Cool Harness is just a resistor wired in parallel with the coolant temp sensor, as macdrone said above, nothing more than that. Are you experiencing this now with cooler weather, or just during the summer heat? As ps2cho said, this doesn't seem like an airflow problem, particularly at this time of year. It's more likely a coolant problem (or bad temp gauge). Has the coolant system been serviced recently? Right coolant mix, correct/working thermostat, no debris between rad and condenser, no pressure leaks, tight reservoir cap, etc.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't