Why wont the the a/c fans wont turn on - 2002 Cadillac Deville

Is the fan relay getting power and a signal from the engine computer ?

replace The Fan motor

I would disconnect the fan connector and use contact cleaner to clean the connection. Usually corrosion. Also fan might be going bad (Common Problem).

If it's electric fan then the wiring pig tail is bad or the relay is toast had same problem on electric fan and it was just the wiring at conectors was bad try that k

Yes you can do that, it will work great.

Replace the starter, the solenoid cant engage the starter because it is locked up, hence the extreme voltage drop with the fan when you try to start it with the fan on.

HOT WIRE COOLING FAN USING JUMPER WIRES TO BATTERY.IF FAN DONT RUN WHEN HOT WIRED FAN MOTOR BAD NEED REPLACING. IF FAN RUN WHEN HOT WIRED. CHECK COOLING FAN FUSE AND RELAY.IF ALL IS GOOD.YOUR ENGINE COOLANT TEMPERATURE SENSOR NOT WORKING.IT CONTROL COOLING FAN AT SET TEMPERATURE IF SENSOR OPEN OR FAULTY THE COOLING FAN WONT TURN ON.CHECK COOLING FAN WIRES FOR DAMAGE.IF ALL STILL CHECK OUT GOOD HAVE VECHICLE SCANNED FOR PCM FAULT.IF IT FAILS NO COOLING FAN WONT TURN ON.

anthonycatel check your rad cooling fan relay. should be in the fuse compatment.

does anything else stay on it sounds like you have a bad ignition switch

check the fan fuse