Cooling fans come on when Engine cold
 

I've got a 1991 Mercedes 420SEL -- most of the time the electric cooling fans roar to life upon engine startup (cold), then turn off about 5 minutes later (after engine warms up). Other than that, they DO operate normally at elevated engine temp's (when idling hot day and a/c/ turned on -- water temp gauge is up there..).

What's going on here?

I'd appreciate any input...

Bob Irving
Charlotte, NC

Hi Bob,
my '87 420 also had the electric fan running this morning when I stopped after about a minute to pick up the paper. I assume various temp. and pressure switches do their job. I had the car at an AC specialist after I bought it about 2 years ago and they tested when (at what pressure) the electric fan came on and found everything ok. As the AC works and temp is max at 100 in stop and go, otherwise around 85, I leave it alone.
Hope this helped.
Reinhard Kreutzer

I had a similar problem with my E420 and it turned out to be the blue two prong temp switch part number
008-542-45-17

RKreutzer,
Were the fans running on high speed and was the A/C switched off? If so you have the same problem.
It is not normal operation.

Replacing the switch is a 5 min job.

See this thread: http://www.peachparts.com/shopforum/showthread.php?threadid=7301

Chris

Hi Chris,
the AC was on. I only hear the electric fan when I get out of the car and pass the front with engine running. It is not always on but with the high 80's now in the morning, I assume the pressure is building rather quickly and it asks for the electric fan. It did this since I own it and I had it checked (see above). But I'll keep an eye on it.
Thanks again
Reinhard

Reinhard,

I believe your aux fan is working as designed. In high temp conditions the aux fan will come on low speed soon after turning on the a/c and will stay on while idling. The switch on the a/c drier controls this. You also have a temp switch on the engine which turns the aux fan on high speed at 100c.

Chris

Thats what I thought
Thanks again
Reinhard

Thank you Reinhard and Chris for your replies and thoughts on the cooling fan problem. I appreciate it.

Regards,

Bob Irving