Partial troubleshooting: Fan control switch and blower motor not working

[Coelacanth]

Going through all my wiring and electrical this summer, when I reinstalled my heater control panel, I discovered my blower motor didn't work on any setting. Low and high were totally dead; medium made a slight click of life but nothing else. I restored my heater box several years ago but the car hadn't started long before that, so I wasn't looking forward to disconnecting all the linkage, hoses, nuts & bolts to remove the heater box and replace the blower motor. Well, if you have a 1968 - 1970 B-Body (this is for a 1970 Charger), here's another thing you can do to troubleshoot a non-working blower motor.

I had some advice from member Daytonavic that the fan control switch could be the culprit. You can carefully pry up the 3 metal tabs holding the circuit board in place, and inspect the metal contacts inside. Yours will probably look as bad (or worse) than mine, with black carboned-up scoring and traces:

After some cleanup with Sprayway cleaner and a little polishing with 1000-grit sandpaper, things looked much better; I also touched up the raised lettering with some fresh white Sharpie oil-based marker. Recall my spare control plate looked like the one on the left:

The switch plate now looks as nice as my good one, that I already installed in my car:

I still have to tweak something inside, but whereas before, I had almost no life whatsoever from the blower motor, now it's working again on low and medium. High fan speed still doesn't work but I know it's the switch, not the blower motor, and this resto process was a lot easier than doing an R & R of the heater box only to have no improvement. I may just need to bend the arm to make a better contact with a low contact point for the light green "high speed" wire.

 

[MWbirdLOVER70]

is the blower box resistor good. I’ve had low and medium but no high. Replaced and viola

 

[Coelacanth]

is the blower box resistor good. I’ve had low and medium but no high. Replaced and viola

Yep, I already installed a different fan switch and it works on all speeds. This heater control assembly is a spare I'm restoring. Everything else was good. I just wanted to point out a relatively easy part to test and fix before yarding out the heater box.

 

[Bird 426]

Same issue with my Road Runner, low and medium work fine, if I wiggle the switch on high it will work, till you hit a bump. Got another used switch, same identical problem. This is after cleaning like you did.

 

[MWbirdLOVER70]

Yep, I already installed a different fan switch and it works on all speeds. This heater control assembly is a spare I'm restoring. Everything else was good. I just wanted to point out a relatively easy part to test and fix before yarding out the heater box.

Thanks for the info brother

 

[Coelacanth]

Same issue with my Road Runner, low and medium work fine, if I wiggle the switch on high it will work, till you hit a bump. Got another used switch, same identical problem. This is after cleaning like you did.

One of my switches works on all speeds, the other doesn't work on High. So that tells me the blower motor and resistor are not likely the issue. Maybe in your situation, replacing the resistor on the heater box might work, as MWbirdLOVER70 suggested?

 

[archangel]

Coelacanth, I just cleaned my blower motor switch as well. Curious, what continuity readings do you have on your known good switch? (continuity = 0 ohms)
Mine:
Off: no continuity between black wire (power) and any of the 3 other wires
Low: Black and Brown
Med: Black and Dark Green
High: Black, Dark Green and Light Green

The last one is throwing me off a bit. I was expecting that only the black and light green would have continuity on the High setting but looking at the internal workings the little sliding "pad", that makes and breaks the connections internally, appears to connect the 3 wires on High setting. Unfortunately the FSM does not provide detail on the switch internal connections as they relate to the low/med/high positions.

Note that I was initially getting continuity only between the dark green and light green wires on the High setting which did not seem correct. I flipped the sliding "pad" 180 and instantly got continuity between all 3 wires. Odd in that the pad seems to be symmetrical and is clean, not overly worn. I suspect that maybe the small spring underneath it has weakened over the years and does not apply even pressure across the back of the pad.

 

[Bird 426]

I thought that high speed did not go through the resister, straight 12 volts?

 

[archangel]

I agree that the light green wire (aka High) bypasses the resistors. That is why I am somewhat baffled that my switch shows continuity between the light green, dark green and black (power) when switched to High. In that configuration is it sort of irrelevant that dark green (Med) is still connected since as you stated the light green wire provides 12V DC directly to the blower motor. My switch might be faulty or maybe that is just by design.

Note that for those who might reference the Charger/Coronet FSM schematics, of the 3 different car types shown the heater switch/resistor area on the "Charger" schematic has the brown and dark green wire color labels reversed at the switch end. The other 2 schematics, "Charger w/concealed headlights" and "Coronet", are correct albeit they look different between the 2. The screen capture below is from the Coronet schematic.

 

[Bird 426]

I did not dig too deep into it, other than I bought another panel with a switch in it. I opened up the switch and cleaned it just like my original one, it functioned the same way. Had to play with it to get high operational. I live in the sort of upper Midwest region, if only med/low work, I will be fine for how much the car will be driven in the spring and fall.
Good luck and thanks for the info!

 

[devinism]

The heater switches get corrosion inside the black covering on the switch back.