Contactor single phasing after 4 days

[darcy.welch3]

Working on a ref plus remote unit for a coffin/bunker freezer, the system will burn the contactor lags out within 4 days causing it to single phase and go off on oil failure. I am having trouble as to why the contactor lags are burning out cause i am having proper voltage across all three phases, proper amperage, no bleeding through the contactor, it does not chatter, i have an auxilary switch on it so that the defrost and compressor never run at the same time and i have made sure that the contactor is properly sized. Any ideas?

[jpsmith1cm]

it does not chatter,

Are you SURE????

I mean REALLY, REALLY, SURE?

[refrepairman]

Are you SURE????

I mean REALLY, REALLY, SURE?

Ditto-something must be causing chatter to burn it out this soon.

[darcy.welch3]

I am watched it for probably 5 hours turning it on and off, cycling it through defrosts and pumping it down can not find a way to make it chatter, every time i show up it is running properly once the contactor is changed

[Freezeking2000]

I am watched it for probably 5 hours turning it on and off, cycling it through defrosts and pumping it down can not find a way to make it chatter, every time i show up it is running properly once the contactor is changed

ICM Delay on make, set for 5 seconds or more.

[jpsmith1cm]

ICM Delay on make, set for 5 seconds or more.

Not a bad idea.

Only other thing is contactor sizing?

Is the contactor big enough for the load?

[Freezeking2000]

I assumed the contactor was rated properly....what is the contactor rating?

Is it possible the compressor is flooding back and locking up? Do you have superheat numbers?

[darcy.welch3]

Superheat is 15 degrees at the compressor and 8-10 at each txv, there is 6 txv in the bunker, the contactor is 40 FLA and 50 Res the max circuit of the unit is 25amps

[cavalieri85]

Take amp draw on condenser fan motor. Maybe it's failing periodically and causing chattering off hp switch.

[timebuilder]

I would check every contact in the coil circuit of the contactor, too.

[darcy.welch3]

Okay thanks everyone for the input

[Capz]

Assuming the cables & contactor are both sized for the amp capacity, check you cable ends. Are your cable ends burnt up? Did you cut them back exposing clean copper? Is the control voltage solid? This and what others have already stated.

[cmclifton]

I recently saw a head pressure switch that was intermittently causing contactor chatter. Seems like it's gotta be something like that.

[HVAndyC/R]

Had something similar on a wif freezer last week. Happened to catch it in the act. Was checking between L2 and T2 at the time and was getting a sporadic voltage drop. Quickly went back to the disconnect and had it there. Disconnect wasn't always making good contact. It was at a restaurant and every time they loaded the freezer they shut it at the disconnect. Changed it out and gave them a pump down switch.

[timebuilder]

Not long ago, I had a contactor problem on a Manitowoc rooftop condensing unit. The control circuit is 208 volts, fed from the line side of the contactor, and a low pressure switch is used for de-energizing the contactor when the unit pumps down due to a closed solenoid down in the ice maker head.

The low pressure switch contacts started to cause a chattering, then each time the contacts closed, the high compressor starting current pulled the voltage down which made the chattering even worse. Because the voltage drop was different each time the pressure switch operated, the unit could be making ice normally for up to a week or two.

The fix was to replace the damaged contactor and the pressure switch.

In this instance, the fact that line voltage was used for the control circuit was a key element in the problem, and it was difficult to find the cause because the switch did not always behave in the same way.