High speed fans not working, low speed work ok

[dammad]

My 99 C2 Cab has begun to overheat slight (right hand of 180) on hot days. I've checked all the threads and can confirm:

- low speed fans come on when AC is pressed

- fuses (row C 8 and 10) both fine (I don't think the low speeds would work either in this case)

- durametric can drive the low speed fans

- durametric "RPM stage 2" which is right under low speed fans (I believe high speed fans) does nothing

- I've removed both the low speed relays and the high speed fans do not pulse on and off as they should do.

- If I feel the high speed relays with the low speed relays out, I don't feel any clicking

So it seems that the relays of the high speed fans aren't getting energised. What else can I test to narrow it down?

[dammad]

Is there a fuse that governs just the high-speed fans?

I'm tempted to try to jumped the high speed fan itself into the output of the low speed fan relay, does this seem like a reasonable test?

[Richard Hamilton]

The high and low speed relays share their main supply. There are two separate signals from the DME (one for each relay) for high and low speed. I think I would check that the relays are getting the signal for high speed. The attached might help.