Green ON / Red OFF High pressure lockout

What the control is telling you

The high pressure switch tripped 5 times (5 strikes) and the control locked out the compressor.

Applies to: Lennox EL16KP1 (Elite) and ML14KP1 (Merit) R-454B heat pumps, sizes -018 to -060, demand defrost control A108 (CMC1)

Likely causes

• Restricted airflow over the indoor or outdoor coil (dirty coil, filter, blocked fan)
• Wrong refrigerant charge
• Wrong metering device installed or expansion valve not working properly
• Pressure switch or sensor mounted wrong or loose connection

Test and repair steps

1. Clean the outdoor coil and make sure the outdoor fan runs at the right speed and current.
2. In heating, check indoor airflow (dirty filter, closed registers, blower speed) - the indoor coil is the condenser.
3. Check the charge with the subcooling method; an overcharge raises head pressure.
4. Compare operating pressures with the Normal Operating Pressures table for the unit size.
5. Confirm the correct indoor expansion valve is installed and working.
6. Check the high pressure switch (S4, opens at 590 +/- 15 psig) wiring at HS-PS; make sure pressure switches and sensors are tight on the system.
7. To clear a 5-strike lockout after the repair, place a jumper on the TEST pins (P1) or cycle 24 VAC power to the defrost control; then put the jumper back on the desired setting.

Settings for these units

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