Poor cooling

When I woke up this morning the frezzer was reading 20 degrees and the refrigerator 50 degrees. after taking off the bach panel I saw that the Condenser fan was not running. I placed a 20 inch box fan near it and shortly afterwards the temps were fine. The condenser fan cost $125 so I want to be sure that I am buying the right part. When I took the condenser fan out I noticed it ran on 11.5 DC volts and it has four wires, red,yellow,blue, white. How do I test it?