On my '69 Cutlass (non-air car), the heater blower only works on the highest setting. Is there a relay for the lower settings, or do I need to check for something else?

 

Classic resistor failure.

 

X2. The resistor is by far the most likely cause. Non-A/C blower motors are powered directly from the switch on the dash - there is no relay. Start by pulling the connector off the resistor in the HVAC box on the firewall. Look for signs of overheating or burned contacts. Remove the resistor from the box and look at the crimped connections and resistor wires for corrosion or breaks. If this all looks good, with the key in RUN check for voltage at each of the terminals at the resistor connector with the switch moved through the positions.