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[Paulie]

I know I probably won't be needing it much seeing as how the weather has warmed up so nicely , but the heater motor only works at full speed. The wiring diagram shows a switched resistor network for controlling the speed which has no doubt burnt itself to a crisp. Does anyone know where the resistors live? Are they part of the switch assy, or the motor?
Of course, I could be barking up the wrong tree and have a wiring issue.

[MOCAJ]

take out your glovebox and the heater resistor is fixed to the bulkhead. it is a common fault 

[Arno]

On my 05 TJ the resistor pack sits at the bottom of cabin heater fan assembly, so take of the passenger's side kick panel  and you'll see it there, about the size of a matchbox

Mine had a few circuits rusted through..  I just patched it with 13A flex, and 2 years down the line its still working a treat   

[Paulie]

Nice, thanks chaps. 

[Paulie]

Well, I pulled the glove box out and all I could see there were fuses and relays. It's a '97 model by the way, shoulda said so in the first post. Guess I need to dig a bit deeper.

[Cockney Boy]

It's actually below the glovebox




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[Paulie]

picture.... thousand words and all that. Thanks C.B.

[Paulie]

For anyone who's interested and doesn't already know, the resistor network in question is protected by a thermal fuse, i.e. it blows when it gets too hot rather than when the current is too great. Mine got flustered by the wads of dried leaves and bugs clustered around it and blew. I couldn't find a suitable replacement so have fitted some 15A fuse wire in its place. I'm hoping the smoke from my shoes and carpet will alert me to any overheat issues I may encounter. Anyway, the heater now works fine on all settings. Thanks to all, 'specially Arno for his input.
P.

[Arno]

Nice one Paul, good to hear you got it working again!

[Mike2909]

For anyone who's interested and doesn't already know, the resistor network in question is protected by a thermal fuse, i.e. it blows when it gets too hot rather than when the current is too great. Mine got flustered by the wads of dried leaves and bugs clustered around it and blew. I couldn't find a suitable replacement so have fitted some 15A fuse wire in its place. I'm hoping the smoke from my shoes and carpet will alert me to any overheat issues I may encounter. Anyway, the heater now works fine on all settings. Thanks to all, 'specially Arno for his input.
P.

Did you just have to replace the fuse to get it working again or the resistor? I have the same problem that the fan only works on full speed.

[Paulie]

Hi Mike, I changed the thermal fuse. It looked a bit like a diode with blue ceramic ends. I couldn't find anything of a similar spec on t'internet, so I just soldered a bit of 15A household fuse wire in place. Obviously you no longer have the thermal protection, but the main fuse for the heater system is 25A. 15A should see you roight, but I would advise you check for leaf matter after the autumn. This was the cause of my original failure. Bits of leaf became lodged around the resistor network and prevented it from being cooled by air drawn through by the fan. Good luck with it, let us know how you get on.

[Ezz]

My TJ heater only works on full, I might pull it out the garage tomorrow and have a look....

[Mike2909]

Hi Mike, I changed the thermal fuse. It looked a bit like a diode with blue ceramic ends. I couldn't find anything of a similar spec on t'internet, so I just soldered a bit of 15A household fuse wire in place. Obviously you no longer have the thermal protection, but the main fuse for the heater system is 25A. 15A should see you roight, but I would advise you check for leaf matter after the autumn. This was the cause of my original failure. Bits of leaf became lodged around the resistor network and prevented it from being cooled by air drawn through by the fan. Good luck with it, let us know how you get on.

Thanks for the reply. Where was the thermal fuse positioned under the glove box? I will try and make the  fix tomorrow.

[Paulie]

Yes, its behind a black plastic kick panel below the glove box. Once that kick panel is out, which is a bit fiddly, you'll see a square-ish plug attached to the resistor pack. Pull the plug, it has a locking catch, undo the 2 diagonally opposed bolts and remove the resistor pack. Once out, you will see a vented metal guard around the resistors. Pull that off by straightening the tabs and you'll see the resistors and fuse inside. Cut out the fuse, leave the wire legs long and bend them into loops then solder the fuse wire between them. Sorted. 

[Mike2909]

You make it sound simple you have obviously never seen my soldering skills 

I will do my best and your info will have helped.

[Paulie]

Haha! It's no too difficult. Start by making sure you clean the tip of the iron when it's hot on a piece of old rag or something, then re-tin it with solder. Do this frequently to keep it clean. Get a smallish blob going on the end of the iron then use that to heat the parts you are going join. Then keep dabbing with the end of the solder roll on the joint. Once it's hot enough the solder will flow. Add solder from the roll but don't go mad. Do not move until the joint as cooled or you may get a dry joint- air inside between the parts. Make sure the solder is nice and shiny with a good fillet between the wires. If not, simply re-heat the joint till the solder melts and allow to cool again while holding it still. Try not to do this too often, as the solder will degrade and you will have to clean the joint off and start again with fresh solder.
Give me a shout if you need any more help.
Let me know how it goes.

[Mike2909]

I am going to start on it Saturday along with a whole list of jobs that need doing. Thanks for the info and I will definitely let you know how it goes.

[Arno]

Did you just have to replace the fuse to get it working again or the resistor? I have the same problem that the fan only works on full speed.

If you fan only works on full, it's your resistor pack thats gone..!

Take it out and have a look for any obvious issues, like a broken contacts etc.. If you know what u doing with a multimeter, test the various circuits, else replace the resistor pack

[Jonny Jeep]

I replaced a thermal fuse in one of brothers cars once. He wanted it working as he wanted to sell the car, and it was the only fault. The fan only ran on full and we found the fuse had failed. Got the replacement thermal fuse from maplin. As soon as the fan was turned on after the repair the car started to fill with smoke so we turned it off damn quick. I had a workmate with the same car so measured his amp draw on full which was 6 amps. My brothers was drawing ten. We just tapped the wires and ran them through to the engine bay where we fitted 50W resistors to handle the heat. No issues after that.

I've been thinking about my (97) TJ lately (all speeds still work fine) regarding debris build up and came across a panel filter on ebay. I though it would do the job of keeping debris out if fitted at the intake in the cowl. I have noticed the airflow seems slower when at high temp compared to cold. I may try and blow air back through the vents and heater core, or see if I can get a narrow vac attachment in there somehow to clear any dust/debris off the core. Here's the filter I found anyway, just needs trimming to shape to cover or sit in the inlet...

http://www.ebay.co.uk/itm/350635171655?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

[Mike2909]

I eventually had to change the resistor.Mine looked as if it has been left in water for a few years. Some of the elements were broken off and the rust was one solid rusted mass.
I bought a replacement removed and fitted in 10 minutes and running smoothly now.