Per my shop manual, the W124 fuel cooler ONLY works when the A/C is actually turned on & refrigerant is actually circulating.

So in a temperate climate I don't think you need it.

BTW, PermaCool makes a dedicated fuel cooler (air-to-air, a simpler design) for under $30 bucks.

:-) neil
1988 360TE AMG
1993 500E