300TD Heat Question

Hello to everyone on the board this is my first post and my first Mercedes. Here is a little history on my question:<br> <br> I had no heat but the blower works fine. The A/C doesn't work either but that could be a multitude of problems. I have a 1980 300TD non turbo with about 150,000 miles. I narrowed the problem down to mostly the heater control valve in the front right side of the engine compartment. 'Not working? Take it apart' <br> <br> The large gear that actually turns the plunger was missing a tooth and in turn fried the electric motor. I went to my friendly local AC mechanic and he was gracious to give me an old contorl unit! Switched out the appropriate parts and viola!! NOW I ONLY GET HEAT NO MATTER WHAT THE SETTING! <br> <br> I reset the unit by replacing the control arm and playing around with the potentiometer? This caused all of the blowers to stop working. After a couple more tries I got the blowers to come back on AND respond to the reastat(i.e. foot blower on 85 degrees and top blower for 65 degrees.) but to no avail, HEAT ONLY. <br> <br> I know that there are issues with the A/C but can I set that reastate to just blow fresh air on cold and heat on heat? What other factors could be involved? Anyone else have this problem?<br> <br> Thank you all for your time, I appologise about the lenght of the question. Any help would be greatly appreciated.<br> <br> Todd