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no heat on 2001 GMC Sierra 1500

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why is there not much heat coming through the vents of 2001 c3 ? There is plenty air moving through but very little heat. How do I fix this problem?
(3) Answers
Backflush heater core, cut both hoses going to core install 2flush kits. Get at walmart Hook garden hose 2 heater out hose leave in hose open, use low pressure and watch junk come out
Please see the RepairPal article regarding the no heat condition of your 2001 GMC Sierra 1500: http://repairpal.com/i-have-no-heat-what-could-be-wrong. While this article applies to vehicles in general you may find some information that will help you find the cause of you problem.
This maybe or may not be the answer but my heater was not putting out heat at idle but did while driving The fan was blowing fine except no heat.Problem was My coolant was low because I had a coolant leak, Fixed the leak added coolant and now heater works great!! Good luck Folks!!!