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CAUTION
Minimum compressor superheat of 20°F may override these recommendations on systems with short line runs.
The condensing unit must have the discharge pressure above the equivalent 105°F condensing pressure (reference
refrigerant charging on page 16).
CAUTION
Correct location and full contact of the expansion valve bulb is extremely important for proper system performance.
Johnson Control A421 Electronic Temperature Control
• The front panel of the A421 Series Electronic Temperature Control has an LCD and a three-button UI
LCD
• The A421 Series Control has a backlit LCD screen. You can adjust the LCD brightness. During normal operation, the
LCD displays the Main screen, which provides the following information:
• Temperature sensed at the A99 sensor
• Selected temperature units (°F or °C)
• Mode of operation (Flame = Heating mode, Snowflake = Cooling mode)
• Binary Input status (BIN) when a user-supplied binary input (switch) is connected and closed to enable the
temperature setback feature.
• During setup and adjustment, the LCD displays the parameter code screens and the parameter value screens. See the
A421 Control parameter setup menus for more information.
Three-button touchpad
• The touchpad has three buttons for setup and adjustment of the A421 Control. See Navigating the Basic and Advanced
menus for more information about the three-button touchpad.
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