W115 heater and A/C blower both died when I pulled cluster
 

Hello,

I have a '76 300D (W115 chassis) that needed a speedometer oiling and a odometer fix. Did this with no problem, but then I reinstalled the cluster and found that:

• The blowers for both A/C and heat are inoperative.
• The A/C compressor does not engage when I switch the blower on and turn the temperature knob all the way clockwise.
• The A/C and heater both worked well before this, and all the climate controls were functional.

I also was doing other work in my engine bay too, so perhaps it was something in the fire wall, but I doubt it. I pulled both of the panels under the steering column for this job, so I could have hit something under there, too.

Any tips on this before I get started, to save time? I feel like I could spend hours trying to diagnose this issue.

Thank you for the help !
Henry C.

Any blown fuses?

I'd second the fuse Check them closely the other is the back plug on the fan motor and the plug to the temp wheel. They may have come dislodged

The changeover switch is physically attached or connected to the driver's-side lever next to the console, just above the accelerator pedal. It is electromechanical and snaps into position to feed either the blower fan for heat or the squirrel-cage blower for A/C.

It's conceivable that the linkage may need adjustment to ensure that the switch goes through the required arc to engage the A/C or heater fans--or the switch may be in the middle position, with both fans disengaged. The relays for the compressor and other high-draw components are on the passenger-side cabin behind the glove compartment. I've found these to be very reliable.

The fuses on the firewall are for power windows and the supplementary fan but Mercedes sometimes used 16-amp fuses there for other optional equipment. They are prone to oxidation and frequently open the circuit even though they look fine. It does sound like the changeover circuit is malfunctioning--good luck



Tim Kraakevik
kraakevik@voyager.net

Thanks for the tips, everyone.

Nailed it. I managed to break the two rivets holding the switch to a metal brace-- replaced them with 4 cm M3 screws to fix it. I found that the heater actually was working, and it was stuck in the heat mode. I didn't really understand the climate system until this--new car -- but found that the heater is so quiet that I didn't notice it was stuck on. Probably a good thing that it runs quietly given how hard it is to fix.

Henry C.