Mercedes ACCII Blower Only Works on Defrost - Mercedes-Benz Forum
 
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post #1 of 3 (permalink) Old 02-04-2018, 12:26 PM Thread Starter
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Date registered: Oct 2017
Vehicle: 1985 Mercedes 190D, 1980 Mercedes 300SD, 1981 Mercedes 380SL, 1977 Mercedes 450SL 60k miles
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Mercedes ACCII Blower Only Works on Defrost

Good Afternoon-
I have a 1980 380sl with the wonderful ACCII system. My servo had a crack in it, so I replaced it this weekend with the unwired tools electronic upgrade kit.

Before the replacement:
-Heat didn't work, but the blower motor came on for every setting (DEF, Auto Hi/ Low, and Bi-Level).

After the replacement:
-The heater valve does open (because of the kit), but the blower motor only works on the Defrost setting.

I have completely gone through every vacuum line, and I cannot locate any leaks. The new controller is getting 12v power.

I cannot figure out why the blower motor worked on all settings before the install, but now will only come on in Defrost. Any advice would be greatly appreciated. Thanks!
-Davis
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post #2 of 3 (permalink) Old 02-04-2018, 07:21 PM
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Recheck your vacuum system, specifically the little check valves that live behind the brake booster area heading into the cabin.

When these fail they close up and seal the vacuum system. I believe defrost mode is the fail-safe when it goes belly up.
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post #3 of 3 (permalink) Old 02-04-2018, 08:29 PM Thread Starter
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Problem Solved

Okyoureabeast, thanks a bunch for getting back to me! I narrowed the issue down to vacuum switch valve #14 not opening (because of a leak somewhere), and thus not allowing the blower motor to come on. “Defrost” bypasses this vacuum switch valve, so it was able to come on in that mode.

After I spent all day checking the darn vacuum system, I was fed up, so I chose to bypass vacuum switch valve #14.

Now the system works for heat and A/C in all settings as designed with the electronic conversion kit. The only downside is you cannot cut it off. I’ll probably put an electronic toggle switch in the glove box at a later date so my blower motor doesn’t burn up.

For now, better never to cut it off than never to have it on.
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