Which is the switch on the receiver / dryer that controls the aux fans on my '91 300E? There are two switches there, one sticking straight up, and one coming out sideways, both seem to have two poles on them.

I'm trying to diagnose why my aux fans don't come on at the low (fan) speed when my A/C is running. The A/C blows cold, especially going down the road, which may be because I 're-oiled' my fan clutch silicon fluid myself, and the clutch doesn't really release all that easy anymore. (The Toyota fluid came in three different viscosities, I chose the higher viscosity.) I don't mind the main fan running more, as I live in a hot climate. Anyway, maybe the A/C condensor is getting adequate cooling due to the main fan without help from the aux fans, but I'd rather have the aux fans working properly.

Note that the aux fans do activate and run at high speed when the engine temperature reaches 105 degrees C. So this leaves me with 1) faulty pressure switch on the receiver / dryer, or 2) the resister that is bolted to the fender behind the driver's headlight is faulty, or 3) bad connection somewhere on that circuit (though I don't see where).

If it is the pressure switch, can I bypass that switch? I don't want to have to evacuate and re-charge the system just to replace the switch, and the A/C is running acceptably right now.

Thanks,

Jeff

__________________
On the plains of hesitation bleach the bones of countless millions who at the dawn of victory, sat down to wait, and waiting -- died

The one with the wire pigtail leads with spade connectors..
If jumper works, do not ASSUME the sw is bad .. a common mistake.
It can simply mean you are slighly low on refrigerant.

Thanks for the reply! The refrigerant was topped off this week at the dealership, so it isn't that.

Spade connectors... I thought they both had spades... I thought it wasn't the switch sticking straight up, becuase when I disconnedted one of those connectors the compressor clutch disengaged.... or is this the same switch? It has spades.

I'm trying to make sure before I jump anything.

Thanks

__________________
On the plains of hesitation bleach the bones of countless millions who at the dawn of victory, sat down to wait, and waiting -- died

I said spade connectors on a pigtail.
The compressor spades DO NOT have a pigtail..

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1M30LAGSC1V218KLBA&year=1991&make=MB&model=300-E-002&category=R&part=A%2FC+Temp.+Switch

The pressure switch off of the ac goes to a resistor, heater behind the drivers head light back on the right looking down on it. hard to get to. this slow the fan speed down from full speed. This covered by a heat shield. The conections there break from heat.
Start there
Joe

and the switch appears to be faulty. I tested the entire circuit, at the relay contacts, the relay itself, across the resistor, the ground at the switch, jumped the switch contacts, and with the key on the fans now work...

Bad switch right? I just had the system recharged last week, and I can see bubbles go by in the window on the dryer...

Any harm in my leaving the switch bypassed for the rest of the summer? What I think I'll do is remove the bypass in the fall, and probably bypass it again next summer, and keep doing that until I have to recharge the system again, at which time I'll replace the dryer and the switches.

__________________
On the plains of hesitation bleach the bones of countless millions who at the dawn of victory, sat down to wait, and waiting -- died

>>Bad switch right? I just had the system recharged last week, and I can see bubbles go by in the window on the dryer...
>>

The only way to verify pressure switch is with a gauge reading on the high side. Foam/bubbles in quanity at sightglass indicate low refrigerant . Which will not allow the system to reach high side pressure needed to trip aux fan low speed circuit.
Some guys run a cabin sw across the sw so they can regulate the low fan to their liking.
remember , aux fan only comes on at high thermal load, meaning there are time [low ambient temps/low thermal load] , that the fan circuit is not being called for...this is NORMAL...