80
IMM AGS-2
4.
Add sufficient charge to clear the conditions listed above under “Indications of a low
refrigerant R-134a charge”.
5.
Overcharging of refrigerant will raise the condenser pressure and increase the
condenser subcooling.
Standard Controls
NOTE: A complete explanation of the MicroTech II controller and unit operation is contained
in the Operation Manual OM AGS.
Thermistor sensors
Evaporator leaving water temperature
- This sensor is located on the evaporator water
outlet connection and is used for capacity control of the chiller and low water temperature
freeze protection.
Evaporator entering water temperature
- This sensor is located on the evaporator water
inlet connection and is used for monitoring purposes and return water temperature reset
control.
Evaporator pressure transducer circuit #1, 2
- This sensor is located on the suction side
of the compressor (evaporator outlet) and is used to determine saturated suction refrigerant
pressure and temperature. It also provides low pressure freeze protection.
Condenser pressure transducer circuit
#1, 2
- the sensor is located in the discharge line
and is used to read discharge pressure and saturated refrigerant temperature (calculated).
The transducer will signal the controller to hold load or unload the compressor if a rise in
head pressure occurs which is outside the MicroTech II controller setpoint limits. The
signal is also used in the calculation of discharge superheat.
Liquid pressure transducer #1, 2
– located on the liquid line ahead of the EXV. It is used
to determine liquid pressure and subcooling and is used to control the EXV.
Outside air
- This sensor is located on the back of the control box. It measures the outside
air temperature, is used to determine if low ambient start logic is necessary, and can be the
reference for low ambient temperature lockout.
Suction temperature circuit #1, 2
- The sensor is located in a well on the suction line.
The purpose of the sensor is to measure refrigerant temperature and superheat.
Discharge line temperature circuit #1, 2
- The sensor is located in a well on the discharge
line. It measures the refrigerant temperature and is used to calculate discharge superheat.
Demand limit
- This requires a field connection of a 4-20 milliamp DC signal from an
external source such as a building automation system. It will determine the maximum
number of cooling stages that can be energized.
Evaporator water temperature reset
- This requires a 4-20 milliamp DC signal from a
building automation system or temperature transmitter to reset the leaving chilled water
setpoint.
High condenser pressure control
MicroTech II control is equipped with high pressure transducers on each refrigerant circuit.
The main purpose of the high pressure transducer is to maintain proper head pressure
control. It also sends a signal to the MicroTech II control to unload the compressor in the
event of an excessive rise in discharge pressure to 275 psig (1896 kPa). Also, MicroTech II
control will inhibit additional circuit loading at 267 psig (1841 kPa). The high pressure
switch trip setting is 282 psig (1944 kPa). The high pressure alarm is in response to the
signal sent by the pressure transducer.
