The three relays can be accessed from under the front of the vehicle near the radiator, there is a 10mm bolt that secures the bracket, it can be slid over and brought down for some access.
Here is a guide to help you test the relays
https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit
Before you go chasing relays, which are fairly uncommon, does the fans come on when A/C is requested? If they do, then they are probably functional. You specify that it uses coolant at an accelerated rate but there is no external leak, that would suggest to me an internal leak. You also specify that it has no head gasket problem, how was this determined? The reason I ask, is that head gasket leaks are probably the most common cause of mysterious coolant consumption and/or overheat, aside from external leak or low coolant. To answer your question, the three relays give both the fans two speeds, low and high. I have included your a schematic, for reference below.
Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.
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Wednesday, March 23rd, 2011 AT 2:30 AM