I HAVE A 2003 RAM 2500 HO AND I HAVE A PROBLEM WITH MY AC. THE PROBLEM HAS HAPPENED TWO TIMES IN THE LAST MONTH. I CAN GET IN, START THE TRUCK, AND TURN ON THE AC OR HEATER AND IT COMES ON AND THEN THE FAN SHUTS OFF COMPLETELY. THE ONLY THE LEFT ON IS THE AC LIGHT. YOU CAN TURN ALL THE ***** AND NOTHING HAPPENS. BUT WHEN I SHUT THE TRUCK COMPLETELY OFF THEN RESTART IT EVERYTHING WORKS FINE.
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PLEASE HELP IF YOU CAN THANK YOU

PS PULLED CODES AND THERE WERENT ANY IN MEMORY.

 

First thing I would check is for a loose connector on the back side of the HVAC controls.
Remove the screw under the hanger on the dash and the center dash cover should pop right off.

MikeyB

 

I had one do something similar one time and it was the ignition switch. Does everything else stay on? You might try wiggling the ignition switch, just be careful and don't engage starter.