Have 2004 suburban 1500 heat does not work for rear. Auto will be at operating temp heat from dash is hot but rear is cold. Any suggestions?

AFTER YOUR TRUCK IS AT OPERATING TEMP CHECK BOTH OF THE HEATER HOSES GOING INTO THE REAR HEATER AND SEE IF ONE IS HOT AND THE OTHER ONE IS COLD. IF THEY ARE AS I MENTIONED THEN YOUR PROBLEM COULD BE THE REAR HEATER CONTROL VALVE (if the valve is located after where you checked the hoses) OR YOU HAVE A PLUGGED HEATER CORE AND IT NEEDS TO BE FLUSHED OR REPLACED. IF BOTH HOSES ARE COLD THEN CHECK WHERE THE REAR HEATER CONTROL VALVE IS LOCATED AND IF IT IS BEFORE THE REAR HEATER HOSES START THEN SEE IF THE HOSE GOING INTO THE REAR HEATER CONTROL VALVE IS HOT GOING IN AND COLD GOING OUT AND IF IT IS REPLACE THE VALVE AND THAT WILL FIX YOUR REAR HEATING PROBLEMS ! GOOD LUCK ! MICHAEL...