I just got my 86 N/a the other day.
Today I noticed that the heat doesn't work. No matter how long I run it, nothing but cool air comes out.
Also, when I push the differen't buttons for defroast, or for the air to hit my feet, it just keeps coming out of the main vents above my CD player.
My A/C is disconnected but not yet removed (it came like that). I filled my coolant.

What could be the problem?
One of the heater hoses ( the one on the driver's side of the engine compartment) is hot, but the other isn't.
My dad said he had the same problem on his 1987 mazda 626gt, and he blasted the heater core out with C02 because it was clogged.

Any advice?

 

The logicon (heater control box) is bad. It is very common on these cars. Your best bet is to search the parts for sale section for a used, but working one or check out Icemark who refurbs them (www.mazdamark.com).

In the mean time you can manually move the air mix door to get heat. Look under the center dash behind the vents to see the air mix motor and door actuator.

 

I've got a Logicon, I'll send it to you for $50 + shipping!