Heat not working

1990 Grand Am 4 cyl.
Blower works, changed thermostat.
Heat does not work. Checked Chiltons & Haynes, no help.
Is there a heater valve/solenoid? Thanks in advance.

your hot to cold selector is cable operated. the cable may be broke or disconnected. trace the cable from the heater control to the door actuator rod and see if it's moving.

How long have you had car? If its a new to you car check to see if last owner bypassed the heater coil.