Overheating Blower Connection at Fuse Panel

[Classics Fan]

I recently posted about a problem I was having with the cigarette lighter in my 1971 Jimmy Custom with AC. Related to that post and subsequent thread I discussed how I found the HVAC blower connection at the fuse panel melted. (I had begun smelling something hot just previous to this when the blower was run on high). I chalked that up to a bad/corroded/oxidized connection and replaced the melted female spade connector and short length of wire that showed signs of melting, and added a 20A inline fuse at the panel connection.

Fast forward to yesterday, the first time I’d driven the vehicle after the work described above. Within 10 minutes or so of the blower being run on high speed I caught a faint whiff of hot electrical but it seemed to go away. However when I returned home and looked I found the new fuse panel connector had a dark spot on it and it cracked when I pulled it off the fuse spade. It only gets hot with full voltage to the blower on high, not on lower resisted voltage at lower speeds. Also, the 20A fuse did not blow. I’m confident the connection to the fuse panel was tight.

So my question to the folks who understand electrical much better than me, what can cause this? I assume high resistance in that circuit? Blower motor? Or something else?

[dagnabbitt]

I am not an expert, but if the failure point is where you describe it might be due to increased resistance: likely by poorly crimped connectors, or a poor connection with the fusebox terminal.

[D.B]

I had a melting connector issue with mine and found out it was a bad ground strap on my blower motor. I made sure it was connected to a good ground spot and it fixed my problem.

[Classics Fan]

Originally Posted by dagnabbitt

I am not an expert, but if the failure point is where you describe it might be due to increased resistance: likely by poorly crimped connectors, or a poor connection with the fusebox terminal.

I’ve double checked the crimp and connection. Both are good and tight.

[Classics Fan]

Originally Posted by D.B

I had a melting connector issue with mine and found out it was a bad ground strap on my blower motor. I made sure it was connected to a good ground spot and it fixed my problem.


Attachment 2413844

I was optimistically hopeful your suggestion would be the solution. I disconnected the blower ground on the firewall/cowl, wire brushed the attachment screw, washer and ground wire eyelet and reattached it. Unfortunately the short length of wire (approximately 2”) between the fuse panel and the inline fuse I installed still gets hot within a few minutes of the blower running on high speed. The wire getting hot is the same gauge as the orange factory wire it’s connected to that runs to the blower.

[dmjlambert]

Check to make sure nothing is dragging on the blower squirrel cage, such as an obstruction or rats nest. That will make the motor draw more current.
Make sure the connector on the fuse panel is good and clean and doesn't have rust buildup, that will cause resistance and heat. There's only 2 screws holding the fuse panel on, remove them and flip the fuse holder over and inspect the back for rusty connections and melted plastic there.
Make sure you have a 16 gauge 6 to 9 inch length of fusible link wire connecting the main 12 gauge red wire at the junction block near the battery. That is what helps protect the unfused 12 gauge wiring in the truck.

[Classics Fan]

Originally Posted by dmjlambert

Check to make sure nothing is dragging on the blower squirrel cage, such as an obstruction or rats nest. That will make the motor draw more current.
Make sure the connector on the fuse panel is good and clean and doesn't have rust buildup, that will cause resistance and heat. There's only 2 screws holding the fuse panel on, remove them and flip the fuse holder over and inspect the back for rusty connections and melted plastic there.
Make sure you have a 16 gauge 6 to 9 inch length of fusible link wire connecting the main 12 gauge red wire at the junction block near the battery. That is what helps protect the unfused 12 gauge wiring in the truck.

The blower is clean and not dragging. The connection at the fuse panel is clean and tight. There are actually two fusible links, one directly off the battery and another at the junction block. I’ll pull the fuse panel to check if there’s anything going on on the back side.

[67swb72klb]

The fan motor might be bad drawing too much power?

[HO455]

At this point if it was my truck I would check for voltage dropping across components. You can start at either the motor and work to the battery or vice-versa. The process is to use a voltmeter to test a component or wire for voltage by putting the meter leads on each end of the wire or the connections on a component while the circuit is in operation.

If you start at the motor when the motor is running put the black lead to the motor ground connection and the red to the positive power to the motor. Record the voltage.

Then put the black lead where you had the red lead and the red lead gets moved to the blower motor feed on the AC blower speed relay. Record the voltage. Since your checking for voltage on a single piece of wire you should read zero volts. If you are able to measure some voltage it means there's a poor connection that causing resistance to the circuit. This resistance causes the amperage drawn by the circuit to increase.

On components that have moving contacts (Like switches and relays) it's good to check them several times after operating the contacts. Sometimes contacts work good one time and bad the next.

Next the black lead goes to the blower feed side of the high speed relay and the red lead goes to the 12 power feed at the relay. Once again record the voltage.

Now check the wire from the relay to where it hooks to the fuse panel.

Then you can check the fuse block by putting the black lead where the blower power hooks to the fuse block and the red lead where the 12v positive power hooks at the firewall connector in the engine compartment.

Ideally you should read 12 volts with the first test at the blower motor and zero volts on the rest of the tests. Any component tested that shows more than .5 volts should be inspected to determine why it is dropping voltage.

Good luck!

[Classics Fan]

Originally Posted by HO455

At this point if it was my truck I would check for voltage dropping across components. You can start at either the motor and work to the battery or vice-versa. The process is to use a voltmeter to test a component or wire for voltage by putting the meter leads on each end of the wire or the connections on a component while the circuit is in operation.

If you start at the motor when the motor is running put the black lead to the motor ground connection and the red to the positive power to the motor. Record the voltage.

Then put the black lead where you had the red lead and the red lead gets moved to the blower motor feed on the AC blower speed relay. Record the voltage. Since your checking for voltage on a single piece of wire you should read zero volts. If you are able to measure some voltage it means there's a poor connection that causing resistance to the circuit. This resistance causes the amperage drawn by the circuit to increase.

On components that have moving contacts (Like switches and relays) it's good to check them several times after operating the contacts. Sometimes contacts work good one time and bad the next.

Next the black lead goes to the blower feed side of the high speed relay and the red lead goes to the 12 power feed at the relay. Once again record the voltage.

Now check the wire from the relay to where it hooks to the fuse panel.

Then you can check the fuse block by putting the black lead where the blower power hooks to the fuse block and the red lead where the 12v positive power hooks at the firewall connector in the engine compartment.

Ideally you should read 12 volts with the first test at the blower motor and zero volts on the rest of the tests. Any component tested that shows more than .5 volts should be inspected to determine why it is dropping voltage.

Good luck!

Great step by step instructions, HO455. They make sense. I’ll let you know what I find. Thanks!