FieldBench
Lennox codes

Lennox

Limp

Protect

VFD limp / min Hz — fan prove

Drive is running too slow to close the prove switch, so the unit board reports fan fail. Reliatel example: Fan Fail with the drive still at min Hz.

Walk Limp in Diagnose

2 plates — walk the one on the cabinet

First check

1 Read the drive before you cycle power

On Lennox LGH photograph the VFD keypad or the unit-board fan alarm (OC, LU, OU, GF, OH, limp). Power-cycle wipes what you needed. Min-frequency / limp parameter vs the prove-switch setpoint (often ~0.07" on some Reliatel cabinets).

Expect: Live drive code written down. Line voltage at L1/L2/L3 of the drive.

The rest of the walkthrough is Diagnose.

On the plates

  • Min-frequency / limp parameter vs the prove-switch setpoint (often ~0.07" on some Reliatel cabinets).
  • A dirty filter that drops the motor into current-limit limp will never make prove. Clean first.
  • Do not jumper the prove switch. Heat will fire into a near-dead blower.

Plates that use Limp

Same number, other makers

Limp on Lennox is not the same code on these plates.