Friedrich racservmn Thermal Overload External, Winding Test, Checking Compressor Efficiency

COMPONENTS:

OPERATION & TESTING

WARNING

DISCONNECT ELECTRICAL POWER TO

UNIT BEFORE SERVICING OR TESTING

COMPRESSORS

Compressors are single phase, 115 or 230/208 volt, depending on the model unit. 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.

WINDING TEST

Remove compressor terminal box cover and disconnect wires from terminals. Using an ohmmeter, check continuity across the following: (See Figure 1)

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.

Figure 1

GROUND TEST

Use an ohmmeter set on its highest scale. Touch one lead to the compressor body (clean point of contact as a good con- nection is a must) and the other probe in turn to each com- pressor terminal (see Figure 2.) If a reading is obtained, the compressor is grounded and must be replaced.

Figure 2

Typical Ground Test

CHECKING COMPRESSOR EFFICIENCY

The reason for compressor inefficiency is normally due to broken 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 gauges to the high and low sides of the system.

3.Start the system and 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 coil

The compressor valves are faulty - replace the compressor.

THERMAL OVERLOAD (External)

Some compressors are equipped with an external overload which is located in the compressor terminal box adjacent to the compressor body (See Figure 3.)

The overload is wired in series with the common motor terminal. The overload senses both major amperage and compressor temperature. High motor temperature or amperage heats the disc causing it to open and break the circuit to the common motor terminal.

Figure 3- External Overload

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