I think one or more relays has gone bad in my car, the wipers do not work and the HVAC fan is not blowing. What is the easiest way to test the relays in the fuse box under the hood? Thanks!

 

Can you swap it out with another relay (assuming there is another one...I'm just guessing here) to see if that resolves your problem?

 

The relays should be 12volts, try to get 12v from somewhere and apply to the relay input line, then it should open or close. If not, the relay is most likely faulty.

 

You need a factory service manual for these issues. Follow the diagnostic trees for each problem.

 

There are many different kinds of relays. In order to systematically test one, you have to specifically know how it works internally... or like nbtx said, the manual will specify a diagnostic procedure.

Did you check the fuses?