Fan switch lever getting hot.

[70sboomerguy]

Hi Guys,

On the ac/heater control unit on my dash the chrome fan lever gets extremely hot to the touch. It goes back to normal when the fan is off.

The switch itself was kind of glitchy in the "medium" setting but it did always work on low and high.

Is there a blower motor resistor on a 73 charger, or can the switch be rebuilt?

Thanks/Dennis

[Nacho-RT74]

Yes… as far I have found, not weird… and if you remove the control unit (or if you make to look down the dash frame to the plug) will find melted the plug on back on switch. Hence why I installed 4 relays for the A/C-Heater system.

Blower sucks a lot of load, and the blower lever switch contacts are not great really.

There is a blower resistor, yes attached to the A/C box down the dash, very visible underneath the glove box on foot well area. 4 wires… dark green, light green, brown and tan.

[70sboomerguy]

Hi Nacho, thanks for the reply:)

I'm trying to understand this...So, the design causes the switch to fail overtime as the contacts are weak & excessive load?

Can you go into a bit more detail about your relay work around, maybe a diagram, if you have time.

When I get the heater/ac conrol out I expect to see it melted. I suspect that the blower resistor would still be good?

Thanks, Dennis

[Nacho-RT74]

For some reason the 73 and lates lever switch contact points design is weak, but the earliers is stronger. I haven’t known any 71/72 owner claiming about a lever switch hot enough to burn a finger, while 73 and lates is (I got burnt myself on my car switch), but from outside they look pretty much the same kind. True is 71/72 never will get a melted plug because they get a pigtail then the plug maybe after a 2” long pigtail. So IN CASE those switches also get hot, the heat doesn’t reach the plug. Heat disipates along the wiring pigtail.

Yes I have made diagrams (and pics) about what I made and can explain how and why. However is true I also upgraded my Alt and the related alt/amm wiring, since I took the relay power from amm stud. With the alt and related wiring upgrade made you can take the power from inside the cab and not running up to the alt stud.

Trust me when I say, if you want a SAFE charging system able to feed everything safely get the charging system upgraded and propperly mantenienced.

On a side note, the only speed won’t get heated the lever speed switch is the low speed, because is the default speed. You can even unplug the fan lever switch and the A/C and Vent functions will still work but just on low speed.

[Nacho-RT74]

This is the resistor block location:



And if you pull out the harness the relays for low and mid speed suddenly appears



Sorry the low quality pics, but they were taken by a Nokia 6275 cell phone (one of my favorites ever LOL) maybe 14 years ago LOL

[Nacho-RT74]

This is the diagram about labor made to the low and mid speed shown on previous reply!



On this diagram, I rerouted the original A/C wiring for low and mid speed (tan and light green) to the 86 relay prongs. These would be the trigger for the relay and are coming from control switch assembly. Then “relinked” the wiring up to the resistor block with a SAME COLOR wire to be able to hide the modification made, even rettaping the harness. I didn’t want to cut any of the stock wiring, so simply relocated the original terminals up to the relay plug, then got the propper terminals to be able to insert the new wire into the plugs (stock and relay plug)


I made the same for the heater ( yes, AC cars get a diff speed for heater, and can’t not be changed with the fan speed switch) and high speed, but located these relays around steering column area. Can’t find the diagram at this moment, but will post as soon I find it, and the explanation why used a diff location for these.

[Nacho-RT74]

Ok I found it!



Even I could install the heater speed relay along with the other 2 relays, I just decided to spread out relays in pairs (I also added relays for low and high beams on this setup build, hidded down the driver side kick panel) and since the high speed can be ONLY installed leaving the fan lever switch, the just choose to get the heater speed there. Because doesn’t run throught the lever switch. High speed power doesn’t run throught the resistor block, ALTHOUGHT the wire is spliced into the same output wire from resistor block network, but high speed won’t be affected with the power coming out from this output.

The cavity location on lever fan switch plug for the high speed is just for reference. I can’t recall the exact cavity for it, but isnthe dark green wire anyway.

[Nacho-RT74]

For this I also run a “battery” HOT wire down the dash frame from side to side, to use it as a buss power bar/juntion to feed the relays. Reference diagram about this wire. I made a mistake on this diagram showing where I took the power for the high speed, but noticed later.



Also used a small piece of fuse link as a protection for this wire network. Not really needed, but… optional.

[Nacho-RT74]

Fan lever switch can be dissasembled and cleaned… also sometimes NOS pieces can be found, but at the end the problem will float back. Aside using the relays setup, the blower efficiency will get increased. Will spin a bit faster than getting the load running throught the original switch.

Melted plug can be replaced. New ones are available from electrical suppliers or even auto parts shops on help section.

Need to say also, even you select mid or high speeds the low speed network is allways hot as soon you turn on the AC or Vent, but the load will run throught the smaller resistance available, so that’s how the high and mid speeds are routed still with the low speed hot.

[70sboomerguy]

Hello Nacho

Thanks very much for all of the information and your time. I should be able to get thru this now.

I'll post an update when I iron it out.

Thanks again, Dennis