Low speed fan comes on with A/C speed below 43 mph or if engine temp reaches 215F.
High speed fan comes on if temp reaches 230F and low speed fan has been running.
The fan speed is determined by the computer which triggers the hi or low speed fan relay located in the box under the radiator shroud.
I may be wrong ... but I don't think this cooling system uses a dropping resistor. From my recollection, there are two sets of windings on the fan that are triggered from either the Hi speed relay (K3) or the Lo speed relay (K4).
Count the number of electrical connections on the fan housing .... 3 wires means two sets of windings.
I agree with SHOZ123. You are suppose to have 2 sets of windings. Both provided 12V to the fan. No resistor.
I also suggest jumping both legs of the fan(independently). It's possible one of the windings is busted.
Side note. I just hacked a '93 Escort 2 speed fan, into a '91 Vulcan (1 speed) Taurus. These fans do not "spin up" They Turn ON. Get ready for voltage surge.
My fan does indeed have two sets of windings, and the fan is working at both speeds, depending on which winding I apply voltage to.
My system appears to be working correctly.
What I was hearing was actually the fan on low speed. It cycles on and off on low speed, never running on high. I think that is because sufficient cooling is achieved on low speed (there is never an inkling that the engine is running too warm, even in hot weather). That surprises me somewhat, as most of my driving is stop and go city type driving. However, I rarely use the A/C. If I did, perhaps that would impose a thermal load great enough to trigger a high speed fan condition.
My other car's fan switches switches speeds quite readily and I think that's why I thought there was a fault with this one.
Thanks for the help guys... I learned something here!