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g.karsandas
29-12-2008, 08:35 PM
Hi,
The air conditioner having 20 hp semi hermatic compressor, trips on low oil pressure some time.The temperature of the cold room is to be maintain around 6 degree centigrade ,and the atmosheric temperatur of the (Winter)vary from -2 to -15 degree centigrade.
Seeking help.
Thanks,
g.karsandas

Andy
29-12-2008, 10:01 PM
Hi,
The air conditioner having 20 hp semi hermatic compressor, trips on low oil pressure some time.The temperature of the cold room is to be maintain around 6 degree centigrade ,and the atmosheric temperatur of the (Winter)vary from -2 to -15 degree centigrade.
Seeking help.
Thanks,
g.karsandas

Hello g.karsandas:)


6 deg c seems low for A/C normally without defrosting.

Would the unit be freezing up then carrying liquid back to the compressor causing it to go out on oil.

Kind Regards Andy:)

g.karsandas
29-12-2008, 11:42 PM
HI Andy,
You can say it is a cold storage.It does have a defrost,it operate once in 24 hours.The defrost timer is kept for 1/2 an hour.
Thanks,
Gkarsandas

US Iceman
30-12-2008, 01:34 AM
Is the compressor in a warm room or is it sitting in the cold air?

Without crankcase heaters on it, you might see the same problem... The oil is diluted by liquid refrigerant in the crankcase. Even thought the refrigerant is liquid the oil pump will not generate sufficient pressure to keep the oil safety switch closed.

g.karsandas
30-12-2008, 01:02 PM
Is the compressor in a warm room or is it sitting in the cold air?

Without crankcase heaters on it, you might see the same problem... The oil is diluted by liquid refrigerant in the crankcase. Even thought the refrigerant is liquid the oil pump will not generate sufficient pressure to keep the oil safety switch closed.

Hi Iceman,
The condensing unit is on roof top.The unit is having crank case heater.Defrost timer is set for half an hour, and once in 24 hrs.It runs good but some time it trips.
Thanks,
g.karsandas

abet_meneses
30-12-2008, 01:24 PM
g.karsandas,

what brand is that low pressure control?

regards,

US Iceman
30-12-2008, 01:41 PM
Hi Iceman,
The condensing unit is on roof top.The unit is having crank case heater.Defrost timer is set for half an hour, and once in 24 hrs.It runs good but some time it trips.
Thanks,
g.karsandas

Does the switch trip sometime in the defrost cycle?

Does the unit have a pump down solenoid valve?

g.karsandas
31-12-2008, 07:55 PM
Does the switch trip sometime in the defrost cycle?

Does the unit have a pump down solenoid valve?
Hi US Iceman,
I dont have idea as defrost timer is kept at midnigh.
Yes unit have punp down solenoid.
g.karsandas

Toosh
31-12-2008, 08:40 PM
Hi,
The air conditioner having 20 hp semi hermatic compressor, trips on low oil pressure some time.The temperature of the cold room is to be maintain around 6 degree centigrade ,and the atmosheric temperatur of the (Winter)vary from -2 to -15 degree centigrade.
Seeking help.
Thanks,
g.karsandas

HI Just a thought what controls the head pressure in low ambient temperatures

Norm

WINJA
01-01-2009, 03:31 AM
Is the oil preasure safety wired last in the control circuit?
Ie thermistor then hp/lp switch then oil preasure switch

Andy
01-01-2009, 01:17 PM
Hi US Iceman,
I dont have idea as defrost timer is kept at midnigh.
Yes unit have punp down solenoid.
g.karsandas

Hello g.karsandas:)

probably a good idea to move the defrost to during the day to see if the trip is before, during or after the defrost. This would also let you see if the defrost is fully clearing the frost and ice.

Kind Regards Andy:)

tonyhavcr
02-01-2009, 12:07 AM
Air conditioner tripping on low oil pressure now are you shore its triping on oil or is the compressor trying to start but gose off on overload and the o.p.s. times out. I had this some time back. or is the o.p.s. one of these setronic where the serscer sits in the oil they need to be remved and cleaned.

g.karsandas
02-01-2009, 02:50 PM
Hello g.karsandas:)

probably a good idea to move the defrost to during the day to see if the trip is before, during or after the defrost. This would also let you see if the defrost is fully clearing the frost and ice.

