Thermistor Control - Taylor 430 Service Manual

Thermistor Control

Function
The thermistor control maintains temperature in the
freezing cylinder by monitoring the resistance of the
thermistor probe.
Specifications
Temperature Differential:
above cut-out.
Coarse Adjustment Range: 10_ to 30_F. (-12_ to
-1_C.).
Fine Adjustment Range: 4_F. (2_C.) total.
Coarse Adjustment Potentiometer:
approximately 6_F. (3_C.).
Input Voltage Supply: 24 VAC.
Thermistor Probe (Part # 038061-BLK)
The resistance value of the thermistor probe
corresponds with the product temperature in the
freezing cylinder. As the product becomes colder, the
probe resistance increases. As the product becomes
warmer, the probe resistance decreases.
Approximate probe resistance readings:
1. 10,000 ohms at room temperature:
78_F. (25_C.).
2. 46.012 ohms at serving temperature:
20_F. (-6.6_C.).
Operation
The thermistor probe is positioned in the bulb-well
located at the front of the freezing cylinder. The
thermistor control becomes
powered by the 24 VAC transformer.
When the desired product is achieved (control
set−point) the thermistor control relay opens and
discontinues the power sent to the compressor relay
coil.
Model 430
cut in = 2_F. (1.1_C.)
1/4 turn =
operational when
When the product in the freezing cylinder reaches 2_F.
(1_C.) above the control set-point, the thermistor relay
closes, sending L1 power to the compressor relay coil.
The refrigeration system will run until the control
set-point is achieved.
Anticipator
The anticipator signals the thermistor control to
activate the refrigeration system whenever product is
drawn. As the draw valve is raised (freezer draw switch
closes), continuity is created between the thermistor
control anticipator terminals. The thermistor control
relay will close within 1 second to start the refrigeration
system.
Upon completing the draw, the thermistor control
recognizes the loss of continuity between the
anticipator terminals, but will continue refrigeration for
at least 25 seconds. This allows for additional blending
and freezing of the warmer mix which has entered the
freezing cylinder. After approximately 25 seconds
have elapsed, the thermistor control returns to normal
operation and cycles off the refrigeration system when
the set-point temperature is achieved.
Cycle Timer
During periods when no product is being dispensed, an
8 minute cycle timer will signal the thermistor control
to activate the refrigeration system. As the timer
cycles, continuity is created between the thermistor
control anticipator terminal. The thermistor control
relay will close within 1 second. The refrigeration
system will then activate.
15
Systems and Controls