Location of heater control valve - 2001 Chevrolet Silverado 1500

Car has 4 engines and one diesel , post your engine.
some (many) have no such thing.
if doing DIY,
go to alldata dot com and read. its all there.

on most cars its a flap that covers the heater coil an the coolant runs full time. not saying yours is, as

my 04 has a valve,
its is a vacuum operated valve.
here is the preamble in the above stated links.

1. Drain the cooling system.
   
2. Remove the access panel nut near the pollen filter.
   
3. Remove the access panel.
   
4. Remove the following components from the hot water flow control valve:
   
   • The vacuum hose
     
   • The remaining hose clamps
     
   • The remaining hoses
     
5. Remove the hot water flow control valve.