Burried behind the dash on the passenger side, good luck.
The heater core is located on the passinger side under the dash board remove the cover screews and take it from there.Dave K. 1999 Silverado 1500 4WD 5.3 Vortex 8 owner
Short answer is you got to pull the dash, then the HVAC box (contains the core). Replace the core then remember how to put it all back. I am going to try and do it without pulling the whole truck apart, today. If it works. I will tell you how it went.
Probably heater core
4WD - 1999 Window was released on: USA: 1999
4WD - 1999 Friday was released on: USA: 1999
4WD - 1999 Bump was released on: USA: 1999
4WD - 1999 Show was released on: USA: 1999
4WD - 1999 Merge was released on: USA: 1999
4WD - 1999 Flirt was released on: USA: 1999
4WD - 1999 Gym was released on: USA: 1999
4WD - 1999 Coffee was released on: USA: 1999
18,826 lbs.