I had a problem with my blower not working properly, so I changed the blower motor. Money spent for no reason I found out. I did realize that if the power is in Aux mode, it works fine. Turn it on so the engine runs,,,nothing. After it ran for awhile and frustration, I hit the top of the dash with my fist and it worked great. I turned it off and back on and the same problem was back. I have only been able to get it to work by hitting the dash one more time. My mechanic thinks it may be the temp sensor, but have no idea where to look to change it.

Any ideas?