Hi there.

First time poster as I am a new Mercedes owner. We just got my wife a 1998 ML 320 and it just recently started randomly blowing hot air and then cold air (a/c). It switches back and forth in no apparent pattern. I think the a/c and heater are working fine as the cold is quite cold and the hot is hot, so it seems like there is a sensor or switch that is out of whack. Any ideas would be helpful

Thanks, Mike

That system uses a blend air system. Possibly the controller for the blend air motor is causing that.

Are there any "clacking" noises behind the dash?

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Thanks for your reply.

Come to think of it, we did here clacking noises a couple of times. What does that mean?

Almost always related to the blend air MOTOR not moving the flap correctly.

__________________
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

It was the blended air motor. Part was cheap, labor was expensive. Cost me $720 to get it fixed. Thanks for the input.

Mike