A/C-Heater blower overheating wiring and plugs

[Nacho-RT74]

Guys... I'm having serious problems with my blower sources and plugs all along the wiring... AND TALKING WITH ANOTHER MOPAR FAN he had a 74 Coronet since new with same stuff.

In medium and high speed I'm getting a jumping "fail". Frequently I have getting a BIG overheats at lever swicth at the ponit that melts dowm the lever plug. Some times I don't get the overheats there but because it starts on the fuse box ( blower fuse ). This overheats is able to melts any place it appears. I suppouse this heats appears also on steering column ignition harness plug what it could be very tipical.

A/C and Heater switch is different even blower is the same So I preffer ppl with A/C answer.

Have you got overheats on Lever at medium and High speed ?

Fuse overheats ? ( is the second one from bottom to top on accesories side ). Several cars here I have seen with blower/accesories fuse hole completely destroyed/melted. In fact a 73 Charger from a buddy's mine is one of them.

I don't know if blowers were made in here in Venezuela ( on those years at least 10% of the car was mandatory assemblied with national made parts even same USA cast ) and THAT could be a reason that I get overheats and YOU don't, maybe some poor quality coil or contacts inside the blower.

I got an USA rear deffog blower that works perfect and haven't noticed yet anykind of overheats at any point caused for that. Maybe isn't the same comsumption but is the only stuff I have to compare.

I would wish an answer ASAP because if you don't get that fail I think on get an USA blower no matter if used.

[71_deputy]

Nacho- most blowers use about 8-10 amps on full speed. when the med- to low is used- the power is routed thru the resister block in the blower case.

Sounds like the motor is using more amps- either by the way it is made ( 13 amp draw? ) or the motor is binding up causing more amperage draw!!!!.

check with a amp meter to see how much draw the motor is using!!!  I'm guessing the the existing wiring/ switch is only rated at about total 12- 15 amps!!!!  main wiring is only 16 to 18 gauge!!

John Mac

[Nacho-RT74]

I got same hig consumption and problems with two blowers what I think were made in here. I'll try to check amperes... but mostly testers are Alternating current... here is a problem to check amp on blower.

I would get less voltage and also amperes readings on different blower speeds, right ? Or is just a volts decay once power goes thru resistor ?

no one of you guys have melted some part of wiring with A/C blower ?

[2Gunz]

Im not really sure what you are saying.

But....

As voltage goes down amperage goes up.

So if the blower is only getting 9 volts at full speed it will draw alot more current then it would at say 14 volts.

This help any?

[defiance]

Not exactly true.  Per ohms law, amperage (and thus power consumption, since system voltage remains at 12v) is determined by total circuit resistance.  As such, when you switch to a lower setting, and an inline resistor adds resistance to the overall circuit, making the amperage & power reduce.

For example... Keep in mind I do not know the resistances of the adjuster or the motor, these are guesses, but the math, ratios, and concepts remain the same. ---

If the blower motor is 4 ohms, then at 12v it consumes 3A.  The fan is powered by 36w, the system consumes 36w.  Easy.

However, if you add a 2 ohm resistor inline through the switch, the total system resistance is 6ohms, meaming it only consumes 2A.  Also, the voltage is divided across all of the components dependent upon their relative resistance.  Since the switch is 1/3 the resistance, it handles 1/3 of the voltage (4v), and the blower handles 2/3 (8v).  Amperage remains constant throughout the system, but overall power is now 24W, 8W through the resistor (dissipated as PURE HEAT), 16W through the blower.

Anyway, since the resistor adds another component to the system, it does not decrease OVERALL power in a real ratio to the fan's power.  However, it does still decrease it

[Nacho-RT74]

ok, but to do that we need to make test on all positions... Nice, I'll do that but let'r try to return to my first question:

Some of you guys with 3rd gen and A/C gets melted/overheated plugs or areas like fuse cavity, switch lever or anywhere ?

Or maybe those guy who parts out 3rg gens have seen melted those areas on cars you have parted out ?

[defiance]

Mine had a molten fuse box. I'm not sure if it was the blower fuse because instead of trying to fix it the 'simple' way, I tore it all out, rewired everything between the alt/batt/ign switch/fusebox with higher guage wire, and put in a new modern fusebox.  Might have been overkill, but it darned sure resolved it!   I haven't actually had any melting or damage on the blower side itself, though, so I didn't replace that portion of wire.  Pretty much everything in my car from the fuse box on is stock.  However, at ANY point where there was a high-amperage connection that wasn't being replaced (blower connector is a prime example that got a lot of attention), I thoroughly wire burshed the contacts, used some DeoxyIt (got it at radio shack) to clean any corrosion, and made sure any contact had minimal resistance.  As noted above, any pure resistance dissipates its share of power entirely as heat, so if you've got 1ohm of corrosion on your contacts, that might be several watts of pure heat being generated INSIDE that plug. 

