eh well if it's any help to u. my heaters don't work in my MA70 either. Well they do now sort of.
First thing i did was bypass the Valve in the engine bay at the firewall on the passenger side. That at least allowed hot coolant to flow into my heater core. But it still did not work, then i found out the heater switch (the climate control) was the other culprit, and by pushing the slider VERY hard to the right (hot side) that hot air would come out. Then as soon as i let it go, cold air would come out.
I haven't had any luck fixing the switch, so i buaght another one of manny, should be here soon. It could be a common MA70 problem, i'll rip down my bad switch and see what i can see, i reckon it's a common problem, most likely a bad solder or some kind of bad connection.