Friedrich SH20L30-B, SH15L30-B manual Component Operation and Testing, Compressors, Ground Test

COMPONENT OPERATION AND TESTING

WARNING

DISCONNECT ELECTRICAL POWER TO THE

UNIT BEFORE SERVICING OR TESTING

COMPRESSORS

Compressors are single phase, 208/230 volt. All compressor motors are permanent split capacitor type, using only a running capacitor across the start and run terminal.

All compressors are internally spring mounted and externally mounted on rubber isolators.

Line Voltage Overload

The compressor is equipped with an internal line voltage over- load. This overload is embedded in the windings of the motor to sense the motor temperature. The overload will open and disconnect the power to the motor due to high temperatures caused by:

1.A locked rotor.

2.Excessive running amps.

3.High discharge temperature.

4.Low refrigerant charge.

FIGURE 1 INTERNAL OVERLOAD

LINE BREAK

INTERNAL OVERLOAD

OHMMETER

COMPRESSOR WINDING TEST (Figure 2.)

Remove the compressor terminal box cover and disconnect the wires from the terminals. Using an ohmmeter, check continuity across the following:

FIGURE 2 COMPRESSOR WINDING TEST

Testing Procedures

1.Terminal "C" and "S" – no continuity – open winding

–replace compressor.

2.Terminal "C" and "R" – no continuity – open winding

–replace compressor.

3.Terminal "R" and "S" – no continuity – open winding

-replace compressor.

4.Terminal "C" and the shell of the compressor – continuity

–grounded motor – replace compressor.

5.Should continuity exist between terminals "R" and "S", but not between terminals "C" and "S" and "C" and "R", the internal overload may be open. If the compressor is extremely hot, allow it sufficient time to cool. It may require as long as one hour for the compressor to cool sufficiently for the internal overload to close.

GROUND TEST

Use an ohmmeter set on its highest scale. Touch one lead to the compressor body (clean point of contact, as a good connec- tion is a must) and the other probe in turn to each compressor terminal. (See Figure 3.) If a reading is obtained, the compressor is grounded and must be replaced.

FIGURE 3 TYPICAL GROUND TEST

CHECKING COMPRESSOR EFFICIENCY

The reason for compressor inefficiency is normally due to bro- ken or damaged suction and/or discharge valves, reducing the ability of the compressor to pump refrigerant gas.

This condition can be checked as follows:

1.Install a piercing valve on the suction and discharge or liquid process tube.

2.Attach gages to the high and low sides of the system.

3.Start the system. Run a "cooling or heating performance test."

If test shows:

A.Below normal high side pressure.

B.Above normal low side pressure.

C.Low temperature difference across the coil.

The compressor valves are faulty - replace the compressor.

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