Ok, when I put the slider to Hot on my car, cold air blows out. I checked the water valve (which I had replaced with a new GM one a few years ago), and the plunger definitely works when the slider is moved from Hot to Cold and vise versa. I checked the hose from the valve to the heater core along the firewall, and the hose gets hot, so it looks like the valve definitely works. Also, I can hear the shudder door move when the slider is moved, so I dont think theres a problem with the door or the blower motor..
Any idea what it can be? Could it be that the water valve went bad again? Heater core? Low coolant?
Any idea what it can be? Could it be that the water valve went bad again? Heater core? Low coolant?