A/C circuit overheating and blowing the fuse.

[73runner]

Having a problem with the a/c fan circuit overheating... It's been a problem for a while in that it keeps cooking off the fuse. The fan switch connection and wires are cool as are the fan resistor wires and connectors.. The fuse connection toward the outer edge of the fuse box has cooked the fuse box and is now almost free. The main buss bar for the fuse box is ok but the fuse clip is a little rusted. The outer one is pretty cooked and rusted and blued with heat. I've cleaned the clips before and it seems to extend the fuse life.

My question is, has no one else run into this problem. I don't really want to put in a separate in line fuse for the fan. I have a replacement fuse box and harness but want to figure out the problem first.

Any ideas or previous experience would be great.

thanks

 

[Nacho-RT74]

how is the lever fan switch ? that's the point where mine overheated untill melt twice the insulator on back of switch. I could feel the heat up to the lever.

Ended upgraded everything with 4 relays, one for each speed ( low, mid, high and heater speed wich is a diff one from the AC system )

The AC blower suck LOT of load from electric circuit ( I think the most allong with hazzard lights )

 

[Nacho-RT74]

however... fuse never blowns, I just get overheats I gueess due poor contact to the required load

 

[73runner]

how is the lever fan switch ? that's the point where mine overheated untill melt twice the insulator on back of switch. I could feel the heat up to the lever.

Ended upgraded everything with 4 relays, one for each speed ( low, mid, high and heater speed wich is a diff one from the AC system )

The AC blower suck LOT of load from electric circuit ( I think the most allong with hazzard lights )

Switch and wires to fan switch are cool to the touch.

As for the relays, I like the idea. Where in line did you place them?

thanks

 

[Nacho-RT74]

I spreaded out all around the dash frame... sorry no pics because I'm in Spain and my car is in Venezuela ( my PC too LOL ), but I think can grab a diagram I posted somewhere

- - - Updated - - -

found it!... This is a relay upgrade I made on my car, with hidden relays inside the cab to make them not visible.

there are 6... 2 for headlights and the rest for AC-Heater system as explained.

Which I did is take the power for relays from ammeter stud ( alt side ) to feed relays ( with a fuse link wire to extra protection ), didn't cut wires, just removed from original plastic insulators and placed into the relay plug, to trigg it out, then reinserted a wire of same color between relay and original plug ( and tape it back to the harness ), to get the source out to the blower ( or light ). So in a wiring overview under the dash, you won't be able to see the relays but will look like allmost like an untouched harness

Of course I did this AFTER make an upgrade on my charging system and wiring... otherwise will burn the bulkhead alternator terminal. And relays are really close to the original plugs

dark green is max speed blower, brown is heater... Relays are located around brake pedal/steering column brackets

Light green and tan are low and mid speeds... relays are located between AC box and glovebox liner.

lighst are hidden by the kick panel

I spread them in pairs, to not get a BULK of relays in just one place ( since actually there is not room anywhere ) and makes it easier to feed them from positive, just splicing the positive in pairs.

 

[747mopar]

Have you checked the blower motor? a bad bearing will wreak havoc. Check for damaged wires and check every connection, how is the motor grounded? (could be a grounding issue). If you have an amp clamp throw it on the motor lead while running.

 

[73runner]

Nacho... Mil gracias por tus ideas y diagrama. Muy bien explicado..... A thousand thanks for the ideas and diagrams. Very well explained.

747mopar.... Thanks for all the ideas too. Sometimes it's the simple things... I checked the blower motor ground ( it was good and clean) but will now check it again with an amp meter and tester that can also show resistance through the motor. Any idea what it should read? If circuit is protected with a 20amp fuse I shouldn't think it should pull to much more than 10 to 12 amps... But I'm just guessing here. While I'm at it, I'll throw it on the line coming into and out of the fuse box to see if I'm getting a major drop across the fuse which I'm pretty sure I am.....


As for the blower motor bearing.....Motor is new and blows very quietly even on high and the air coming out of the vents is stronger now than I ever remember.


After nacho's comment I figured that as long as I'm fixing stuff, may as well look into upgrading the lights a bit and relieve the 40 year old switch from having to handle all that load directly. I was reading the light upgrade thread and it states that the wiring in our cars were never much more than just marginally adequate. So I'm thinking that the fuse and pad from the fan slowly cooked the circuit and raised the resistance in the connector until it cooked off the fuses..... So I'm going to check the load across the circuit first and as is and then after splicing in a new line from the fuse until the wire is good and check it then.


Going on a little trip to the Keys with the family so it'll have to wait till I get back....but will post some pictures when I do.... So you can see what I'm talking about....


Thanks again guys!

 

[747mopar]

Something to think about, Summit sells Zoop headlights that bolt right into the factory buckets and except Halogen bulbs. If you go this route use a relay.