What's wrong with the compressor?

[Break7]

Hi everyone I need help with a compressor. It is a copeland semi hermetic 2Hp low temp. Problem is it istripping the overload and blowing start caps. It is working really hard but it is still pumping.It is slowing down enough that the potential relay is dropping out and killing the start cap. It is supposed to take 16 amps but it is taking 55amps.It only runs about 10 seconds at a time. The wierd part is it sounds like very high head pressure but it is normal. And if you shut it off while it is running it sounds like it runs backward for 2-3 secs like a car that diesels when it's hot. Anybody have any Ideas? I'm kinda new so please bear with my novice diagnosis

[mad fridgie]

Some conflicting info.
How do you know it is pumpimg OK?
What are your pressures when not running, when you start what do your pressures go to. Do not use what is used to do, but what it is doing now.
Are 100% sure the discharge service valve is open? Measure the pressure using one of the head ports, if you are unsure.
The only recips i have seen that "run on" are one with either a broken crank/drive shaft or all conrods/big ends have come detached (also broken)

[Break7]

The resting pressure on the high side is about 120psi at the service valve. When started it rises to about 235 before it trips the overload. The low side is about 70 and pulls down immediately.

[mikeref]

Break7, sounds like stator and rotor interference from damaged bearing. can you see the oil level when compressor is off? Also, any history available prior to this problem?.. Mike.

[Break7]

Thanks for the reply Mike. I can see the sightglass. It looks full about 90% up. As for the history All I know is that it has been changed twice before.

[powell]

Break,

What is the model of the compressor and what refrigerant are you using. Other info such as the evap model would help us analyze the system.

[Break7]

I've changed the compressor and the freezer is running again. I opened the compressor and checked it out. The shaft turns effortlessly even with the ports blocked off.? The oil looks good ,Smells good. The windings read about 1.2 megohms to ground though. And the shaft has a lot of end play like 1/2 an inch. I also found the unit was almost completely out of gas. Will that wear it out prematurely? By the way it is installed out doors and it is very cold in the winter (as low as 0 F). I installed a new crankcase heater just to be safe.

[monkey spanners]

Sounds like it has got shunted windings.

They do have a bit of endfloat on the crank, i think there is a light duty spring in the motor end that keeps the crank in place during normal running.
Any wear is more likely to be in the bearing on the piston end of the crankshaft or the big end bearings.

[Break7]

I think your exactly right Thank you all for the replies I'll do more autopsy Monday.

[Break7]

I opened the compressor and ran it.It starts slow but gets up to speed. With the ports wide open it's running 33 amps, a bit more than the 14.6 it is rated at when at full load. The ohm meter shows that the run winding is slightly less resistance than it should be. The compressor died because the low pressure cut out failed. The compressor was running in vacuum until the liquid line valve opened when the t-stat called. For hours at a time maybe. It may have run continuously for days!