To put that into perspective, I sometimes use a 15w soldering iron

[defiance]

Actually, come to think of it - my original A/C switch was melted pretty badly, too...  Not in a way that would impede function, just made the face all warped and ugly.  It had some other damage, so I was replacing it anyway.  I'd forgotten about that.....

[Nacho-RT74]

ok we have at least one example up there...

I have cleaned and with a sand paper polished terminals before get joined all the wiring and cluster.

weird part is that I never have got melted on bulkhead or blower plugs at blower wiring, just on fuse cavity ( second from bottom to top on left side front view ) and lever switch... also one of the resistance plugs ( the single one )

[Nacho-RT74]

no one else ?

[Todd Wilson]

Old 70's Dodge trucks are famous for this.   First you need to polish the contacts on both sides of the fuse in the fuse box as they become tarnished and cause resistance and resistance causes heat.    Same thing happens in the fan switch but I do not know a fix for this other then replacing it. It will eventually burn out and one speed can work and not work.    The switch sends 12 volt down to your resister pack which controls the speed of the fan motor. On high its 12 volt direct. On the other end of things your blower motor needs a ground to chassis  which may not be good anymore due to age. Corrosion can cause poor grounds in the fan motor and the wiper motor making them not work.  Same thing also happens at bulk head connectors. Old tarnished ends create resistance and resistances creates heat. If your vehicle is all restored and painted pretty you may not be getting a good ground through the spiffy new paint and need to scrap some away for bare metal or use those star washers to dig into the paint.    Your ECU box can also look chassis ground and kill the motor.


AC and Heater dont care. The blower fan and speed is one deal. Your control switch determines if the AC compressor is kicked on or not  and directs vacuum to open and close certain vents and trap doors to direct air for defrost or floor or vent settings.


Todd

[Todd Wilson]

On my 71 Charger and my 74 Dodge truck  the resistor pack is located inside the car up ahead of the feet of the passenger. Never seen a resistor pack inside the blower motor.



Todd

[Nacho-RT74]

Yes I do know how is wired and where is located every electrical stuff on my car thanks anyway...

I'll try to polish with a dremmel the fuse terminals.

Otherwise, lever switch and plug is the other weak part, beside red terminal undercolumn ( ignition switch harness )... Maybe also try to polish better with a dremmel . I cleaned and used a sandpaper on terminals of lever plug and lever prongs but still the same.

yes recently painted, BUT blower ground is bolted with a teeth washer on engine bay and already cut the paint up to sheetmetal. Dissasembly blower and cleaned tracks and brushes. Tried with two different blowers and same results, both maybe made in here, but both are not interchangleable parts beside housing as far I remember. Internals are different ( rotors and everything )

[Todd Wilson]

Yes I do know how is wired and where is located every electrical stuff on my car thanks anyway...

I'll try to polish with a dremmel the fuse terminals.

Otherwise, lever switch and plug is the other weak part, beside red terminal undercolumn ( ignition switch harness )... Maybe also try to polish better with a dremmel . I cleaned and used a sandpaper on terminals of lever plug and lever prongs but still the same.

yes recently painted, BUT blower ground is bolted with a teeth washer on engine bay and already cut the paint up to sheetmetal. Dissasembly blower and cleaned tracks and brushes. Tried with two different blowers and same results, both maybe made in here, but both are not interchangleable parts beside housing as far I remember. Internals are different ( rotors and everything )

Where ever you got heat is where a problem is at.

As far as the switch  it may not be the plug  but the actual mechanism inside   and will burn that board and eventually go out. I know of no way to fix this except to buy a new switch. I dont know if you can successfully take the switch apart and put it back together.


polish polish polish   make those fuse contacts look like chrome!




Todd

[Nacho-RT74]

yes I can, is a piece of cake, but not sure is will be enough. I already unjoin the switch parts once and IMHO internal contacts seemed to me very small and weak to let it go all the power through.

Is there somekind of electrical grease or something like that able to get easier the current flow and get a softly switch ?. That will save from rust, dust and less worned contacts inside the switch during lever plays.