16
Systems and Controls
Model 430
Setting Temperature
1. Position the thermistor fine adjustment at
mid-range. This will limit the fine adjustment
temperature range to ±2_F. (±1_C.).
2. Turn the coarse adjustment clockwise to the
coldest setting.
3. With the freezer correctly primed, place the
power switch in the “AUTO” position.
4. After the appropriate freezing time, test the
product temperature. When a sample portion
temperature is approximately 1_ above the
desired temperature setting, slowly turn the
coarse adjustment counterclockwise (warmer)
until the refrigeration system cycles off.
5. Allow the refrigeration system to cycle through
at least two “OFF” cycles. After the unit cycles
off, draw a sample of product and check the
temperature. Readjust the coarse adjustment
as required, but make only small adjustments.
Note: The anticipator automatically activates the
refrigeration system 0 - 1 second after the draw valve
is opened. If several small samples are drawn, the
temperature may drift lower. To accurately set the
control, let the product temperature stabilize by
allowing the thermistor control to cycle the freezer on
and off by the control set point instead of the
anticipator.
Service Tips
If a problem arises with the thermistor control
assembly, identify and replace only the faulty
component. For example, if the probe is defective,
replace only the probe.
A varistor must be connected to the thermistor
control’s 24 VAC terminals in order to protect the
control from voltage spikes (varistor part number
X31547).
Fill the bulb-well with automotive antifreeze before
installing the thermistor probe, and be sure the probe
is installed completely into the bottom of the bulb-well.
Note: Lower the probe to the point where the wires
extend from the probe and a resistance is felt. This
indicates the probe is installed completely in the
bottom of the bulb-well.
If the thermistor relay which starts the compressor will
not close, check the following items:
ELECTRICAL SHOCK AREA! USE CAUTION!
1. Make sure power is being supplied to the
freezer and that all operating switches are in
the correct position.
2. Using a voltmeter, check the voltage supply to
the thermistor control. The control requires 24
volts to operate.
3. Using an ohmmeter, check probe resistance.
(Refer to the thermistor curve chart on page 17
for proper readings.)
If the thermistor relay which deactivates the
compressor will not open, check the following items:
ELECTRICAL SHOCK AREA! USE CAUTION!
1. Make sure the thermistor relay opens when the
freezer control switch is in the “OFF” position.
2. Make sure the thermistor probe is connected to
the correct probe terminals.
3. Using an ohmmeter, check the thermistor probe
for proper resistance. (Refer to the thermistor
curve chart on page 17 for proper readings.)
4. Disconnect one wire to an anticipator terminal.
If the thermistor relay opens after
approximately 25 seconds, the problem is in the
anticipator wiring circuit.
When problems such as erratic product quality occur,
it is of utmost importance to determine if the thermistor
components are defective before replacing them.
For a diagram of the thermistor control, see
page 27 (Troubleshooting Thermistor
Components).
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