should Aux fans run all the time with A/C on?
 

my 1990 300E has no cooling. When I turn the dial to full cold, and switch to auto, shouldnt the auxilary fans run? Even if the compressor is bad, or I am low on Freon? Mine dont turn on. Im just wondering if this is the problem. My condensor isnt disipating the heat cuz of the fans not running. Thanks

check the fuse for the fans in my 190E (m103 engine) the fuses were melted and wouldnt let the fans engage.

to check the freon level...located the dryer
this guy, mine is moutned behind the driver's side headlamp
[IMG]http://www.***************/secure/PartImages/1248300283Z.jpg[/IMG]

there is a little watch glass on the top of it..clean it off and run the AC. my one mechanic said "if you see bubbling/foaming then it could use a recharge"....

good luck

The low speed fan will come one when it thinks it has to. (this would be when the pressure builds up, due to compression and lack of heat dissipation through the condenser)

should the aux fans run
 

the way benz designed the fans they don't run with ignition or a/c on unless high pressure in a/c above 250psi[approx] now i always wire the cars that i see so that when compressor on fans on [i don't think that they tested the cars in dallas in august.] your situation implies that[1] not enough refrig in system [2]fuse blown [3] fans faulty [4] sensor on drier bad [5] relay bad or[6] broken wiring.

Simple Low Fan test .

Jumper pigtail wires going to drier/reciever high pressure switch.. if fan runs , you have verified the fans electricals [ motor/relay/fuse/resistor/etc]
This indicates you do not have enough high side pressure to trigger the fan high pressure switch.. most common probable would be low on refrigerant.
There is also the remote possible of having a bad switch, but very few fail this test.
Also remember , as LD posted, that the fan will not come on until it is called for .. meaning the system/switch has detected a HIGH THERMAL LOAD CONDITION... usually due to high ambient temp/humidity. The aux fan is only designed to relieve the high pressure when the system is being TAXED,, in cooler ambient temp, it is quite common to have stisfactory a/c output without the high side needing aux fan inputs b/c the high side does not get to the sw cut-in spec and is therefor unneeded.
A truer test is to use gauges for switch spec comparisons, but those who know these systems well can test fan operation in 30 seconds with a simple jumper wire and observation of the high side Eye-Sight Glass..

Thanks guys, I did the site glass suggestion first, and it is bubbling. I am assuming I am low on freon. I can feel the compressor kick in, and I am getting some cooling, but when its above 75 F, it doesnt work at all. It has been fairly cool the last couple of days, but also humid. Maybe a combination of this and low refr. I will do a pressure test. The guy I bought the car from said it was converted to the new r132, but he didnt change the filter/drier. Would it be a good idea to completely evac, and fill with a new drier?

Yes, it would. The oils used in the two refrigerants are different types, and hate each other. Why was it changed in the first place? Flush it, flush it again, check for leaks, and refill with R-12.

Well it has the new service valves for the r132, and I thought for one, they dont sell r12 anymore, and two, its illegal to use this.

FYI
R12 is Licensed and r132 is not a refrigerant replacement, but R134a is.

What Arthur is saying by "licensed", it means "Johnny on the street" can't have r12, you need to go through a class and get certified to use it now, can't just go buy those little cans of r12 any more. If you are buying a little can of refrigerant, it's not R12 or it's illegal.
You should also have a conversion label on the car over or near the original AC information sticker listing when the conversion was done and by whom, and how much R134 was put in.
Gilly

Thanks Gilly. Good explaination .........
The point being , of course, is R12 is still a viable Rerigerant, so his statement of it not being sold anymore and illegal are both incorrect.
That is a common misconception, which is why I used the FYI format for my post.
..many of us can remember buying the R12 cans off the shelf at discount stores for .88 cents a can... but there again, I owned a Service Station that charged 28.9 for regular and customer would come in a say "Give me $1 worth , would ya? " .. we would answer " Sure , ...ya Goin' on a Trip ?? "

:):)