90 k .... A/C outlets alternates from cooling to heating ... A/C switch light remains ON ...while blowing full heat ... reseting the switch starts the process over ( cool to hot ... no consistency for cycling time ... sometimes, cold all day ..sometimes 5 minutes or less. ) A/C switch? ... compressor problem ? .... advice? .

Either a problem with the blend air motor, or the in-car temp sensor.

The in-car temp sensor is par of the Lo/High range switch.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Thanks .... I have personally maintained a 1973 450 SL since 1975 and a 86 300 SDL since 1987 ...I have the CD's and the manuels ... However,, I'm totally clueless regarding the 99 ML ... How would I find or recognize the low/high range switch???
Thanks again .... Ed