AC relay melted... ever see that??

[aggiedave98]

The AC/heater blower on my '89 suburban wasn'ty working on any speed except high. I tested the switch, resistor pack, etc. and finally found that the problem was the wire that goes from the resistor pack to the relay had melted the connector at the relay. That had caused a loose connection.

Any idea what would have caused enough current to melt it??? I cleaned it and connected it up again and it seems to work fine. Is it dumb to think it may be ok now??

Another piece of data is that the common wire on the switch itself blackened the switch connector as well.

[87 STEPPER]

I know you said you ck the resistor pack but remove it and see if any of them are contacting each other. If so gently bend them so they dont hit.

If that looks good then i think i would replace the relay. The relay motor/winding could be having whats called dielectric brake down and that could of caused the connector to melt and the wire to discolor.

One other thing you can do is remove the blower motor and see how easy it spins to see if the bearings are ok.

[aggiedave98]

Just to follow up so this is in the history and Slonaker is asking...

I didn't ever find out for sure what the problem was. I had replaced the resistor pack a few weeks before this (because I thought it was my problem and you can't return electrical parts), but my guess is that the relay went bad and the extra resistance caused the extra current draw and the melting.

The other thing I did was replace the blower switch in the cab for $5.99 (low/med/med-high/high switch) because those contacts looked corroded a little. That could also cause a higher current draw, but I think the melting would have been at a different spot.

So again, I think '87 Stepper is right with the relay itself.

[Slonaker]

Originally Posted by aggiedave98

Just to follow up so this is in the history and Slonaker is asking...

I didn't ever find out for sure what the problem was. I had replaced the resistor pack a few weeks before this (because I thought it was my problem and you can't return electrical parts), but my guess is that the relay went bad and the extra resistance caused the extra current draw and the melting.

The other thing I did was replace the blower switch in the cab for $5.99 (low/med/med-high/high switch) because those contacts looked corroded a little. That could also cause a higher current draw, but I think the melting would have been at a different spot.

So again, I think '87 Stepper is right with the relay itself.

Wow. You should be, like, an electrical engineer or sumthin'. Oh, wait, you are!

I need to replace the relay, then. I have a new dash control with the fan switch in it that I have not installed yet. I also need to replace the melted connector and everything. I want to try the fan upgrade mentioned in the other post today, but I should probably get everything working right before I start working the system even harder.

Thanks for the update.

Slonaker

[dwcsr]

What you’re talking about is called thermal overload. The short version is when a connection has a resistance between connectors and that extra resistance creates heat that eventually burns up the connecter on the relay/switch/ what ever it’s connected to or the wire side connector. Thermal overload usually does not pop the fuse. It can melt the solder in a fuse that holds the ends on and still no pop it.

The cause is the zinc coating on connectors get corroded like you thought creating the resistance, the item it self is usually ok, just the connector part is burnt up as in your case. It happens a lot on older heater, A/C parts and headlight switches anything that has a fairly heavy load. Moisture and humidity like we have here also play a role in making the corrosion. Its one of the reasons they still use Fusible links that have soldered ends and bolted to a battery tap for main power circuits. Fusible links will melt under a thermal overload if properly sized.

[dwcsr]

I actually got the reason from a booklet that www.Madelectrical.com sells. I had for many years seen the remnants of the effect and what happened and where but never new the actual term for it and the cause till I read the booklet he put out.

[Slonaker]

Originally Posted by dwcsr

I actually got the reason from a booklet that www.Madelectrical.com sells. I had for many years seen the remnants of the effect and what happened and where but never new the actual term for it and the cause till I read the booklet he put out.

You are way ahead of me. I don't know squat about electrical stuff. My Dad was a whiz with anything electrical or electronic. I depended on him when I should have been trying to learn.

Slonaker

[aggiedave98]

funny thing is I am an electrical engineer...

I work in the semiconductor industry though (we make chips for cell phones, digital cameras, cable modems, mp3 players, etc.)...

[Slonaker]

Originally Posted by aggiedave98

funny thing is I am an electrical engineer...

That was why I said it! There has to be another Aggie joke in this somewhere.

Slonaker

[dwcsr]

I see electricity as being almost the same as hydraulics and pneumatics just the switches, regulators and conduits are different. The pressure, power and resistance is different and measured differently. But the base principals are the same, you create and put power into a curcuit to get work out. This is a very simplfied analogy but if you see the relationships it makes it easier to fix all of them. I did aspire to be a builder of robots as a child so maybe that makes it easier for me to see it that way.

[aggiedave98]

Originally Posted by dwcsr

I see electricity as being almost the same as hydraulics and pneumatics just the switches, regulators and conduits are different. The pressure, power and resistance is different and measured differently. But the base principals are the same, you create and put power into a curcuit to get work out. This is a very simplfied analogy but if you see the relationships it makes it easier to fix all of them. I did aspire to be a builder of robots as a child so maybe that makes it easier for me to see it that way.

Very much so!! Especially semiconductors... a transistor is a 3 "wire" device which is like an inline vavle with 1 terminal being the input, 1 being the output, and one being the on/off switch.

Also what's interesting is the difference between digital and analog. Most of the chips we do are ditital w/ transistors being either on or off, but then analog circuits are much more similar to what I'd call analog circuits in a car like a carburator. The digital circuits are fuel injectors. On or off, that's it. But the carb is analog where there's 4 circuits all working by sending various amounts of fuel under different conditions. I find things like carburators much more innovative than fuel injection. The same thing w/ an auto tranny... VERY interesting... the vavle body is an analog circuit....