Cold Mixture Heater - CMH
This system reduces cold engine emissions and improves driveability during engine warm-up. The intake manifold is heated during cold engine operation to accelerate vaporization of liquid fuel.
The ECM checks alternator (terminal L) to determine if engine is running. It also checks engine's coolant temperature. If engine is running and coolant temperature is below 109°F (43°C), ECM energizes CHM (relay) which applies battery voltage to CMH. The CMH is a multi-element heater ring that is mounted between carburetor base and intake manifold. Once coolant temperature exceeds 131°F (55°C), the CMH relay is de-energized and heater elements turn off. See Fig 1 and COLD MIXTURE HEATER OPERATION chart.