Heater took a crap

[littlee_domn8r]

Hi all. Haven't been on here in a while but see alot of new people. I have an issue with my trucks heater. I went to turn the fan on the other day & sparks flew from under the dash. Needless to say, now it doesn't work. Am I going to have to replace my entire control unit? Anyone ever had this happen? Thanks in advance for any help you can give me.

[LILRED66]

If it was under the dash, it is probably the heating element on the backside of the heater box under the dash. It is attached to the backside of the box with two 1/4" screws and has a wiring harness plugged into it. I would check this item first, because it sounds like that may be your problem.

[jwart]

i've got thrift heater - single knob control, could it be the resistor for the fan speed control. believe lilred is talkling about that part.
ClassicParts.com has part#68-375 for about $7. none of my local auto parts could even find listing for it anymore. Napa did have a blower motor for $20 on hand. i ended up temporarily running my fan on hi with toggle switch for awhile. does your heater normally heat ur cab enough for ur climate? 1st winter using mine as daily winter driver & been putting off replacing heater core-probably my weakspot getting enough heat.
merry xmas & stay warm jw

[rickf]

Yeah... when LILRED wrote "heater element", I was thinking what? The "heater element" for these is the thing we call the heater core, heated by engine cooling water, in turn heating the air (but you know all that, I'm boring you).

On the other hand, what is a resistor but a little bit of wire that dissipates some voltage by turning it to heat?

So, everybody is right.

I agree the most likely thing is the fan speed resistor pack. WHen one of the coils goes it can sproing over and make a short, there's your sparks.

Anyone know what the values are for these resistors? If mine ever goes I was thinking of putting in some potentiometers (aka variable resistors) so I could "tune" my fan speeds.

I put in a fan motor on the spendy end awhile back (about $45, mainly hoping it had better bearings and so would outlast the $16 motor). I was surprised how strong it was compared to the old stocker. On high it is high, of course, but it draws more current than the original so on low and medium it hardly goes. So I need some slightly "smaller" resistors, or adjustable ones. But I don't know where to start, what range to look for.

[littlee_domn8r]

The sparks came from up where the controls are. I went out & messed with it this weekend. Put a new fuse in & it works. I couldn't see any visible burn marks, but I did notice that the 3rd lever (out of 4) seems to be broken & it wasn't before. It just flops around.

[Captainfab]

It sounds to me like maybe your fan switch shorted out thru the lever somehow. You might want to pull the heater controls out and have a look. You should be able to get it out a little ways without disconnecting the cables

[LILRED66]

Yeah... when LILRED wrote "heater element", I was thinking what? The "heater element" for these is the thing we call the heater core, heated by engine cooling water, in turn heating the air (but you know all that, I'm boring you).


I am not talking about the heater core...I am talking about the heater element attached to the backside of the underdash plenum box. It is an electrical item with a coiled resistor in it that heats up to red hot when current is applied. It is not the heater coil that is in the underhood heater box.

[littlee_domn8r]

I must be missing some parts. the heater element is just sitting there inside the box in an open hole in the box.

My heater has always kept the cab plenty warm. I don't drive it much in the winter anymore, but used to a few years back. I have the deluxe heater.

Thanks for all your help!

[joe231]

heater element
it is called a blower motor speed resistor. it is placed inside the heater box for cooling to extend the life of the resistors. depending on which wire is energized, via the blower motor switch, the speed of the fan changes, with no (or very little) resistance on high.
here is a pic and link

Blower resistor

rickf, you have a multi-meter? you could measure your stock resistor
if not, I will try to get you values in the next day or 2.