It's always a good practice to disconnect the battery when dealing with electric components. Some models require plugging in a device to the cig. lighter to keep the "system" alive. In your case I think just having the radio code handy is sufficient.

My focus is usually the W126 chassis. The fans you refer to are controlled by a temp sensor. And are activated when engine heat reaches a preset level. The fan on myW126 does not activate with the AC unless the temp sensor has already received a signal to do so. All sensors on my W126 are less than a year old. So I trust their reliability.

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Selling used Mercedes parts on Ebay...always changing...
cdplayer51 take a look!
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