Lennox Error Code 433 (E433): Inverter Compressor Over-Current (Meaning, Causes, Fixes)

What the code means

Lennox's inverter outdoor units (for example the SL25KCV and other variable-capacity models with a Lennox communicating thermostat) report alert 433 as "OD Inverter Compressor Over-current." Lennox's alert code guide and the SL25KCV Unit Information say the error occurs when the compressor's peak phase current is greater than 28 amps. The inverter issues code 14 first (thermostat alert 441, a compressor slowdown for high current) and slows the compressor to bring the current down. If the current stays high, the outdoor unit stops the compressor and fan, starts its anti-short-cycle timer, and posts 433 as a Service Soon alert. If it happens five times within 60 minutes, the system locks out and the alert becomes Service Urgent. Lennox notes there's a six-minute delay at initial startup to prevent nuisance alarms, and that 433 can also be raised by the Lennox outdoor control itself (not the inverter) when the inverter slows the compressor below its minimum speed, typically at startup. If 433 appears but the inverter's LEDs aren't flashing code 29 (red two flashes, green nine flashes), it came from the outdoor control. Normal inverter LEDs are red on steady and green off.

Likely causes

• Compressor peak phase current above 28 amps, which the inverter can't bring down by slowing the compressor (Lennox's definition)
• The system running at high pressures; Lennox lists this as the likely issue behind the code 441 slowdown that comes before 433
• Older Lennox outdoor control software (before version 1.27) raising 433 at startup when the inverter slows the compressor below its minimum speed
• General HVAC background, not from Lennox's 433 entry: anything that raises head pressure, such as a dirty or blocked outdoor coil or a stalled outdoor fan, makes the compressor draw more current

Safe DIY checks

1. Check the thermostat's notifications and note whether 433 is alone or paired with 441 (compressor slowdown for high current) or high-pressure alerts. Write all of them down for the technician.
2. Reset the way Lennox describes: turn off power to both the indoor unit (furnace or air handler, which supplies 24 VAC to the outdoor control) and the outdoor unit, then turn power back on and restart the system.
3. With the outdoor power off, look at the outdoor unit. Clear leaves, grass clippings and debris from around the coil, and make sure nothing is blocking airflow on any side or above the fan.
4. If the outdoor coil is visibly dirty, rinse it gently from the inside out with a garden hose (power off), or use a no-rinse coil cleaner. Don't use a pressure washer, which bends the fins.
5. If your system is connected to the internet, make sure software auto-update is enabled in the thermostat. Lennox says outdoor control software 1.27 and later adds a start-up delay (six minutes in cooling, 11 in heating) that stops 433 from tripping at startup.
6. If 433 keeps coming back, especially with a lockout, stop resetting it and call a Lennox dealer. Repeated over-current trips point to pressures, wiring, the inverter, or the compressor, and the inverter section holds high voltage.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• 292 Lennox HVAC System 292
• 31 Lennox HVAC System 31
• 413 Lennox HVAC System 413
• 434 Lennox HVAC System 434
• 178 Carrier HVAC System 178

All Lennox codes →

Sources

1. Lennox Residential Communicating Systems Alert Code Guide (V2, 100017), Table 2: 433 OD Inverter Compressor Over-current, 28 A peak phase current, inverter code 14 then 29, five times in 60 minutes lockout, outdoor control software 1.27 start-up delay, 17D27 control, reset steps
2. Lennox Unit Information SL25KCV (Corp. 100102), outdoor control alert code tables: E433 / inverter code 29 compressor over-current, five times within an hour lockout, clearing by cycling indoor (24 VAC) power; E441 high-pressure note