Can’t Stop Climate control for 87’300E

Hi,everyone,

My MB is 87 300E. The climate control system can't be stoped.

I pressed the "O" , the climate system fan just stop for couple sec. then it runs again. If I hold the button "O", the system can be stoped.

But I can't press the button for the whole trip.

Can anyone here help me out those questions?

1   what singal the switch send out?  cut off the circuit off or send out the "1"   singal?

2 Where is the control relay located?

3 Does anyone have this kind of experience?

Thanks for any words here!

All the best.

Peter