Can anyone tell me what to do here or have any suggestions?
You are working on a 42°F smoked meat walk-in cooler that has had a complaint of tripping the oil safety control about once a week. You check the oil level and find it is at ˝ glass when the cooler is nearly ready to shut down. Since this compressor is remote is uses an automatic pump down cycle. When the thermostat is satisfied the compressor begins pumping down, you notice the pump down takes a long time to complete, upwards of 5 minutes. You install gauges and find that the system is indeed slowly pumping down marked by a steady decrease in low side pressure but during this time the oil in the sight glass is foaming up violently and the net oil pressure is dropping from 30 psid downward. What is the problem or what would you test/check next? Is there any additional information you need?
First of all welcome to the site.
I see your a student so we'll ask to have this moved to the Tech to Tech section of the forum, as the jobs section is "For posting resumes and general discussions about jobs [aka employment]. To post HELP WANTED you must be a Professional Member of this site. If you do not meet this requirement your post will be removed. No Unauthorized Recruiters may post."
Notice each section of the forum has a description.
A pump down taking a long time to complete would make me wonder about a liquid line solenoid leaking, compressor valves....
More information needed. Refrigerant, Pressures High and low, actual measured temperatures on the liquid line and suction line. Yeah superheat and subcool, but let us do the math/double check yours.
*Also how long between cycles and how many times does it pump down between actual cycles?
Last edited by crab master; 09-21-2011 at 11:10 AM.
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I've seen this movie before. The oil pressure switch is usually on some kind of a timed circuit (to give the compressor enough time to come up to speed and pressure the oil switch). Sad to say i've seen in some designs where the oil pressure switch will show as a sympton even though the compressor is not running (leading one to think he has a oil pressure related problem when in fact the compressor not running is the problem). then of course your troubleshooting should be directed toward compressor not running. hope this helps.
I also would suspect the valves and/or the liquid line solenoid. Is there a suction valve on the compressor? If there is, front seat the valve and turn the system on. The system should pump down into a vacuum. (You may have to jump out the pressure switch to achieve this.) Once in a vacuum (hopefully 10-20 inches) it should hold there without rising back towards zero. If it rises, jump out the pressure switch again and stop when 10-20 inches vacuum is achieved. The pressures should hold at 10 to 20 inches in a vacuum and if the pressure continues to rise on your suction side your compressor valves are bad. This an easy way to check them. (All of this is assuming that there are no unloaders on the compressor)
Thank you guys for the advice, much appreciated! Sorry for posting in the wrong place, still learning the site, will put other posts in the correct area, thank you!
What is the condition of the motor contactor's points?
One of the most overlooked causes of an oil trip.
The other stuff is important, too.
Originally Posted by marsmech
I agree with Marsmech. This is a good place to start as long as it is a reciprocating comp. No need to try on a scroll