No heat in 2002 chevy Venture

My 2002 chevy venture does not provide any heat from the cabin air system…
The engine reaches proper driving temperature normally.
Can’t heat the cabin or get any modulation of cabin temp when using A/C.
Any idea of reason for malfunction?

I had this problem on my Silverado. The heater cores on these tend to clog up with sediment. I recommend a heater core flush, that should do the trick.

When the van is warmed up and running, feel the hoses going to the heater with the heater controls in the heat position. If one is hot and the other one is not, you either have a plugged heater core ot the temp control is not working.