So I'm cleaning and fixing the air box assembly (under the dash). The heater core needed replacement due to an obvious leak at some time in it's life and the box had a cracked area that needed fixing.
Now I'm about to re-install the box and I remembered that the motor was only blowing in high speed. So the question is simple....is the resistor the only likely problem ?? I take it that the motor switch itself does NOT actually govern motor speed. I ask because I plugged the motor in and it only operates when the blower fan switch is in the "high" position. I did not have the resistor plugged in.

 

The answer is yes. The resistor does the low, and med, high is seperate, and will always work. Switch is good

You may also find that the wires in the plug to the resistor have melted themselves out of thier connections, so be very careful when unhookong them from the plug/ resistor.
If the plug is bad, I have a place I buy the plugs from in my old computer,local here in Md. Let me know, I'll fire the old beast up and see if I can find them

 

1973/79 F100/350 & 1978/79 Bronco:

Blower motor resistor with heater and dealer A/C (C9AZ-18591-A) is different than with factory installed integral AC and Hi/Low Comfort Vent System (D3TZ-19706-A).

Both are obsolete, available NOS

 

Best to try and get the Ford resistors Bill mentioned, they will hold up longer

 

Having the same problem with my 84 F150.Would a resistor from a salvage yard be serviceable?Or should I look for a NOS unit?
Good luck.Have fun.Be safe.
Leo

 

More than likely, it will be in the same condition as yours
If the price is right, they aren't too hard to change, so you could try one

 

Hi DustyBumpers.Thanks for the reply.
Good luck.Have fun.Be safe.
Leo

 

Leo, I didn't notice yours is an 84.
Those are still available from Ford. A/c Ford boxes run from 84-97

 

Hi DB.Yep,not the fanciest in the world(looks like a refugee from an artillery range),but it gets me there and back.Found a resistor at AZ for 24.00 plus tax.However,I will check out the Ford branded one at the local
Ford store tomorrow.Thanks for the reply.
Good luck.Have fun.Be safe.
Leo

 

They don't have to be fancy, just dependable!
My favorite oldest one here is my 89 F 350
I use it as much as the 15 F 450
I just like that old truck. Bought both new, and they both are still new ( to me)