233484 Suburban LIMIT SW – L77 – NT20SQ – (YELLOW)

The 233484 Suburban Limit Switch – L77 – NT20SQ (Yellow) NT-12 16 20S is the OEM auto‑reset high‑limit switch used in Suburban NT20SQ furnaces. It protects the furnace from overheating by opening the circuit when the heat exchanger reaches its rated temperature limit. Once temperatures drop back into the safe range, the switch automatically resets and allows the furnace to resume normal operation. Your product page confirms the part number, color, and compatibility, along with the list of OEM replacement numbers.

Replaces: A31023, 230621, 230635, 233020, 233021, 233022

Function and Role in the Furnace

This limit switch is part of the furnace’s safety chain. It:

• Monitors heat exchanger temperature

• Opens the circuit if temperatures exceed the L77°F limit rating

• Automatically resets when temperatures fall

• Prevents overheating, short‑cycling, and heat‑exchanger damage

• Works with the sail switch, ignition board, and thermostat to maintain safe operation

A failing limit switch often causes intermittent heating, furnace shutdowns, or blower‑only operation.

Key Features

• OEM Suburban auto‑reset limit switch

• Temperature rating: L77

• Designed for NT20SQ furnaces

• Yellow identification for correct model matching

• Direct‑fit replacement with OEM wiring and mounting

• Restores proper furnace safety and cycling behavior