RT-SVX36G-EN
153
Unit Start Up
On air-cooled units, the expansion valves shipped installed were factory set to control between 14-
18°F at the ARI full load rating conditions (approximately 45°/125°F saturated suction/discharge).
On evaporative condenser units, the expansion valves shipped installed were factory set to control
between 18-22°F at the ARI full load rating conditions (approximately 45°/105°F saturated suction/
discharge). At part load, expect lower superheat. Systems operating with lower superheat could
cause serious compressor damage due to refrigerant floodback.
Tables are based on outdoor ambient between 65° & 105°F, relative humidity above 40 percent.
Measuring the operating pressures can be meaningless outside of these ranges.
Measuring Superheat
1.
Measure the suction pressure at the suction line gauge access port located near the
compressor.
2. Using a Refrigerant/Temperature chart, convert the pressure reading to a corresponding
saturated vapor temperature.
3. Measure the suction line temperature as close to the expansion valve bulb, as possible. Use a
thermocouple type probe for an accurate reading.
4. Subtract the saturated vapor temperature obtained in step 2 from the actual suction line
temperature obtained in step 3. The difference between the two temperatures is known as
“superheat”.
When adjusting superheat, recheck the system subcooling before shutting the system “Off”.
Note:
If unit includes the modulating reheat dehumidification control option, adjust superheat
only in the cooling mode of operation.
Charging by Subcooling
The outdoor ambient temperature must be between 65° and 105° F and the relative humidity of the
air entering the evaporator must be above 40 percent. When the temperatures are outside of these
ranges, measuring the operating pressures can be meaningless.
Do not attempt to charge the system with the low ambient dampers and/or hot gas bypass
operating (if applicable). Disable the low ambient dampers in the “Open” position (refer to the
“Low Ambient Damper” section) and de-energize the hot gas bypass valves before taking
performance measurements.
With the unit operating at “Full Circuit Capacity”, acceptable subcooling range for air-cooled
condenser units is between 14°F to 22°F. For evaporative condenser units, acceptable subcooling
ranges is between 8°F to 14°F.
Note:
If unit includes the modulating reheat dehumidification control option, adjust subcooling
only in the cooling mode of operation.
Measuring Subcooling
1.
At the liquid line service valve, measure the liquid line pressure. Using an R-410A pressure/
temperature chart, convert the pressure reading into the corresponding saturated temperature.
2. Measure the actual liquid line temperature as close to the liquid line service valve as possible.
To ensure an accurate reading, clean the line thoroughly where the temperature sensor will be
attached. After securing the sensor to the line, insulate the sensor and line to isolate it from the
ambient air. Use a thermocouple type probe for an accurate reading.
3. Determine the system subcooling by subtracting the actual liquid line temperature (measured
in step 2) from the saturated liquid temperature (converted in step 1).
