Teledyne Refrigerated Sampler 6712FR - Manual (Page 171)

6712FR Refrigerated Sampler
Section 8 Maintenance
8-19
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.