How to connect an A419 Digital Temperature Controller from Johnson Controls

The Johnson Controls A419 electronic temperature control units operate single stage heating or cooling systems designed for the control of HVAC or cooling systems. The A419 is available in 24 volt or 120/240 volt configurations. The control unit has an LCD screen for setting and displaying the temperature. It allows a temperature adjustment in the range of -30 to 212 degrees Fahrenheit (-34 to 100 degrees Celsius). Other features include a touch lock, adjustable cut and cut temperature settings, and prevention of short cycle delays. Connecting the A419 requires knowledge of HVAC or the cooling system it will control.

Sensor and switch wiring

Step 1

Turn off the heating or cooling circuit breaker. Remove the four screws in the four corners of the front of the unit using the screwdriver. Separate the front of the unit from the back to expose the wiring terminals.

Step 2

Loosen the terminal screws + Bin, -Com and + Sen in terminal block 3, labeled TB3. Connect one cable of the temperature sensor to the -Com terminal and the other to the + Sen terminal. Connect the shielded cable to the -Com terminal on the long connectors of the temperature sensors. Adjust the + Sen terminal.

Step 3

Connects a binary input switch cable, if used, to the + Bin terminal. Connect the other switch cable to the -Com terminal. Set the terminal + BIN and the -Com.

Step 4

Complete the wiring for the 24, 120 and 240 volt loads as shown in the following sections. Replace the front of the unit on the back and adjust the screws.

24 volt wiring

Step 1

Loosen the two terminal screws of terminal block 1 (labeled TB1) and terminals C and NO in terminal block 2 (labeled TB2), using the screwdriver. Cut a 4-inch (10 cm) long piece of 12-gauge wire and cut a 1/2 inch (1.2 cm) of insulation from both ends. Cut 1/2 inch (1.2 cm) of insulation from both wires from the 24-volt transformer and both 24-volt load cables.

Step 2

Insert a cable from the 12-volt transformer and one end of the 4-inch (10 cm) cable into terminal 2 (marked as T2) in terminal block 1. Set the terminal screw T2. Insert the other end of the 4-inch (10 cm) cable into terminal C of terminal block 2. Adjust the terminal screw.

Step 3

Place a 24-volt charging cable in terminal NO on terminal block 2. Tighten the terminal screw. Place the other 24-volt charging cable, as well as the other 24-volt transformer, in terminal T1 of terminal block 1. Set the terminal screw T1.

120/240 volt wiring

Step 1

Loosen Com AC and terminal 240 or 120 (depending on the voltage) in the terminal block. Loosen terminals C and NO on terminal block 2. Cut a 4-inch (10 cm) piece of 12-gauge wire and cut 1/2 inch (1.2 cm) of insulation from both ends. Strip the ends of the two 120 or 240 volt source wires and the two 120 or 240 volt load wires.

Step 2

Perform this step for 120 volt wiring only. Insert the neutral white wire from the 120 volt source and the white wire from the 120 volt AC load into the COM terminal and adjust the terminal screw. Insert the black wire from the 120-volt source and one end of the 4-inch (10 cm) wire into terminal 120 of terminal block 1. Tighten the terminal screw.

Step 3

Perform this step for 240 volt wiring only. Insert any of the cables from the 240 volt source and any 240 volt load cable into the AC Com terminal, then adjust the AC Com terminal. Insert the 4-inch (10 cm) cable and the other cable from the 240-volt source into terminal 240 and tighten terminal 240.

Step 4

Insert the free end of the 4-inch (10 cm) cable into terminal C of terminal block 2 and adjust the screw of terminal C. Insert the load wire into the other terminal NO into terminal block 2 and tighten the screw of the terminal NO.

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