My heater has been blowing cool air for a while so I decided to check it out. All the flaps are working so I felt the intake and return lines on the heater core. The intake side is hot but the return out of the core is cold. I am thinking a clogged heater core. My question is there a control valve on the system that prevents the hot water from circulating in the heater core. If not what keeps the heater core cool when a/c is trying to cool the car. Should the heater core always be hot? I just want to make sure there is not a control valve stuck before I blowout heater core. Thanks

2003 cooper non-S

 

manual or auto climate?
on the Automatic climate control, I am 99% sure there is no on/off valve..it is full flow...the damper doors control the heat that comes into the car....
Unfortunately, many folks fail to change the coolant in these cars...should be flushed every 3-4 years.....
net result is rust, etc builds up, and plugs the heater core...which is at the lowest point n the cooling system....the fact some folks add "stop-leak" for an attampted quick fix for a leaking thermostat gasket or tank does not help...

 

It is auto climate. So it looks like it must be the heater core then. Guess I will pull it and see what it looks like.

 

In case you haven't taken care of this yet, I just had the same issue with mine. I pulled it and sure enough it had a ton of scale and crud in there. I ended up taking it to a radiator shop and they cleaned it for only 20 bucks. Car now blows hot air.