81 Low stage thermal lockout

What the control is telling you

Amber STATUS light flashes 81: the compressor thermal protector tripped in low stage three cycles in a row; low stage is locked out for 4 hours or until 24 V is cycled.

Applies to: Carrier 25HNB6/25HNB9 two-stage HP

Likely causes

• Compressor internal overload repeatedly tripping
• Start relay/capacitor staying in circuit too long
• Low voltage, poor airflow or charge problem

Test and repair steps

1. Check line voltage under load.
2. Check the start assist parts and compressor windings.
3. Check charge and airflow, then reset by cycling 24 V.

Models that show this code

8 models in Carrier 2-stage 24ANB/25HNB

Other codes on the same units

• 47 No 230 V at unit
• 53 Outdoor air temperature sensor fault
• 55 Outdoor coil temperature sensor fault
• 56 OAT / coil thermistor out of range
• 71 Compressor dropped out
• 73 Contactor shorted
• 83 Low pressure lockout (4 hours)
• 84 High pressure lockout (4 hours)