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Old 09-12-2003, 10:40 AM
jcyuhn jcyuhn is offline
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Join Date: Jun 2000
Location: Plano, TX
Posts: 2,476
Odd Problem: 124 fan resistor

Hi All - Was wondering if anyone has seen a problem like this before? On my new-to-me 1993 300E, one of the very few problems I identified was the aux fans not running at low speed when the a/c was switched on. It was relatively easy to trace this to the dropping resistor. One of the two wires to it was disconnected. Not on purpose, mind you, but it appeared to have overheated and burned off. The spade connector was still bolted to the resistor, but the wire had detached. The wire itself didn't look so good - the insulation was a bit charcoal-like, and the copper was greenish - looked overheated.

I cleaned things up, crimped on a new lug, and put it all back together. Worked beatifully - fans came on low after a few seconds at idle with a/c, coolant temperature never exceeded 90C, even on the hottest days.

That was early in the summer. Fast forward, and it's happened again. I noticed the coolant temp was reaching 100C in cool weather. (I should note 90F is "cool" here.) Sure enough, same problem. Both times it has been the wire on the 'supply' side, as opposed to the 'fan' side of the dropping resistor. I repaired it again last night. This time I ohmed out the resistor - 1.9 ohms, which as I recall is about right.

Anyone seen this before? Any thoughts on the matter? The hot wire seems awfully small to supply two fans - it looks to be about 18 guage to my eye. Also, the connecting post on the dropping resistor appears a bit brown and heat damaged. Think I might be getting extra resistance - and extra heat - from this?

It's not a big deal, as a/c season is winding down. However, this is the biggest problem on my new car, so it's all I have to play with!

- JimY
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