RLC-SVX07A-EN 89
Operating Principles
the outside air temperature sensor, the saturated condensing refrigerant
temperature sensor, and the saturated evaporator refrigerant temperature
sensor are monitored to determine fan staging.
The number of fans activated at startup is dependant upon the outdoor air
temperature. Figure 38 shows fan activation at different temperatures.
During normal operation, the micro uses PID control to maintain a 70±5 psid
between the condensing pressure and the evaporator pressure. Through the
use of algorithm logic, a fan will be added if the pressure differential is greater
than 75 psid and the fan inverter is at maximum speed.
A “Low Differential Pressure” diagnostic will take the circuit off-line if the
pressure differential falls below 40 psid for more than two minutes.
A “High Differential Pressure” diagnostic will take the circuit off-line if the
pressure differential increases to 350 psid or greater. This diagnostic can also
be produced if the pressure differential increases to the range between 320
psid and 349 psid. The UCM will allow the unit to remain on-line if there is no
increase in pressure for a one hour period. Otherwise, the unit will trip off-line
and display the “High Differential Pressure” diagnostic.
Note: Closest fan to the control panel on each circuit is controlled with the optional fan inverter.
Table 24 Standard RTCA Fan Configuration
Circuit #1 = Right side facing control panel.
Circuit #2 = Left side facing control panel.
To n s Circuit #1 Circuit #2
70 4 4
80 4 4
90 4 4
100 5 5
110 5 5
125 5 5
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