Hyundai Matrix heater problem

Hi,

It's a 2001, came in with suspected air con problem (not cooling). But ac
system is working, expansion valve block at back of engine bay is chilled.
Ambient is about 15 degrees c, temp from vents with heater set fully cold is
about 20. So, it looks like the heater is stuck on a bit. I found the heater
control servo on the left of the air box, removed this and manually pushed
the controls to fully cold - still it heats +5c with the ac cold.


Any ideas?

Thanks