I have a 2006 Chevy Silverado 1500, 5.3l, and I'm having issues with my heat.

With blower off at idle, hot air comes out of whatever vent or defroster I select. If I drive, the hot level goes down a bit. If I turn blower up at all, it gradually gets cooler. On the highway, say on a cold Thanksgiving morning, it produces no heat.

I've had the coolant flushed twice, changed the heater core as it was leaking(determined by my passenger side carpet being soaked with coolant), and also changed the thermostat, and re-flushed the system.

I was thinking water pump or belt, but I was told if the water pump failed, the whole engine would overheat..

Possible the thermostat is stuck open? I did have some stop leak crud in the system, and one person thinks some of it may be lodged in the thermostat housing. But I don't want to keep throwing parts and money at it.

Someone else said it was the HVAC control unit in the cab, but that seems to function fine, as it does what I tell it to do...it's just pushing more air across the core it gets cool.

I'm thinking to pull the T-Stat and just check it, then top off the system and try again?

To clarify, I also have a manual control unit that has been worked on for the blower motor resistor recall years ago. The fan blower function itself works fine.

Ideas or suggestions?

  • Welcome to Motor Vehicle Maintenance & Repair! Are the controls for your HVAC the manual controls or the auto-temp controls (set a temperature and let the unit do the work)? – Pᴀᴜʟsᴛᴇʀ2 Nov 26 '18 at 15:17
  • Hello. I have the manual control, two zones. It was worked on by GM years ago for a blower motor resistor issue. – Rick Nov 26 '18 at 15:19
  • Sounds like your heat-cool knob is positioned backwards or gone bad – user38183 Nov 27 '18 at 0:59
  • Definitely not the heat-cool knob...that doesn't even make sense.. – Rick Nov 27 '18 at 13:28

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