abdulazman
08-01-2006, 12:41 PM
Normally in the catalog they say '' Please refer to the manufacturer for further detail ''. Thank you.

TONY_MF
23-05-2006, 03:53 PM
hi Kevin, make it sure your oil separator is working properly. check the oil u-trap and p-trap at the system if correct? at night check it how they closed the cabinets. this is for showcases only. if all this was meet your satisfaction. check your oil regulator. this is your problem.

Andy T
26-06-2006, 11:05 PM
sound like one of are systems.Make sure the cases are not iced up. Are all fans working in cases.May be pushing liquid back and washing the oil.What color is the oil.If it looks dark you may have a reed blown on the comp and the suction pressure on the sump side is kept high and so the oil pump can't lift the pressure above suction pressure.

mr cool
11-07-2006, 11:07 PM
check oil pressure against suct and compare against diff setting on oil press switch, is it a new comp, i have known of press sw lines being fitted to oil pump without removing schreader core or having a core depressor so not regestering any oil pressureto o.p.s. also is it the last control device in circuit, if not it may be stopping on themistor or lp/hp, stopping comp and then timing out on o.p.s. as there will be no oil pressure there. does it do it all the time or once a week or so?

shylockw
12-07-2006, 03:20 PM
Is this a Rack? Only Compressor 1# is often bad?

If so, the factors for oil filter, suction filter and back refrigerant will not only affact compressor 1# oil failure.
Maybe possible reasons is that Oil Diff reading is not set correctly or Oil pump is bad.
:o

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13-07-2006, 12:12 AM
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