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  1. #27
    Join Date
    Aug 2010
    Location
    Dearborn MI
    Posts
    377
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    Quote Originally Posted by emptech View Post
    On this particular compressor, I did not see an oil path to the two main bearings. The original bearings had a circular groove in the middle, the replacements had the grooves in a cross pattern. There is an oil path through the center of the crank from the oil pump that feeds the two rod journals and the oil path continues to the motor. I'm not sure exactly how the main bearings (bushings) got their oil, splash?

    Getting back to the beginning, there was a leak in the system, no low pressure switch, the system ran out of refrigerant (R404A) and continued to run until it had a vacuum. Eventually one of the rod journals froze up. I don't think the oil pump failed entirely, but I replaced it anyway.

    Today I will pressure test the crankcase for leaks, my vacuum didn't hold but I question my micron gage that may be leaking.

    For pressure testing, the saturated pressure of 404 at 60F (as if the compressor ever got that cold) is about 120psi, so I don't see a problem with leak testing around that pressure or somewhat above, I just didn't know if I could pressure test it with 200 - 250 psi. I'll do that today and report back. If I can't find a leak with pressure I will assume my problem is my vacuum system, all the hoses, ball valves, etc.

    Jim
    The crankshaft has a hole between the two main bearings that intersects the slightly pressurized oil passage drilled the length of the shaft. Oil comes out between the bearings and enters the bearings via the grooves in the bearings. If you noticed, the rotor bolt is hollow and has a small orifice hole drilled in the end of it. The size of the hole is what keeps the pump from failing because it acts like a pressure relief. Pressure over x number of psi squirts out of the hole and into the motor side of the compressor where it then flows back into the crankcase side.

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  3. #28
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    21,735
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    Let's hope the correct rotor bolt was reused.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

  4. #29
    Join Date
    Nov 2010
    Location
    Sacramento, CA
    Posts
    42
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    Thread Starter
    The system is working, but without my pressure switch, now we continue...

    Question, I need to be assured that this freezer will not ruin the compressor if it should develop another leak. It is a True 49F, 49 cubic feet, semi hermetic, low temp, as you should know by now. I don't know the date of manufacture, but it has no pressure switch/s. My thought was to put a low pressure switch on the high side somewhere. The system uses R404A. I chose a MARS B16-950, opens at 75#, resets at 100#. My thought looking at the PT chart, 100# would exist if there was a saturated liquid at 50F or above, so if the system lost refrigerant and the pressure dropped below 75#, the compressor would not start up, and if the pressure was always above 100#, the pressure switch contacts would be closed or reset.

    It seemed like a good idea, except that when the system reaches setpoint, the hi pressure drops down to about 32# until the compressor starts up again. I've realized there is no liquid in the high side of the system where I was thinking there was. I'm not sure where the 32# comes from, but coincidentally looking at the PT chart, zero degrees F gives a pressure of 32.1#. The box temp is set to around zero F, perhaps that's where the 32# comes from.

    I think I've found all the leaks in the system and have put a lot of time into rebuilding the compressor, the customer cannot afford another failure, but I'm not ready to have them fill it with food and me to walk away from it, I need some kind of failsafe. What do other low temp refer systems use?

    If that's the case, I'd want a pressure switch in the high side that would be set somewhat under 32#, right? If that's the case, don't believe that MARS has one in that range, then I'd have to go to an adjustable switch. What do you think, how would you protect the system? What pressure would you set the switch to?

    Jim

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  6. #30
    Join Date
    Jan 2010
    Posts
    15,806
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    I've never seen a refrigerant safety on a True freezer but this will do it. You would need to install a relay if there isn't one already.
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