FieldBench
Carrier codes

Carrier

31 / 42

Lockout

Pressure / inducer band

Modulating inducer did not hit the pressure band for the commanded firing rate. Not a discrete two-stage PS.

Walk 31 / 42 in Diagnose

Sign in for the next measurement

First check

1 Prove inducer and the live code

Do not pull power — that clears the Carrier 59MN7 active code. Write 31 / 42. Is the inducer spinning on this call? Silent inducer is not a pressure switch. Vent, trap, inducer, pressure transducer/hose — there may not be two discrete PS like 59TN6 or 59TP6.

Expect: 120 VAC at the inducer on a heat call. Wheel turning.

If fail: 120 VAC missing → IFC / door switch / incoming power. Voltage + dead motor → inducer.

If pass: Inducer running + this code → trap, hose, switch, vent (step 2).

The rest of the walkthrough is Diagnose.

On the plates

  • Vent, trap, inducer, pressure transducer/hose — there may not be two discrete PS like 59TN6 or 59TP6.
  • Do not ohm a ‘low’ and a ‘high’ switch that are not there.
  • Attic PVC and collector still drown a modulator. Band miss + wet collector is still a trap call.
  • 42 = inducer RPM out of the band the IFC commanded.

Plates that use 31 / 42

Same number, other makers

31 / 42 on Carrier is not the same code on these plates.