Bryant air conditioner outdoor unit does not start; control board shows code 34 indicating low-voltage control circuit fault or open contactor coil circuit.

Safety first: Turn off power to both indoor and outdoor units. Low-voltage (24V) can still cause damage or short circuits if mishandled.

Diagnostic steps:

• 1. Check indoor control board fuse: Open the furnace or air handler panel and locate the 3–5A blade fuse on the Bryant control board. If blown, replace with the same rating. If it blows again immediately, there is a short in the low-voltage wiring or outdoor coil.
• 2. Inspect thermostat wiring: At the outdoor unit, inspect the low-voltage cable entering the cabinet. Look for cuts from weed trimmers, rodent damage, or loose wire nuts. Repair any damaged sections and ensure connections to the contactor coil are tight.
• 3. Test contactor coil (visual/basic): With power off, inspect the contactor for burnt or melted plastic. If the coil area is charred or the contactor hums loudly when energized (when power is restored), it is likely failing and should be replaced.
• 4. Verify thermostat call: At the indoor control board, confirm that the Y terminal is energized when cooling is requested. If not, the thermostat or its wiring may be faulty.
• 5. Reset system: After correcting wiring or replacing the fuse, restore power and test. If code 34 persists, the contactor coil or control board may need replacement by a professional.

Note: Do not upsize the low-voltage fuse; this can damage the Bryant control board.