So this happened last spring. Heat always blows out of the vents even with temp turned down and ac on. I solved the problem last summer by pinching off the hoses to the heater core but i would like to repair it this year.
Is there a valve in the heater core hose? Or is it something in the circuit board? Any advice would be appreciated.
Carl

 

In most cars, like the S40, there's indeed a valve in the heater hose. If it's not malfunctioning or stuck open, it can keep heat flowing all the time. So, I’d suggest checking and possibly replacing this valve first.
But before doing that, check the whole heating system for any other problems. Look if there are any leaks or blockages in the hoses going to and from the heater. You might need to flush the system to clear out any clogs and make it work well again.
Also, since you mentioned the circuit board, check the HVAC control system for any issues with sensors or glitches that might be causing the heat to stay on. Sometimes, just fixing or replacing a faulty part can solve the problem.