Tip & How-To about Refrigerators

Nusance tripping of oil pressure control on commercial refrigeration

Oil pressure trips on semi-hermetic compressors aren't a problem you'll run into every day,however when you do they can be a real pain in the neck to diagnose and repair. Here are a few things to check for when troubleshooting an oil safety trip.
The obvious place to start is to check that there's oil in the compressor. Check the level in the sight glass. If the oil level seems low but the compressor stays running, watch to see if the level increases after 10 or 15 minutes of run time:

* If the level doesn't increase, add enough oil to maintain about a half a sight glass.

* If the level increases, then the oil was logged out in the system and is now returning. A flooding expansion valve can cause this problem.
Monitor the superheat at the compressor, and watch for foaming oil in the sight glass.
Freezers without a pressure limiting expansion valve can have this problem when coming out of defrost. Use a crankcase pressure regulating valve.

A bad three-phase contactor can cause oil safety trips. The oil safety is wired in series with the compressor contactor, so if the compressor intermittently single-phases due to a voltage drop across a burnt contact, it won't start. In these cases, it's common for the compressor windings to overheat, and for the internal overloads to open.

The oil safety can still be energized and time out. Without a pressure differential, this will trip the oil safety after 90 to 120 seconds. The contactor will open, and the compressor will cool down. Then you show up, reset it, and it runs. Because you find no oil pressure problems, you leave only to return in a couple days to the same problem.

Oil pumps are protected by a filtering screen located in the oil sump of the compressor. If the screen become plugged with debris picked up from the system by the returning oil (anything small in the system, such as solder scale, dirt, copper burrs, etc. will eventually end up in the compressor) it can give you the illusion that the oil pump may be failing.

Before you change the oil pump, check and clean the screen.

Use a good suction line drier as well as a liquid line drier

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why does the P28 oil pressure differential switch trip when the compressor is not running


Could be a relay, short in a wire. fuse. Sounds like a compressor issue, i would have it checked out. Could be the pressure trip?

Aug 23, 2014 | P28DN-1 Lube Oil Protection Control

1 Answer

excessive air pressure buildup that's blowing safety valve and can hear air leaking inside unit.this compressor is only about a year old!thankyou.


Excessive air pressure...if your safety valve is truely popping off, is caused by a bad pressure switch or a loose wire connection at the switch. It's a little odd to be leaking too. There is a couple a possibilities here. The most common spots for leakage is the "tube seal", the aluminum transfer/supply tube, or the outlet air hose. Usually a leak will keep a unit from acheiving full pressure causing the unit ot run continuously. The other common leakage spot is the "check valve" and a leak here usually makes the auto restart (upon using air from the tank, taking pressure below the set lower limit), not work,stalling the motor and popping a breaker. See ereplacementparts for a proper breakdown and identification of parts. Spliting the clamshell is a "pain in the neck" for these little units, but you"ll likely have to do that to find your internal leak. Carefully avoiding electrically exposed parts, spray a soapy water solution at suspected joints if the leak is not obvious.

Oct 20, 2012 | Dewalt D55141 Oil-Free Hand Carry...

1 Answer

how much oil does a 1/4 hp compressor motor take


is it hermetic closed compressor? if it is you do not have change oil.
if it is half hermetic and have freon also not change,
if it is air compressor then change oil after 500 hours,use oil especially for compressors,not recommended to use motor oil.

Feb 22, 2009 | Samsung Refrigerators

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