GMC Repair: no heat out of vents, gmc sonoma, climate control

Question
Hello, I just purchased a 2001 GMC Sonoma ZR2.  It has the 4.3l V6 engine and automatic transmission.  My problem is this; the heater will not blow hot air.  I am fairly certain it is the coolant valve that allows coolant into the heater core.  One hose into firewall is hot, the other is not.  All of the climate control functions are working.  I can hear the coolant valve turning from one extreme to the other when I turn the temperature knob, but still no heat out the vents.  What is required to get to this valve?
I appreciate your time and help in this matter.


Answer
Hi
There is no valve that llows coolant into the core. Hot coolant passes through it all the time....summer, winter fall.
I would HIGHLY suspect the heater core itself.
Classic symptoms of a faulty core are one hose hot other cold or barely warm.
You CAN, remove the hoses from firewall, and blow LOW PRESSURE air BACKWARDS through the core. (Backflushing) NO MORE THAN 30 psi.
This USUALLLY clears clogs, for a while.
I Hope this helps
Pawl