34.2 Flame lost before blower on-delay

What the control is telling you

Flame was proven after ignition but then lost before the heating blower on-delay ended.

Applies to: Carrier 59SC6A

Likely causes

• Dirty flame sensor
• Gas pressure drop after valve opens
• Vent or combustion air problem
• Poor ground

Test and repair steps

1. Warning: Turn off gas and power and lock out before removing burner parts.
2. Clean the flame sensor with 0000 steel wool only (no sandpaper or emery cloth); check it sits in the flame.
3. Verify ground continuity green/yellow wire to gas valve and manifold bracket screw, and the flame-sense ground wire to furnace sheet metal.
4. Check natural gas supply (4.5-14 in. w.c.) while burning and manifold pressure (2.8-3.8 in. w.c. for 40k-120k models; max 1.8 in. w.c. on 26k).
5. Inspect burners and orifices for dirt or blockage; clean burner with brush and vacuum.
6. Inspect vent and combustion-air pipes for water, sags or blockage.
7. Run 2 complete heat cycles and look at the flame: it should be clear blue, almost transparent.

Settings for these units

• Filter sizes by casing width and filter cabinet · 59SC6A
• Minimum clearances to combustibles · 59SC6A