Johnson Controls A421ABC-04 Temperature Control

The Johnson Controls A421ABC-04 is a line-voltage, single-stage electronic temperature control designed to provide precise switching for HVACR systems. Operating on 120/240 VAC, this controller features a versatile SPDT output relay that manages heating or cooling applications across a wide temperature control range of -40 to 212?F. As the upgraded successor, the A421ABC-04 is a direct replacement for the A419ABC-3, though technicians should verify terminal labels during field installation. The unit includes a high-accuracy A99BB-400C temperature sensor with a 13.1-foot PVC cable and a 2-inch stainless steel probe, ensuring reliable feedback in demanding environments. Housed in a NEMA 1 enclosure, the controller supports both DIN rail and surface mounting, offering flexibility for control panels or wall-mount setups. Contractors benefit from the LCD front panel, which provides clear status icons and a three-button interface for navigating advanced menus, including adjustable anti-short cycle delays and sensor offset settings to protect compressors and maintain system calibration.

Key Benefits

• Universal voltage compatibility allows the A421ABC-04 to operate on both 120V and 240V circuits without internal jumpers.
• Integrated anti-short cycle delay protects refrigeration compressors from rapid cycling and premature failure.
• Features a backlit LCD screen and an LED status indicator for immediate visual confirmation of relay activation and system parameters.
• Advanced temperature setback and sensor failure modes allow for energy-efficient operation and failsafe protection.
• Standard NEMA 1 (IP20) high-impact thermoplastic enclosure provides robust protection for interior installation on flat surfaces or 35mm DIN rails.

Common Questions

Is the A421ABC-04 compatible with my existing A419 wiring?
While the A421ABC-04 serves as the direct replacement for the A419ABC-3, the terminal positions and labels on the TB1 and TB2 blocks have changed. Technicians must cross-reference the wiring guide to ensure the hot, neutral, and relay leads are landed correctly.

What happens if the A99 temperature sensor fails?
The controller includes a sensor failure mode (SF) that can be programmed to keep the relay energized or de-energized, preventing system damage during a sensor fault.

Can I extend the length of the included 13.1-foot sensor cable?
Yes, the sensor leads can be extended using standard 22 AWG shielded cable. It is recommended to use the sensor offset feature in the menu to calibrate for any resistance changes introduced by additional wire length.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.