Walk-in freeer Compressor blowing start caps

[akelesis]

walk in freezer having issues
Some other company converted the old system from a water cooled condenser to a air cooled condenser which is still located inside the restaurant. approx 4 yrs old
My buddy from work gets called in saying their freezer down, he found a bad start cap, so he replaced it and it worked fine. A few days later i get called back to this site and same thing. Top of the compressor is extremely hot and it wont start. Investiated and discovered start capibilties gone again. start cap is blown. I replaced the start cap run cap and the potential relay (took down the compressor info and got the correct parts for that compressor) Also cleaned the condenser for good measures. incase its getting too high head.
Replaced the parts checked pressures and amps everthing is fine. I got advised by my boss that the compressor is on its way out and to let the manegers know about issue. Now today i get called from my boss that the system is down again. Same issue, but this time he went there to talk to maneger. we are looking to replace the compressor in a few days or even installing a condenser for the roof due to the temperature inside the restaurant.

Just curious is this common thing to happen that this compressor is having a hard time starting and blowing the starting components. is this a good sign of the compressor being bad? Thinking that the people that put in this system didnt do their job of doing a proper vacuum or dirty refrigerant. Is there any other issues that may cause this to fail?




Just wanting some input much appreciated

[Gunslinger]

Compressor bearings could be dragging. Possibly compressor shuts down when satisfied; sometimes armature is in a good position to start and sometimes not.

[timebuilder]

It could be that if the compressor is not running correctly (too slowly) the potential relay is keeping the start cap in the circuit. That would kill the cap.

[markettech]

The only things that come directly to mind that would continually take out a start cap are

(1) Improper part/application (based on the info in your OP though, we can most likely rule that out).

(2) Current/potential relay hanging up (again, being that you changed the relay this would be highly unlikely as well).

(3) Improper voltage supplied to system (is the pump getting a full 120/240V? If not, this could very well be the problem).

(4) Excessive short cycling (any more than ~10 cycles per hour could cause premature start cap failure).

(5) Compressor mechanical wear (See Gunslinger's post).

Personally, I would say this isn't necessarily a 'common' problem as oftentimes mechanical wear will completely lock the pump up or burn out the start winding - and prolonged low voltage/short cycling will usually cause a catastrophic electrical failure in the motor (start) winding long before taking out several start capacitors in succession.

Just shooting from the hip, if your voltage is ok, I'd tend to be of the same opinion as your boss at this point.

[OBogue]

Does it have a CPR valve? An incorrectly adjusted or faulty/nonexistent crankcase pressure regulator valve can cause the same symptom. Excessive crankcase pressure can cause a hard start condition and subsequently kill your start capacitor.

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[akelesis]

thank you all for the responces. this just makes a better tech. i will do a better look the next time i run into a problem similair to this one. all info is much appreciated.

[zxcb]

LL solenoid may be leaking through after the box temp is satisfied, causing short cycling.

[ryan1088]

I was thinking it might be starting flooded....

[steve wright]

That CPR is a big issue if it occurs after defrost. You can actually observe this after defrost it will literally bring start circuit in and out many times. K body (small air cooled) Copelands are especially prone to this.

Failure of the defrost termination circuit will aggravate the problem as the evap will overheat during defrost

[Snapperhead]

LL solenoid may be leaking through after the box temp is satisfied, causing short cycling.

ran across one last week short cycling , I thought it might be the LL solenoid , but turned out was a reed valve was leaking and wouldnt stay pumped down more than 20 seconds .... got a new compressor

[icexprt]

Check all switches in the control circuit to the contactor coil. Usually when we run into this it is either short cycling as already stated, or a problem with a pressure switch where the switch instead of snapping positively open and remaining open, will open/close/open/close/open/ close repeatedly until something blows....start capacitor.

[timebuilder]

Check all switches in the control circuit to the contactor coil. Usually when we run into this it is either short cycling as already stated, or a problem with a pressure switch where the switch instead of snapping positively open and remaining open, will open/close/open/close/open/ close repeatedly until something blows....start capacitor.

Not just pressure switches, either. Recently, I had an ice machine condenser that locked out on shutdown. I replaced the low pressure switch because of the heavy use, but it was poor continuity of the contactor that was the power source for the pressure switches in the condensing unit, and when the contactor chattered it pulled down the voltage in the 208 volt safety circuit, which in turn, meant a loss of coil voltage in the contactor. New switch, new contactor, done deal.

[Sicofthis]

I concur.
I'd bet money something is causing your compressor to short cycle or contacts chatter.

You did not say if you checked voltage at the compressor or if starting and running amps are good.

Edit: reread and found where you said amps were okay.

[nchvac]

Have you megged the compressor?