Euro 107 manual climate control, I get random heat/no heat

[Bondavi]

On my Euro with manual climate control, when the temperature dials are in the COLD position, I get heat all the time from the right defrost vent. Sometimes I will get heat from the left dash vent, somtimes it will go back to cold. This is without touching the temp dials.

Because this is manual climate, how should I be looking at this in terms of vacuum, auxiliary coolant valve, pods, and whatnot? Most advice regarding climate appies to the automatic system, which I do not have.

Thanks in advance!