I am working on my 1970 olds cutlass convertible. I am in mid restoration and have replaced both the fan motor and relay, and once replaced, the fan motor will only run on high? I ordered a new blower motor resistor but it is not the direct replacement. Pretty capable mechanic and my Father In Law is a 40+ year diesel machanic and we are pretty stumped. Any suggestions on what I might try next?

Thank you in advance.

Terry

 

There are a couple of heater resisters on ebay right now...A/C or non?

 

a/c Sorry, should have mentioned that right away

 

The motor is obviously O.K. There are only several items which can cause the situation. Assuming that the new relay is working correctly (you should be able to hear it "click" when switching between "hi" and slower speeds), and everything is connected correctly, here are some things to check:
The 30 amp in-line fuse (if it's blown look for a short)
The "ground" on the relay
The switch on the dash
The dropping resistors
An "open" connection in any wire or connector

If you're good at tracing circuits, there's a schematic on page 1-18 of the 1970 Olds chassis service manual.

Once all components and connections are verified as "good", it should function correctly.

 

Do you have a chassis service manual? If not join wildaboutcars.com it's free
pg 1-18 or fig 1-40 flow chart should walk you through it.
http://wildaboutcarsonline.com/cgi-b...aldisplayed=50

Pat

 

As implied above, your next move is to examine the wiring diagram, which will be located in the Air Conditioning section of the Chassis Service Manual, and see where the electrons are supposed to go.

If you have high speed when you put the switch on High, then you have good power from the heater fuse through the speed switch to the relay, and from the battery through the heavy wire and High speed fuse, through the relay and to the motor.

That leaves the relay, the switch, the lower-speed switch wires, and the resistor block as possible culprits.

Check relay for power out to the resistor block when on speeds other than High.
Check wires from switch to resistor block for power at the selected speeds.
Check for power out of resistor block when switch is set to speeds other than High.

- Eric

 

Check the resistor connector to make sure it does not look like mine did - all burned, pitted, and melted.
If so Rockauto sells a new one for a few bucks.


Heck, check all the other connectors and replace the individual terminals or the whole thing if needed.