70 chevelle non a/c car , htr fan only works on high , what could be the problem. thanks

My 72 has the same thing. I'm Going to look out by the heater motor and under the dash on the heater box. There may be some sort of relay to run the slower speeds. I just helped my son change one on a newer grand prix, so i'm hoping they are along the same line. Not sure though.

I think the non a/c car had three speeds? There should be a relay on the firewall in the engine compartment located near the top right side. I replaced the one in my '70 that is an a/c car and it works great now. I was told the relays are the same, anyway it's probably the relay or the fan switch.

I think when you run tjhe blower on hi, you bypass the fan resistors mounted in the blower housing and get full power to the fan.

So, it could be the switch (since no low or mid) or the resistor wires. Mine would work on low/mid if I wiggled it. The orange wire running along the firewall to the blower motor was also bad.

Check your blower motor resistor. The blower fan builds up resistance and will eventually wipe out the resistor from too much amperage drawn across it. Fan is probably bad as well as resistor pack. You have high speed because it is the only speed that doesn't go through a resistor. It uses full voltage to spin the fan. Also on non a/c chevelles there is no blower motor relay! The amperage is so low it doesn't need one. Hope this helps:)

I had the same thing after I redid some of my stuff. Turned out to be the resistor, inside the car on the top of the heater housing. It has three wires and it goes into the top of the case....about behind the glove box on the 70 anyway.

Sounds like a classic problem with the resistor.