How to Wire a Johnson Controls A419 Digital Temp Controller

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The A419 electronic temperature control units from Johnson Controls operate a single stage heating or cooling systems designed for controlling HVAC or refrigeration systems. The A419 is available in both 24 volt or 120/240 volt configurations. The control unit features an LCD for setup and temperature display. It allows a temperature setting in the range of -30 to 212°F. Other features include a lockable touch-pad, adjustable cut-in and cut-out temperature settings, and anti-short cycle delays. Wiring the A419 requires knowledge of the HVAC or refrigeration system it will control.

Things You'll Need

  • Philips screwdriver
  • Slotted screwdriver
  • 12 gauge wire
  • Wire stripper

Sensor and Switch Wiring

Turn off the circuit breaker to the heating or cooling circuit. Remove the four screws at 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.

Loosen the +Bin, -Com and +Sen terminal screws on the terminal block 3, labeled TB3. Connect one temperature sensor lead to the -Com terminal and the other to the +Sen terminal. Connect the cable shield to the -Com terminal on long lead temperature sensors. Tighten the +Sen terminal.

Connect one lead of the binary input switch, if it used, to the +Bin terminal. Connect the other switch lead to the -Com terminal. Tighten the +BIN terminal and the -Com terminal.

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

24 Volt Wiring

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

Insert one lead from the 12 volt transformer and one end of the 4-inch wire into terminal 2 (labeled T2) on terminal block 1. Tighten the T2 terminal screw. Insert the other end of the 4-inch wire into the C terminal on terminal block 2. Tighten the terminal screw.

Place one wire from the 24 volt load into the NO terminal on terminal block 2. Tighten the terminal screw. Place the other wire from the 24 volt load, as well as the other 24 volt transformer wire, into the T1 terminal on terminal block 1. Tighten the T1 terminal screw.

120/240 Volt Wiring

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

Perform this step for 120 volt wiring only. Insert the white neutral wire from the 120 volt supply and the white wire from the 120 volt load into the AC COM terminal and tighten the terminal screw. Insert the black wire from the 120 volt supply and one end of the 4-inch wire into the 120 terminal on terminal block 1. Tighten the terminal screw.

Perform this step for 240 volt wiring only. Insert either wire from the 240 volt supply and either wire from the 240 volt load into the AC Com terminal, then tighten the AC Com terminal. Insert the 4-inch wire and the other wire from the 240 volt supply into the 240 terminal and tighten the 240 terminal.

Insert the free end of the 4-inch wire into the C terminal on terminal block 2 and tighten the C terminal screw. Insert the other load wire in the NO terminal on terminal block 2 and tighten the NO terminal screw.

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