it went off on oil fail

[drcool2002]

hey, this is my new favorite website.
been in the field 3yrs. my own truck doing service 1yr.

--Every time I find a compressor tripped on an oil fail alarm it seems like i run into a different problem. I haven't run into many but i thought you guys could help me out by telling me your experiences with oil fail and if you could take a guess at how many different causes are out there.
THANKS

[rocket]

1. Oil being washed away by Liq Refrig
could be liquid returning during running
or flooded starts (off cycle migration)
2. oil thinned by over heating (or acid)
3. worn bearings and scored cyl walls(caused by 1,2)

Usually #1,#2 come first, as oil fail is reset instead
of finding cause, #3 eventually follows naturally

This covers only 95% of oil trip
Superheat measured at compressor will answer
quite a bit of these

[markettech]

Oil failure can be VERY tricky. Rocket is dead on - but like he said, depending on how the system is wired, it can also trip because of an adverse electrical condition......those will really make you pull your hair out.

I don't think there is a limitless amount of symptoms that will cause an oil trip.....but lets just say there are alot.

[devildawg]

Rocket is spot on but there are many more reasons for oil failure not listed in his post and more than I care to type right now but Compressor contactor failure is also high on the list maybe the number 1 reason that I come across and I see oils fails almost on a weekly basis.

[matt8085]

Ahhhh, the old oil failure mystery. I get these all the time. I try to do a little research on it while i'm there.
Did they lose power? Was there a brown-out of any kind?
Did anyone for any reason shut the evap fans off? Obviously the first thing to check is net pump pressure.
Also keep in mind, the control uses pressure differential, not a float system to determine if the compressor has sufficient oil. I agree with devildog about the contactor. You shoud also take a look at the overload, is it burned or does the bi-metal have a crack in it? Sometimes in low load situations with poor piping the oil will get logged out in the evaporator. By the time you get there, the load demand is high. You hit the reset button and all the oil comes back to the compressor due to the large amount of refrigerant flowing through the system. You should always check the oil sight glass level before you reset. I also find most of the trips are electrical failure of some sort.

[-frozen-ocean-]

i would also check the oil screen it could be plugged. there can be three screens too check
1.crankcase screen
2.oil pot screen
3.sentronic screen
also how do you guys check the contactor when you have a oil trip. is it cause the contactor coil is weak cutting it out?

[-frozen-ocean-]

also when you say at low loads the oil can get trapped in the evap. cause of poor piping what is the fix. do you guys re-pipe the suction line or add a riser. or a trap? or is there a way to get around this problem?

[devildawg]

poor piping can be a cause but thats something thats usally low on the list unless your working in some mom & pop type location,usually when the piping is determined to be the cause a simple oil separator installed at the compressor is the most cost efective way to fix it.

[-frozen-ocean-]

devildog how do you determine the contactor is the cause of the oil trip

[markettech]

Originally posted by -frozen-ocean-
also how do you guys check the contactor when you have a oil trip. is it cause the contactor coil is weak cutting it out?

Basically, you will be looking for worn points or a contactor that does not move freely. Depending upon the wiring, a compressor may single phase or otherwise trip on overload and the oil control time delay will kick out on a safety even though the compressor is not running.

Again - oil failures are probably one of the hardest to diagnose because there are sooooo many causes of a tripped control

[-frozen-ocean-]

thanks for the input! i will forsure check the contactors in the future.