Kind Regards Andy:)

Hi Andy,
It seems to be tripping by night.
I am going to change the defrost timing during day time.
Thanks,
g.karsandas

Slatts
04-01-2009, 11:16 AM
gedday k.G, is this a new system that's had the oil problem since it was installed or is it an old system that has run fine till recently?
Do you have some sort of head pressure control on it?
What's your operating head, suction and oil pressure?
What type of compressor are we looking at?
What's the temperature of the suction line at the compressor?
If you can answer all these questions it may make it easier to work out what is causing your problem.
Cheers,
Slatts

Slatts
04-01-2009, 11:25 AM
Almost forgot, What refrigerant is in the system?
What type of compressor is it?

g.karsandas
07-01-2009, 02:26 AM
Almost forgot, What refrigerant is in the system?
What type of compressor is it?

Hi,
It is Copland semi hermetic,with R 22 refrigerant.
Thanks,
g.karsandas

Slatts
08-01-2009, 08:48 AM
Hi,
It is Copland semi hermetic,with R 22 refrigerant.
Thanks,
g.karsandas
Thanks g.k but what about the rest of the info I asked about in the previous post?
Did moving the defrost to day time make any difference?

markdenford
11-01-2009, 07:38 PM
sounds to me like the system is not getting enough defrost, if the room is to maintain +6c (chiller) it should have 6 defrost in a 24hr period! i take it oil level is ok/filter ok? has system got oil seperator on it?

Enthalpy Eng
14-01-2009, 05:29 AM
I ran into this type problem on a freezer that had a condensing unit on the roof, discovered a faulty OFS (Johnson Contrls) last in cct to the comp contactor.

had to Re&Re it....
The OFS first took a pounding from controlling 208V cicuit, but what I noticed is that when the unit got close to satisfying some liquid would make it back past the Accumulator and washout the oil going through the oil pump. the OFS then would trip out after a 90 second time out.

I ended up checking the superheat to the comp and noticed that it was to low @ around 5, I increased it to 18 by (patiently) adjusting the TXV. the system works fantastic now....

Slatts
14-01-2009, 09:53 AM
sounds to me like the system is not getting enough defrost, if the room is to maintain +6c (chiller) it should have 6 defrost in a 24hr period! i take it oil level is ok/filter ok? has system got oil seperator on it?
Gedday Mark. The number of defrosts per day is related to the duty of the room (how heavily the room is used eg; the number of times the door is opened), ambient conditions (Temperature and humidity),type of stock in the room and coil TD.
On a little used room, full of cans of drink installed in a dry, air conditioned room, you may well get away with 1 defrost per day.
Horses for courses mate.


I ran into this type problem on a freezer that had a condensing unit on the roof, discovered a faulty OFS (Johnson Contrls) last in cct to the comp contactor.

had to Re&Re it....
The OFS first took a pounding from controlling 208V cicuit, but what I noticed is that when the unit got close to satisfying some liquid would make it back past the Accumulator and washout the oil going through the oil pump. the OFS then would trip out after a 90 second time out.

I ended up checking the superheat to the comp and noticed that it was to low @ around 5, I increased it to 18 by (patiently) adjusting the TXV. the system works fantastic now....
Enthalpy, I take it you haven't been doing this long?
Sounds like the oil safety was just doing what it was supposed to do.
You need to check the SH at the evaporator.
Set it up at 4 to 6K at the TX valve bulb then check your SH at the compressor.
Since the system has a suction accumulator you should have heaps of SH at the suction service valve once the TX valve is set up properly.
If you just shut the valve down to get some SH at the compressor you could still be either flooding the coil and suction line, there by increasing the suction pressure and wasting capacity or you could end up starving the evaporator and loose capacity that way.

Either way we seem to have misplaced the OP.

Enthalpy Eng
15-01-2009, 02:45 AM
Enthalpy, I take it you haven't been doing this long?
Sounds like the oil safety was just doing what it was supposed to do.
You need to check the SH at the evaporator.
Set it up at 4 to 6K at the TX valve bulb then check your SH at the compressor.
Since the system has a suction accumulator you should have heaps of SH at the suction service valve once the TX valve is set up properly.
If you just shut the valve down to get some SH at the compressor you could still be either flooding the coil and suction line, there by increasing the suction pressure and wasting capacity or you could end up starving the evaporator and loose capacity that way.

Either way we seem to have misplaced the OP.[/QUOTE]

nope in my case the OFS was faulty........

Slatts
15-01-2009, 08:38 AM
nope in my case the OFS was faulty........
Fair enough. Did you check the superheat at the evap, or just at the compressor?