Cooling Fans Won't Run
 

I have a 2002 Montana. Cooling fans won't turn, it is cool enough that if I am moving it will run at the proper temperature. Fuses, all 3 relays are all good the Temperature sensor/ sending unit is ok has approximately the right resistance for the temperature it is at. The sensor is getting 5 volts from the PCM . I can't tell for sure, but the wiring from the fuse box to the PCM appears to be in good shape. The harness has never been disturbed , but does mean a wire isn't broken some where and I just can't see it. I hate wiring issues too. I don't want to spend big dollars on a PCM replacement and re-config. to find out its a wire some where. Any easy tricks of the trade to check continuity? Also the A/C hasn't worked in quite a few years, so I am not sure if the system needs to see pressure when you turn on the A/C or if it just needs to be switched on to get the fans to run. When I turn it to A/C the fans don't run either.
or would it be more advantages to buy a Hayden auxiliary fan control?