Lennox Error Code 413 (E413): High Pressure Switch Strikes Lockout (Meaning, Causes, Fixes)

What the code means

Lennox outdoor units have a high pressure switch (called S4 in Lennox service literature) that opens when refrigerant pressure gets too high and closes again once it drops. Lennox's Unit Information for the SL25KCV gives the switch settings as open at 590 psig and close at 418 psig. Each time the switch opens, the compressor stops and alert 412 (OD Open High Pressure Switch) is logged; that one clears on its own once the switch closes. The control counts these trips, and when the switch has opened five times within a single thermostat demand, it raises alert 413 (OD High Pressure Switch Strikes Lockout), shuts the outdoor unit down and keeps it off. Lennox's alert code guide lists 413 as Service Urgent. The SL25KCV literature says the lockout is reset by cycling the 24 VAC power to the outdoor control, which comes from the indoor unit, or by putting the outdoor control in test mode. In short, 412 is one high-pressure trip and 413 means it kept happening.

Likely causes

• Dirt, leaves, grass or debris blocking airflow through the outdoor coil (Lennox says to confirm the outdoor unit is clean)
• The outdoor (condenser) fan motor not running or running poorly
• Wrong refrigerant charge; Lennox says to check the charge using superheat and subcooling
• A clogged expansion valve (TXV) or clogged refrigerant filter drier
• A blocked or failed indoor blower, a dirty filter, or indoor airflow set too low (Lennox notes low indoor CFM in heating and low zone CFM on zoned systems)
• A stuck reversing valve on a heat pump

Safe DIY checks

1. Look at the thermostat's alert list. If you also see 412 entries, those are the individual high-pressure trips that led to the 413 lockout.
2. Turn the system off at the thermostat, then switch off the outdoor disconnect before going near the unit.
3. Clear leaves, grass clippings, cottonwood fluff and anything stacked against or on top of the outdoor unit so air can flow freely through the coil and out the top fan.
4. If the outdoor coil fins are visibly matted with dirt, rinse them gently with a garden hose or use a coil cleaner made for condenser coils. Don't use a pressure washer or bend the fins.
5. Replace or clean the indoor air filter and make sure supply and return vents aren't closed or blocked, since poor indoor airflow can drive high pressure in heating mode.
6. Reset the lockout the way Lennox describes: turn power off to the indoor unit (the furnace or air handler switch or breaker, which supplies 24 VAC to the outdoor control) and back on. Turn the outdoor disconnect back on too.
7. Start a cooling or heating call and watch the outdoor unit. If the top fan isn't spinning while the compressor runs, shut it off and call a technician. A fan that won't run will keep tripping the high pressure switch.
8. If 413 comes back after cleaning and a reset, the cause is likely charge, a restriction, a reversing valve or the fan motor, which need gauges and a technician.

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
• 433 Lennox HVAC System 433
• 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 p.30: 412 OD Open High Pressure Switch and 413 OD High Pressure Switch Strikes Lockout (Service Urgent, five strikes, check charge, outdoor fan, debris, reset)
2. Lennox Unit Information SL25KCV (Corp. 100102): E412/E413 table (open 590 psig, close 418 psig, causes, reset by indoor power) and Figure 24 High Pressure Switch (S4) sequence of operation