2000 Chevy Silverado 1500 The heater does not

Question edited for clarity and typo, and add maker.
Question moved to model category.

The AC evaporator core and the heating core are normally two separate items. It is unlikely that the heater core is completely clogged. There must be a valve in your flushing circuit.

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The AC compressor will come on when you turn on the defroster. If you're not getting heat it's most likely that your heater core is going bad. You can flush it out and see if it's getting clogged. Also check your water pump to make sure you have enough flow through the core. The reasoning behind the ac blowing when the defroster is on is that it blows dryer air on the windshield.

flush the heater core.

Purchase a new mode selector switch for it at any Chevy dealerships parts department

once truck is warm check both heater core hoses to make sure they are both warm if not then check the cold water valve could be stuck shut not allowing coolant to travel in to heater core.

try back flushing heater core, they often plug up, use garden hose remove hoses from heater core and flush water through it going both ways a couple of times start there. good luck.

The air ducts need to warm up ...much like adjusting the water for a shower.

For your 2nd question..it's just the nature of the beast.

Hope this helps you

I had the same problem that I just fix by flushing the heater core out with a hose.   take the two hoses off the fire wall and put the water to it and let flush.  my heater is putting out 150 dg. F  of hot air.   I'm so excited!  i will stay warm now.

the problem is caused by the motor that operates the air temp blend door motor in the heating ducts, it blends air between AC and heater core tro give desired outlet temp.

i had the same problem with my 2000 chevy truck!! i took both hoses off engine and flushed the heater core with water and air frome air compresser,added new coolent and it works perfect!!!! so try flushing your system............