Heat problem

No heat in my 1998 mercury sable. A/C works great. My mechanic does not think the heater core is the problem but cannot figure it out.Is there sensors or other controls I could look for?

The heating system has a blend door that allows either cool outside air into the vehicle or heated air into the vehicle. Check to see if this blend door is functioning properly.


Probably the blend door motor #XF1Z-19E616-CA - $68.36. but there are also three vacuum motors as well plus the switch. Here at my Ford dealer we see more of the electric blend door motors than the others.

OK, blend door motor and door are functioning properly. What about the three vacuum motors and the switch. Where do I look for them?