Climate control economy mode woes

[carson]

In my 83 300TD, when I push the economy button on the climate control after turning on the car, the blower fan won't start spinning unless I press the normal or defrost modes first. Once the fan is spun up, I can switch it over to economy mode and everything works as expected. I have an extra climate control button module laying around and the same thing happens when I swapped that in, so it makes me thing there must be something like a weak relay causing fault. Has anyone else run into this issue or have some suggestions as to what could be the cause? The blower motor is a fairly new URO replacement and seems to work fine.