J
Very Good

just wanted make you aware of the relay/fuse difference , as it is a common confusing point on these systems .
..and you will see the relays swapped sometimes , adding more confusion..
[that usually happens when someone suspects a bad reay and does a swap for testing purposes]
The basic thing one wants to remember is:
HIGH FAN is for engine temp [ and triggered by the ECT sensor on the engine]
LOW FAN is for a/c system [ and triggered by the high pressure sw on the a/c drier]

Each has it's own relay and fuse , and each is an entirely seperate system.
If one has no high fan, he does not go looking into the low fan circuit and vica/versa..
Another tip for any readers of this post:
The fuse on the blue relay that always seems to blow has been upgraded by Benz to a 25Amp, as thay found the 15 was not sufficient , specially when they came out with the dual fan set-up... So, if one has no LOW fan , one of the first palces to look is at this 15A fuse , as it is the most common electrical fault on NO low Fan complaint. The other would be a pressure problem with low refrigerant charge being the culprit [ not reaching adequate HIGH side pressure to trip low fan].
A simple jumper of the high P/SW. is a good diagnostic trick here as with the jumper, if the fan does not come on , the fuse is suspect, but if the fan then starts , low refrig. is suspect.... [ or a remotely possible bad high pressure sw. ]