E429 Inverter DC link low voltage (inverter code 23)

What the control is telling you

On a compressor call the DC link did not rise above 180 VDC (2- and 3-ton) or 250 VDC (4- and 5-ton) within 30 seconds; unit stops. 10 times in 60 minutes = lockout. Inverter LED flash code 23 (red 2 flashes, green 3 flashes). S30/S40 thermostat alert code 429 (shown as E429 on the unit control display).

Applies to: Lennox communicating heat pumps incl. variable-capacity inverter units in S30/S40 smart thermostat systems

Likely causes

• Low input voltage
• Loose U/V/W connections
• Failed inverter, filter board or reactor
• Compressor winding or ground fault

Test and repair steps

1. Run the thermostat's test function (S30: Dealer Control Center > Tests) and read the inverter's DC link plus line input voltage and current.
2. Check U, V, W connections at the inverter harness and compressor.
3. Check compressor winding resistance and compressor to ground; replace compressor if bad.
4. Check input power single phase 208/230 VAC +10%.
5. Before you change the inverter, test what is feeding the filter board and reactor.
6. Measure the DC link and MICOM sensing voltage. Out of range: replace the inverter. In range: the compressor likely has a mechanical problem.
7. Clears automatically once fixed.
8. Check inverter LEDs flash code 23 = red 2 flashes, green 3 flashes. Normal inverter LEDs with no fault: red ON, green OFF.

Settings for these units

• Outdoor unit clearances · Lennox EL16KP1
• Outdoor unit clearances · Lennox ML14KP1