1978 Heater w/o Air Blower Problem

[44Sixgun]

So, I bought my 1978 C-20 Scottsdale Camper Special about a year ago.  Generally, in nice shape.  But, on the heater blower I have only had, off (switch down) and High (when the switch is all the way up).

So, I went through the "diagnosis" in the service manual and decided that the resistor was bad.  Purchased new resistor and new switch.  Also, another problem is that the wiring connector at the resistor is gone, just flat blade connectors on each, light Blue, Brown & orange wires.  Now, I have replaced the resistor, switch (I do not think either of these were bad) and the brown wire from the switch - the continuity was bad.  But, I now have a low speed with ignition on, and switch down, the same speed with the switch in the middle, and a higher speed with the switch up. 

So, what is up?  Is it suppose to always be on, two speeds, three switch positions?  Wires on the wrong poles of the resistor?  Something else.  Help. 

Pics of firewall area attached.

Thanks
Bill

[bake74]

      There is suppose to be low, medium, high.  I do not know if you went through our tech section for the wiring diagram, but that is what I am referencing.  You said you have a manual, there are manuals for our trucks in the tech section also, but I am going to stick to the wiring diagrams.
     You can find the complete 73-87 wiring diagrams here.
     On page 77-80_SBC_eng.jpg upper top right corner you will see the blower motor and resistor.  The wires you are referring to are 2 orange wires, 1 brown wire, and 1 light blue wire.
     If you were to follow the wires to your switch, you will first go to page 77-80_instrument_pg1.jpg, these 3 wires at the top left of the page flow through this page completely to page 77-80_instrument_pg2_jpg.  Which are counting from top left of page downwards would be wires #4, #5, & #6 (the 3 wires directly above the dotted line).
    Now following these 3 wires you will end up at your switch block.  The 3 wires are for each speed.  2 BRN 50B goes to block #50.  (which is also connected to 2 BRN 50A which goes to another 50 block which if you follow each wire, goes to fuse panel & circuit board on your dash cluster).  Your 2 BRN 50 B wire is for the LOW speed of the switch.
     2 ORN 52 A wire goes to block 52 which is your HIGH speed for your heater.
     And lastly your 2 LT BLU 72 wire goes to block 72 and is for the MEDIUM speed of your heater.
     Please check to make sure these wires are hooked up correctly on both ends, have no shorts (continuity on the wires, or shorted out somewhere inline) and report back, so we can further help you if needed.
     I do believe your heater is suppose to be on all the time, unless on your switch you have a off position, which I did not see on the wiring diagram, which is the way my 74 & 77 are, heater on all the time unless I unplug them.
     Good luck.

[44Sixgun]

Thanks for the help.  It helped a lot to understand how it is suppose to work, hard to do "trial and error" when you do not know what the end goal is.  Also, even with the wiring diagram, which I had, I was not quite sure which pin on the resistor was 50 and which was 52 as the "factory" three wire connector is gone and the wiring diagram is a little strangely drawn - at least to me.  But, your info helped me sort it out.   

So, I have a low speed that is on when the ignition is on (strange that there is no "off") - I have a medium, and a high blower. 

Again thanks
Bill

[rich weyand]

The blower being on low all the time is a federal safety requirement for trucks.  Concern that exhaust will be sucked into the cab and overcome the driver.  There is a federal standard for maintaining a positive pressure in the cab (when the windows are closed) so that exhaust will not come in, and keeping the blower on low is the way they do that.

[44Sixgun]

Thanks for the info on the fan always on - learn something new every day!

Now on to the Radio replacement, wiper motor replacement (as I only have one speed there, also), ...!  When does the fun end!  (:<))))))

Bill

[bake74]

Thanks for the info on the fan always on - learn something new every day!

Now on to the Radio replacement, wiper motor replacement (as I only have one speed there, also), ...!  When does the fun end!  (:<))))))

Bill

     Never what would be the point, then you would have to go and get another one.  LOL