CCKen

Yeah, but she ain't no 17 year old apprentice Nun. Wires can still chafe over the years. Several folks have found broken wires in the HVAC system.

Checking continuity with an Ohmmeter is a good idea.

goatherder

So...I plugged in the new resistor bank and guess what? Now I got a hot on the blower connector. Cool. So I plug it into the blower (making sure it's firmly connected) and guess what? Blower starts up! Runs on all different speeds and appears to be doing just what it is supposed to do. Woo Hoo, I'm stoked. Showed my wife "See Baby, fan's got all it's gears, just like it oughta".

She was impressed, until I started twisting the selector switch; checking the different modes. And then it was "what's that smell?" And then the fan stopped...and now only has high gear. She was less impressed after that...and so was I. I'd just smoked a $20 fan resistor.

I have another HVAC control in the mail from Ebay. I'll install that and another $20 fan resistor and see what happens....

Seems I may have some kinda failure in my selector switch. OR - downstream from that switch on one of those circuits. I'll stare at the schematic some more and drink some wine...and maybe it'll come to me.

CCKen

Your blower motor may be drawing too many Amps and melted the thermal fuse inside the resistor block. The wiring schmatic doesn't show this fuse but it's there.

goatherder

Well, that may be the problem. This new resistor pack lost the same component as it's predecessor - I could smell it before it quit, and it's the one that spans the back of the resistor pack, isn't coil-shaped; just tubular. It cooked off and now its open...so that must be the thermal fuse. I guess I'll have to figure out a way to test the damn blower motor. Not easy to connect jumpers as it kinda down in the abyss.

SO in that schematic on the AC/Heater control box...there appear to be two heat selector switches. So I guess it's a double switch or something? I'm guessing that one side controls the blower and the other controls the AC compressor? (so in pos 7&8 the compressor is disabled)?

Also, WTF are those round symbols with the X inside over on the right, anyway?

CCKen

.

goatherder

The fuse melts at around 128*C (262*F). If the passageway for the blower air is blocked before it gets to the Resistor Block (in the air passageway) it may cause an overtemp and melt the fuse.

Resistor Block appears to live in the plenum behind the blower. Since the mode selector seems to send air to the correct vents, I doubt the air passage is blocked. Seems all the air no matter where it's going would have to pass that resistor block along the way...

Do most all these blower fan resistor blocks have a thermal fuse? I wonder what would happen if a bridge were soldered across that thermal fuse so as to bypass it.

CCKen

I wouldn't do that! Fuses blow for a reason. If you do that there's a chance you could melt the resistor connector, or worse.

~~~~

For the short period of time you did have the blower working, did it seem to be delivering a large volume of air out of the vents?

If you don't change the blower right away and want to check it out somemore, you may want to select MAX AC (recirc air) on the Mode Selector (to bring in cabin air vs. outside air) and see if the fuse blows again. If it doesn't there could be blockage upstram of the blower. If it still blows, there could be blockage downstream of the blower, or the blower motor is defective.

Some pics for your viewing pleasure:





Critter nest material in the ductwork.

goatherder

Well...I probably wouldn't either. Just playing devils advocate on that one...


Yeah it seemed like mode switching was working, but then yesterday I was trying to switch modes (blower still works on hi speed) and it did not seem like it wanted to switch.

When I initially got it working, vehicle was not running. I switched between blower speeds a bunch of times, then tried the mode switch. Nothing. Duh...no engine vacuum. So I started the Jeep, tried the mode switch. It initially worked good, but after maybe 15 seconds I started to smell the fuse, and then a few seconds after that...poof. Now only hi speed blower works, which as I understand it bypasses the resistor entirely.

I may just change out the blower & buy another resistor. Pointless to keep poofing $20 resistors in the process of troubleshooting.

ALSO - thanks so much for all the help. You obviously have alot of experience with this.

goatherder

Well, it appears you hit the proverbial nail. Actually there were two problems.

I installed a new blower fan and a resistor from Dorman. In the instructions for the resistor there was a statement about blowers that appear to be OK but are actually bad and drawing too much current... which burns out the resistor. New blower would spin freely...old blower was a bit sticky but still spun. Difference was maybe 25%. I ASSume this "a bit sticky" made the difference in the current draw and was taking out the resistor. So I installed both and I now have a properly functioning blower.

But I still had no Hvac switching action - only blowing out the defrost vents. However, I just installed a winch bumper and had this orb-like thing left over. WTF do I do with this? So I ended up mounting the thing onto the AC accumulator with hose clamps and then re-routed the vacuum lines to it. After that I started the Jeep and on a whim decided to check to see it there was vacuum on the orb. Nope, no vacuum.

So I traced the line back to the engine and pulled it off ... and the engine sped up and there was a hiss. Then I stuck the line in my mouth and sucked on it and got nothing. I noticed a check valve, so I pulled it loose and sucked on it and got one way but not the other. It's working...so I turned it around and reconnected everything and now I got HVAC controls. Probably got cruise control too, now that I think about it. Imagine that.

SO - if your heater controls don't work and neither does cruise control...see if somebody installed that vacuum check valve backwards. Trace the vacuum line from the cruise control servo back to the engine and the check valve is right where that line connects to the intake.

EDIT: Cruise control now works like a champ. Woo Hoo!

quedog

has anyone tried checking for voltage on the ground side, I have seen in the posts that everyone checks for 12v+, but has anyone checked from the ground (at the plug) to chasse.

reason I asked is after reading this, and having a issue with my blower motor running low speed all the time, I found 1.5 v going to ground, if I add a ground (to the ground wire) I get a big spark and also I get high speed fan.

could anyone tell me why I would be reading 1.5V on the ground wire to the fender on a 96 xj