78 burb A/C question

[4 Wheelin Fudpucker]

Right now in the middle of winter, my new to me 78 burb will not go to defrost.
It is stuck blowing out the lower vents and the A/C vents, no matter how I move the lever nothing happens.
Being that its not mechanical, there is no cable like on the hot/cold lever.

I just need to get the deverter to go up to the windshield.

Is there some pot or relay I can look for thats out, or the power going to it?

This summer Im ripping out all the A/C and converting to the manual heating system from my 79. Till then Im freezing me lug nuts off