injected into the evaporator, causing it to cool the circulating fluid. The pulse width of the valve directly controls
the amount of refrigerant injected, thereby affecting the temperature of the fluid. The valve is generally pulsed at
a fixed interval with varying pulse width. When the system requires cooling, the ECB’s DC CONTROL – RLY 6
sources 24 VDC to the sat cool solenoid, causing it to open and inject refrigerant into the evaporator. An LED at RLY
6 also indicates the relay status. When the LED is ON, the valve is energized. Chamber fluid temperature is
measured by temperature probe, Tcl. Chamber temperature is measured by temperature probe, Tc.
6.4.5 EVAPORATORS
The refrigeration evaporators are brazed plate heat exchanger thermally coupling the sat and chamber fluids with
the R134A refrigerant system. One side of each evaporator is connected to the refrigeration system, while the
circulating fluid flows through the other side. As liquid refrigerant is injected into the evaporator, it expands into
gas. This expansion causes cooling (by absorbing heat), which lowers the temperature of the circulating fluid
flowing through the other side.
Saturator fluid flows through one evaporator to cool the saturator. Chamber fluid flows through the other
evaporator to cool the chamber.
6.4.6 REFRIGERATION PRESSURE SENSORS, PRL & PRH
The refrigeration low-side pressure sensor, P
RL
, measures the suction side
pressure of the refrigeration compressor. Readings from this sensor are in
gauge (relative) pressure. The sensor is powered from 12 VDC and has a 1-5
VDC output. The sensor is connected to the ECB at A/D INPUTS – AD1. Power
for the sensor is applied from AD1 12V+ and AD1 GND. The sensor’s voltage
output in the range of 1 to 5 VDC is connected to AD1 SIG.
The refrigeration high-side pressure sensor, P
RH
, measures the discharge side
pressure of the refrigeration compressor. Readings from this sensor are in
gauge (relative) pressure. The sensor is powered from 12 VDC and has a 1-5
VDC output. The sensor is connected to the ECB at A/D INPUTS – AD0. Power
for the sensor is applied from AD0 12V+ and AD0 GND. The sensor’s voltage
output in the range of 1 to 5 VDC is connected to AD0 SIG.
6.4.7 EVAPORATOR BYPASS SOLENOID, SOL 8
The evaporator bypass solenoid, SOL 8, is used to cool the compressor during
times of high demand when cooling from high temperatures to low. It injects
refrigerant directly into the compressor suction line to overcome the heat
removed from the system in an attempt to keep the compressor cool. This valve
is actuated by a 24VDC pulse width modulated signal. When energized, the valve
opens allowing refrigerant to be injected directly into the suction line, cooling the
compressor. The pulse width of the valve directly controls the amount of
refrigerant injected, thereby affecting the temperature of the fluid. The valve is
generally pulsed at a fixed interval with varying pulse width. When the system
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