Carrier 59SC5A Error Code Continuous OFF: No Power
What Does Code Continuous OFF Mean?
When the amber LED on your Carrier 59SC5A control board is continuously off, the board is receiving no electrical power. It needs both 115VAC line voltage (at L1 and L2) and 24VAC secondary voltage (at SEC-1 and SEC-2) to function. Without power, the furnace is completely inoperative — it will not respond to thermostat signals or run any cycle.
This is one of the most frequently encountered furnace issues, and the cause is usually simple. A tripped circuit breaker is the most common culprit. The furnace power switch (a standard light switch mounted on or near the unit) may have been accidentally turned off. The Carrier 59SC5A also has a blower door safety switch — if the front panel is not fully seated, this switch cuts power to the control board as a safety measure.
If all these check out and the LED remains dark, the issue may be a failed transformer or an internal board problem. These require professional diagnosis.
Common Causes
How to Fix It: Check Power Supply and Door Safety Switch
What You'll Need
- Flashlight
Steps
- Turn off power at the breaker and shut off the gas supply valve Locate the circuit breaker for your furnace in the electrical panel and flip it to OFF. Find the gas shut-off valve on the gas line leading to the furnace and turn it to the closed position. If you smell gas at any point, leave the house immediately and call your gas company from outside.
- Check the circuit breaker Look at your home's electrical panel. Find the breaker labeled for the furnace or HVAC system. If it is tripped (in the middle position or at OFF), push it firmly to OFF first, then flip it back to ON. Breakers can appear to be on while actually tripped — always reset by pushing fully off first.
- Check the furnace power switch Locate the power switch on or near the furnace. It looks like a standard light switch and is typically mounted on the furnace cabinet or on the wall nearby. Make sure it is in the ON position. This switch is sometimes accidentally turned off during laundry, storage, or cleaning activities near the furnace.
- Verify the blower door is fully engaged The Carrier 59SC5A has a door safety switch that cuts all power to the control board when the blower compartment door is removed or not properly seated. Push the door firmly into place and make sure it is latched. The door must fully depress the safety switch for the board to receive power.
- Restore power and check the LED Turn the gas supply valve back to open, then turn on the breaker. Wait 30 seconds and look through the viewing window on the furnace door. If the amber LED now shows a steady continuous glow, power is restored and the furnace is in normal standby.
When to Call a Professional
Contact a licensed HVAC technician if:
- The breaker trips again immediately after resetting
- The power switch, breaker, and door panel are all correct but the LED remains off
- You notice a burning smell or visible damage near the furnace or electrical panel
- The furnace lost power after a power surge or lightning strike
- You suspect a failed transformer or internal board issue