The heater works fine, but the dial that has the 4 fan settings is messed up, it only works on setting 3; 1, 2, and 4 don't work, what could this be?

 

Typically that's a blower motor resister, located on your "heatbox" on the passenger side firewall, to the right of the blower motor it's self, it has a big wide 4 or 5 blade/pin connecter.

Well that's where it is on my '84 with AC.

 

If high is the only setting that doesn't work, the resistor is fine and the problem is with the high blower relay or it's circuits. What year and model do you have? Does it have auto climate control or manual HVAC?

 

I have a 2001 Chevy Blazer LS. It is manual, if you mean, (do you turn it on yourself?) Everything was working fine, I drove it one morning all the heat settings worked, then that afternoon, the only thing that worked was setting 3.

 

1, 2, & 3 are controlled by the blower motor resistor. 4 is full +12V through a relay. From the sounds of it, both the resistor and the relay are at fault. The relay is easy to test with a 12v battery, a multimeter, and some test leads.

I think I posted the test procedure for the resistor pack a long time ago, but here are the resistance values for given terminal combinations again: A-C = .26 ohm, A-D = 2.1 ohm, and B-D = .71 ohm. The connector and schematic of the circuit inside the resistor is attached.

 

Good catch Kyle! I misunderstood the symptoms. I agree, there has to be two problems.