heater issues

i have a 92 Z-71 that has heater issues. it works fine with the blower on low and med. but when you flip it to high it will run for about five minutes and then the whole thing shuts down. the display goes to totally off and stays that way for about 5 min. then it will power back up on its own back to the med. setting. i changed the 3 relay things behind the glove box and still not cured the thing. any ideas what could be causing this?

cmon guys somebodys gotta have a idea whats causing this.

Swap the control unit - what the hell, worth a shot

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