Help 77 Olds 98 no heat

My son is restoring a 1977 Olds 98, but we can't seem to figure out the heating system problem. Radiator has been replaced, thermastat is good, all vacum lines have been replaced. There is no leak in the heater core, and the whole system has been flushed. Can anyone shed some light on this before the kid freezes to death this winter?
Thanks
Trish

Are both heater hoses getting hot? If not, coolant is not getting to the heater core. I can't recall if that model year has a "hot water control valve" located in the heater hose or not. Many GM vehicles of that vintage did. It's purpose was to shut off the heater core from getting hot coolant through it when the system was placed in "MAX A/C" or full cold 60 degree mode on climate contol vehicles. This valve is vacuum controlled. If it's a problem you cold eliminate it for winter use and plug the vacuum line for now. If the heater core actually has hot coolant getting through it, it's most likely an isuue with the programer,if this car is equipped with climate control also maybe called "Tempmatic" (60-90 degree settings on the control). It's located on the right side behind/under the glove box. It must be mounted correctly to operate properly as there are check balls inside it. The programer controls the temp door movement. The temp door has a metal rod coming out of it that is held to the crank on the programer with a white plastic piece. Pop this piece out of the crank arm on the programer and see if you can manually more the temp door. If you can, you move it and get heat, you have found part of the problem. Really on this vintage of vehicle your better off converting the temp control to full manual temp control like the base 88's and 98's of the same vintage. To do this get a new temp control cable for a base C60 (A/C but not climate control) equipped vehicle and attach it to the temp control lever on the control head and the other end to the temp mode door/valve. It will be manual temp control now like many cars still are today. Please repost if you need further detail or information.

Thank you so much. We tried this this afternoon, and woohoo he has heat. Just in time too they are talking 15 degree temps here :(.

Trish

Which was it? Hot water control valve or Programer issue?