A/C troubleshooting

I have a 1991 Cherokee that I recently purchased. When I bought it the A/C and heat worked fine. After power washing the engine area the a/c and blower no longer work. The fan clutch does not engage and the blower does not work for heat or cooling. I have checked the fuse and have checked the blower motor, both are OK. Can anyone direct me to a step by step troubleshooting guide for a/c issues? I have a feeling it is a bag switch or relay but do not know where to begin or how to test.

Alan