Temperature know on dash after replaced heater core

1997 Buick Skylark V6 3.1Ltr

so a couple years ago the heater core went and it was bypassed at the firewall.

over the weekend i had it fixed and i bought the heater core.

now their is no heat plus temperature knob on the dash has some resistance and will rotate back a bit when turned and let go.

i took it back this morning before work and the guy says it may be the heater valve, but i do not think there is a heater valve in my car.

i say the air panels/diverters are not lined up right.

the heater core seems easy to install(well, once you take the dash apart).

it is only a mini radiator with two small pipes extending. it does not look like it is necessary to mess with any cables or flap/diverter doors.

any ideas/suggestions?

i just want to get some feedback because i am supposed to go back in saturday morning - maybe i shouldn’t. this guy is not going to want to go back under that dash. i may be better off finding someone else to fixe it.

thanks for any insight