Coleman DGAA056BDTA Error Code 3 Flashes: Combustion Air Pressure Switch Failed to Close

What Does Code 3 Flashes Mean?

A 3-flash code on the Coleman DGAA056BDTA's Integrated Ignition Control means the combustion air pressure switch failed to close after the inducer motor started. At the start of each cycle the inducer spins up to pull combustion air through the heat exchanger and out the vent; the resulting negative pressure should close the switch, telling the board that venting is established. If the switch never closes within the expected window, the control aborts before opening the gas valve, and no burners light.

Because this furnace is a single-stage, mobile-home unit that typically vents straight up through the roof, the most common causes are a blocked vent pipe (ice in winter, leaves, or bird and insect nests at the termination) and a broken or disconnected pressure-switch hose that can no longer sense the inducer's draft. A weakening inducer motor that cannot generate enough negative pressure, or a failed pressure switch, can produce the same result.

This code is the counterpart to the 2-flash fault on the same board. Where 2 flashes means the switch is stuck closed when it should be open at rest, 3 flashes means the switch stays open when it should have closed — describing them by their own definitions is important because they call for very different repairs.

What You'll Notice

• You hear the inducer motor start and run, but the burners never light and no heat follows
• The green LED behind the blower-door view port flashes three times, pauses about two seconds, then repeats
• The furnace tries again on the next thermostat call but keeps failing at the same point
• The problem shows up in cold or snowy weather, when ice can form at the roof vent termination
• Supply registers blow cool air or nothing while the thermostat still calls for heat

Common Causes

How This Is Diagnosed

A technician confirms the inducer actually runs, then measures the negative pressure it develops with a manometer and compares it to the switch's rated closing point. If draft is adequate but the switch does not close, the switch is faulty and is replaced; if draft is low, they look upstream for the cause. That means inspecting the vent run and outdoor termination for blockage, checking the small rubber pressure-switch hose for cracks, kinks, or disconnection, and evaluating the inducer motor and wheel for wear or debris.

The checks proceed from the most common and least invasive outward: venting and hose first, then the switch, then the inducer, since a blocked vent or a fallen-off hose is both more likely and far cheaper to correct than a motor.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• The outdoor vent termination looks clear but the 3-flash code persists
• The inducer motor sounds weak, rattles, hums without spinning, or does not start
• The pressure-switch hose is intact and connected but the switch still will not close
• The vent run is unusually long or has several elbows and the furnace short-cycles on this code
• Ice repeatedly forms at the vent and blocks it during cold weather

✓ Verified against manufacturer service manual — March 2026