The high pressure switch in a Lennox air conditioner serves as a safety mechanism that prevents refrigerant pressure from reaching dangerous levels. If the switch trips, the system stops to protect components. This guide explains why a Lennox AC might trip, how to safely reset the high pressure switch, and what steps to take to restore performance while keeping safety in mind.
Symptoms Of A Tripped High Pressure Switch
Recognizable signs include the outdoor unit failing to start, the system shutting down shortly after starting, or the thermostat showing a fault code related to high pressure. In some models, the outdoor unit will run briefly before shutting off with an error like “HP” or a flashing light pattern indicating a high pressure condition. The issue often presents without obvious external damage, making troubleshooting essential.
Common Causes Of High Pressure Trips
High pressure trips are caused by conditions that raise refrigerant pressure or impede heat transfer. Common culprits include a dirty or clogged condenser coil, blocked airflow from a dirty air filter or obstructed outdoor unit, refrigerant undercharge or overcharge, a faulty thermostat or control board, and outdoor temperatures that are unusually high for the system’s capacity. Regular maintenance reduces the likelihood of trips by keeping components clean and properly charged.
Is It Safe To Reset The High Pressure Switch?
Resetting can be part of a temporary troubleshooting step, but the underlying cause must be addressed. Do not bypass safety features or continually reset the system if the problem persists. Repeated resets can lead to compressor damage or refrigerant leaks. If the unit continues to trip after a reset, seek professional service to diagnose and repair the root cause.
How To Safely Perform A Reset
Note: Always power down the system before inspection. Steps below apply to many Lennox models but may vary by unit. If you’re unsure, contact a licensed HVAC technician.
- Turn off the Lennox outdoor unit at the disconnect switch and at the thermostat to remove power.
- Wait 5–10 minutes to allow pressures to equalize in the refrigerant circuit.
- Restore power at the outdoor disconnect switch, then reset the thermostat if needed.
- If the unit starts and runs normally, monitor for re-tripping. If it trips again, do not attempt repeated resets.
- Inspect visible components: clean or replace a clogged condenser coil, replace dirty air filters, and ensure unobstructed airflow around the outdoor unit.
- Check for obvious refrigerant issues (dye leaks, oily residues) and ensure the refrigerant charge matches manufacturer specifications, but only a licensed technician should adjust refrigerant.
If the high pressure switch has a dedicated reset button on the control enclosure or nearby, press it gently after addressing any obvious airflow or heat transfer problems. Some Lennox models use a control board reset rather than a physical button; follow the owner’s manual for model-specific instructions.
What To Check Before Calling A Technician
- Condenser coil cleanliness: Use a garden hose on a gentle spray to remove dirt; avoid bending fins.
- Airflow: Confirm supply and return vents are open, and outdoor unit has clear clearance around it.
- Air filters: Replace dirty filters to restore proper airflow and heat exchange.
- Outdoor temperature and humid conditions: Extremely hot days can push systems toward high pressure; consider whether the unit is appropriately sized for climate and usage.
When To Call A Professional
- The high pressure switch trips repeatedly after a reset.
- You notice refrigerant oil around connections or a visible refrigerant leak.
- The condenser coil is damaged, corroded, or severely bent fins.
- You suspect an overcharge or undercharge of refrigerant, or the system won’t maintain temperature.
- Electrical components show signs of damage, burning smell, or arcing.
Preventive Tips To Reduce Future Trips
- Schedule annual professional maintenance to clean coils, check refrigerant levels, and test safety switches.
- Keep outdoor unit free from debris, ensure proper clearance, and protect from landscaping growth.
- Replace air filters every 1–3 months depending on usage and indoor air quality.
- Ensure the system is properly sized for the home and climate to prevent overworking the compressor.
- Address airflow restrictions in the home promptly to maintain efficient heat exchange.