Hmmm. I don't know if an altimeter will tell you anything about your radiator fan. Where do you get an altimeter anyway, instrument panel of a small plane?

Try this... Take the plug off of your fan switch. It's the sensor in your thermostat housing. With the ignition on (I don't know if the engine actually has to be running), short the 2 wires together. That should make the fan turn on. If that works, then you know your fuses, wiring, relays, and fan motor are all OK.