Bussmann THL Thermal Heat Limiter Fuse (NOS, Boxed) — GM #6556440 Replacement

Description:

The limiter assembly is stamped:

MICROTEMP 139C — PATENTED — FP13 — 3V4238A — Terminals: C / S / B

The box identifies:

Buss THL — Replacement for GM #6556440 — Thermal Heat Limiter Fuse

Key Specs

• Brand: Bussmann (GM supplier)

• Model: THL

• GM Replacement Number: 6556440

• Temperature Rating: 139°C cutoff

• Terminals: C (Compressor), S (Switch), B (Battery/Power)

• Function: Protects A/C compressor clutch circuit from overheating

• Era: 1960s–1980s GM factory A/C systems

• Use Case: Over‑temperature protection for Frigidaire A6 compressor harness

This limiter opens the circuit if the compressor clutch or wiring overheats — preventing harness melt or compressor damage.

🚗 Correct GM Applications

This THL limiter fits nearly all GM vehicles equipped with the Frigidaire A6 compressor, including:

GM Cars

• Chevrolet: Camaro, Chevelle, Nova, Impala, Caprice

• Pontiac: Firebird, LeMans, Grand Prix

• Buick: Skylark, Riviera, Electra

• Oldsmobile: Cutlass, Delta 88, 98

• Cadillac: DeVille, Fleetwood

GM Trucks

• Chevy C/K series

• Suburban

• Blazer

• GMC Sierra / Jimmy

Why It Matters

• Required for OEM‑correct A/C restoration

• Often missing or bypassed on old vehicles

• NOS units are increasingly rare

• Essential for concours builds and high‑value restorations