When I use air conditioning in my 1995 S350 it runs hotter than normal. I have noticed that my aux fans don't stay on for long at all.... which leads me to believe that there is something wrong with my fan relay. Anybody know WHERE this relay is physically located? A cursory glance under the hood leaves me clueless. Knowing how Mercedes can put things in strange places, I thought I'd ask those who might already know!
Also... any comments/info on similar running hot with AC on would be appreciated.

Are you on your original fan clutch? In addition, you may want to clean 13 years of accumulation from the radiator and condenser fins.

There are two fans and neither of them run for long enough to do much of anything. When I drive down the freeway or in other non-stop situations the temp is fine. So... I am still needing to know the location of said relay.

If you have actually cleaned the radiator and condenser fins and you know that your fan clutch is in good shape, about the only thing left is the radiator itself. It could be lined with calcium inside, preventing enough heat transfer when the conditions get tough.

As for the auxiliary fans, check the temperature of the refrigerant at the switch to see if there is even demand.

Matt... thanks for taking the time to respond, but what I am telling you is... that the fans both come on, but not for long... radiator is FINE. Do you know where the fan relay is located or not?

No, I do not know where the relay is, or even if you have a relay. I know that my car does not have an auxiliary fan relay, but it's a newer body design; yours probably does have one.

I can tell you this, though. The auxiliary fan should start and run if the AC is on and you're idling in place in hot weather. If it does not, one of two things are wrong. The obvious thing is the electrical circuit. The less obvious thing is the cryogenics system. If you are low on refrigerant, your high-side temperature will be much lower and the auxiliary fan will not run for long. If you have a restriction at the condenser or dryer, the temperature at that sensor/switch will be artificially low, but may spike occasionally as liquid gets through.

Thanks for the input. It DOES have a relay. I have a new one right in front of me. I just need to know where to look for the old one.

If you have a part number, you should be able to find it in the EPC. The picture may give you a decent idea of where to find the part.

If you're in the US, EPC access is free. www.startekinfo.com.

Access to EPCnet is included at no additional cost with a subscription to STAR TekInfo, and is also available separately at nominal cost. Please visit http://epc.startekinfo.com for more information.

That nominal cost is 0 if you're in the US. $12 for world cars:

365 Days - FREE - NA Passenger Car

Go and sign up.

I believe the 95 S350 has a couple of pre-resistors nestled between the fans. Make sure there is continuity acorss each pre-resistor.

Sixto
87 300D

The aux fan relay is located at position E or F/G in the rear of the fuse box.

Someone posed a good question???

Does your car have 2 white ceramic resistors between the aux fans? IF not...that can be the problem.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

F & G on my 1995 S350 W140.

Remove the long relay looking thing from the back,top of the outside of the fuse box. It is just in the way.

Remove the 4 black screw on the corners of the fuse box and lift the whole cover off. (The screws do not actually come out. They just back out and disengage from the base.

In the back of the box you will see one pink relay, two baby blue relays, then one long black relay. (Left to right.) The long black relay is the Aux Fan Relay. (Or at least it looks just like the one on Fast Lane )

-Jim

__________________
1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.