heater fan switch melt down
 

I have a 93 pick up that I had no speed number 3 on the fan switch since I bought it. I wasn't to worried about it since all the other speeds worked.

We had an ice storm and in the morning I turned the truck on and left the heater on and fan on high for 30 minutes and shut it off. The next time I got in the truck the fan was stuck on high and I couldn't move the switch at all. So I took it apart and the switch had melted. I have a switch on the way but before I install the new switch I want to make sure it wasn't something else that cause the melt down.

Did the switch just go bad or is there something else that cause the switch to melt?

If you look at the picture there are two terminals that were cooked and whole inside of one of the copper bar was totally gone. I'm guessing each bar and terminal represents a different fan speed.

Thanks

I received the replacement switch. All speeds 1-2-3-4 work. I did notice on the replacemnt ( used) that the same location showed some burning (speded 4) so I don't know if this is common. Speed 3 and 4 are still getting hot, I don't know how hot or warm these are supposed to get, I didn't let it get to hot. Speeds 1 and 2 seem to be fine.

So I'm guessing there might be a resistor problem on speeds 3 and 4 or a short somewhere. Can anyone tell me where to find the resistors at the fan? I have a testor, I'm guessing I'm looking for continuity (ground and terminal?)at the plug?

I've gone thru several of these switches before I found what contributed to the early meltdown. Since I started making it a practice to turn off the switch when turning of the truck the problem has not returned. I metered the terminals under different scenarios and found that when cranking the engine over there was and incredible spike for the duration of the starting process. There was a very minimal increase after and before starting. I'm sure there are other things that could contribute to this but not leaving it on all the time worked for me.

I went out and did a longer test on the switch. I beleive it's just the heat generated though the switch at certain speeds because of the amount of electrical current at higher speeds. I come to this conclusion because it seems that others have had this problem and I have two switches that show signs of over heating. With the switch up tight against the rest of the controls, there is no room for any type of air flow to help cool the switch. It might just be one of those thing overlooked in manufacturing.

Speeds 1 and 2 didn't get warm at all, speed 3 warmed up a little and speed 4 was the hottest but never was hot enough to melt. I got a temp of 120* to 135* at the hottest, I used a infered mini temp gauge.

I beleive that when I left the fan on high for a long period to get the ice to melt, it may have been too long and the switch. In reality I don't think anyone would never leave the heater on high for that long while driving as heating up that little cab isn't a problem.

I'm probably going to install and keep in mind only to use high speed when nessary for short period.

My 93 did this exact same thing. Still gave enough heat to get me through the winter, now it is heating up and I need the fan for the ac. Will search and find out how to take it out.