Bunn manual SERVICE cont COMPRESSOR EMBRACO ULTRA-2, Check Compressor Windings for Ground Fault

SERVICE (cont.)

COMPRESSOR (EMBRACO) (ULTRA-2)

Compressor Windings & Related Component Testing:

Note: Measure the resistance (ohms) between termi- nal pins C&S and C&R around ambient temperature of 77° F. Add the resistance between C & S and C & R. The sum should equal the resistance found between S & R. A 10% deviation is acceptable.

Continuity must be present between C & S and C & R. If there is no continuity on start or run winding, there is an interruption within that winding.

Check the C (common) compressor winding to com- pressor ground terminal/housing. If continuity is present, one of the compressor windings is shorted to ground.

Check Compressor Windings for Ground Fault:

Upon removal of the protective terminal cover, if evi- dence is shown by any lead or terminal being over- heated, it is a good indication that a compressor wind- ing problem may exist. Follow the recommended step below to check the compressor winding insulation. If a ground fault is detected with the compressor, keep the power off, thermal protector and potential relay disconnected. A licensed certified refrigerant techni- cian will need to replace a defective compressor.

Testing Compressor Windings/Insulation with a Meg- ger

A megger is a preferred test over using a typical ohm meter for testing the compressor windings. The meg- ger checks the insulation factor of a winding making sure it is actually insulated and not leaking current (Ground Fault). An ohm meter usually produce a low voltage for reading resistance verses a megger uses higher direct voltage source to measure insulation re- sistance to detect a breakdown in the motor winding insulation.

Step 1: Disconnect all electrical power to the BUNN ULTRA-2 HP.

Step 2: Access compressor terminal pins and discon- nect the wire leads going to the compressor pins.

Step 3: Set the megger to the compressor applicable voltage rating. If the megger you are using only has a few specific voltage ranges, select the next highest voltage above your compressor volt range.

Step 4: Connect one lead of the megger to the copper suction line or housing. Connect the other lead to one of the compressor terminal pins (winding).

Step 5: Repeat the procedure for the two remaining terminal pins. If the instrument indicates any resis- tance less than 2 megohms between any pin and the housing (copper suction line), a ground fault exists. Replace compressor.

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