Teledyne manual 6712FR Refrigerated Sampler Maintenance

6712FR Refrigerated Sampler

Section 8 Maintenance

The ambient air sensor samples the air temperature outside the refrigerator. It is located in the temperature assembly located on the right of the refrigerator grille. If the ambient temperature is cold, three heaters will be turned on by the circuitry.

Two of the heaters are located on the sides of the evaporator plate inside the refrigerator and one heater is located on the com- pressor.

The fuse, F2, is included on the supply side of the heaters to prevent an electrical hazard in the event of a fault in either heater. Refer to Appendix D Replacement Parts List for replacement fuse part numbers.

The heaters prevent the sample from freezing when the outside air temperature falls below freezing. The compressor will cycle approximately the same amount of times at cold temperatures as at room temperatures.

The ambient air temperature signal comes from the sensor into the circuit board. The signal is then sent to an oscillator. Depending on the temperature, the voltage will vary. This varies the duty cycle of the oscillator, which in turn, varies the duty cycle of the heaters. This circuitry is linear; at 65•F the heaters will begin to come on and at -35•F the heaters will be on continu- ously. When the heaters are on, the internal heat LED indicator will be lit.

The internal temperature sensor is a thermistor that samples the internal air temperature of the refrigerator. It is mounted at the top of the refrigerator’s interior. The internal temperature signal comes from the sensor, through the plug in the ther- mostat/wiring housing assembly, and into the board. The setting on the temperature control knob comes from the potentiometer, through the plug in the thermostat/wiring housing assembly and into the board. If the interior of the refrigerator is warmer than the temperature control potentiometer setting, the internal tem- perature LED indicator will be lit. The temperature control potentiometer is located in the thermostat/wiring housing assembly.

The evaporator temperature sensor is mounted on the front of the evaporator plate. The signal from the sensor comes through the connector in the thermostat/wiring housing assembly and into the circuit board. The evaporator temperature LED indi- cator will be lit if the evaporator temperature is warm (and all the frost has been melted).

The operation of the compressor and the compressor run LED indicator is determined by the temperature control potenti- ometer setting, the internal refrigerator temperature, and the evaporator temperature.

It is not recommended that the user attempt any cali- bration adjustments.

Below is the operation of a compressor cycle assuming that the compressor is already running.

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