Ok, well my Aux fans do turn on when they hit the appropriate temp which is like 110 or so...Although I just noticed that unless im driving down the highway my A/C does not cool. Obiously its blowing hot air when in stop and go traffic.....so my question is..

Is there a switch i can check or is this something more complicated...The clutch does turn on as a little fyi, and at night my a/c blows cold and does auto control when it reaches the appropriate temp. Any advise?

 

I just went through the same thing. For some reason MB decided that four fuses need to be involved with the A/C fans by using fused relays. The fused relays are located under a cover that is part of the fuse box assembly. You get at them by removing 6 phillips head screws around the perimeter of the fuse box. The relays use the automotive blade style fuses - one is green (30 amp) and one is blue (15 amp). Check all fuses on all of the relays (there are other relays in there that are not A/C related, but I can't remember which is which). If your fans are not coming on, but the A/C otherwise works, this is the likely cause. There is also a 15 amp cartridge style fuse in the fuse box and a 30 amp fusible link style fuse near the battery that are in series with the relays (hence the mystery as to why MB used fused relays) that should be checked as well. Since these fuses have a higher I2t rating (amperes squared * time), the fuses on the relays almost always blow first, but check them all.

You may have a problem with with the fans themselves. This is an easy test. With the car off, spin one of the fans as fast as you can by hand. The other fan should also spin, but slower (the first is acting as a generator thus turning the second one). Do the same to the other fan an look for the same. If they both behave, the fans are good.

You may also have a problem with the high pressure "super heat" switch. This is located on the receiver-drier on the front left side of the engine compartment. There are two pressure switches located there (the other is the low pressure switch that protects the system from refrigerant loss). With the A/C on, jumper each one, one at a time. One should turn on the A/C fans, full speed (assuming the fuses are good). If yes but the fans still don't come on when the A/C is running, it must be replaced.

Hope this helps,

- FD