I have a 97 XJ with 4.0. I was driving down the hwy today and the ac was set to recirculate and then I smelt a rubber plastic burning smell. Soon after smoke started rolling out of the vents, so I pulled off and checked it out. Didn't immediately see any thing so I took it off of recirculate and drove on with no smoke. It hasn't smoked since but when driving home later the ac seemed to not be working. It just wouldn't get cold. Then i got home and when I went to test it every thing seemed to be working so I took apart everything that was half way quick and easy to check; such as the vacuum resistor, the blower motor resistor, almost every connection I could find, looked at the blower motor with out actually taking it out though, and found no signs of any thing.
I am at a loss of what to do, aside from taking the whole dash apart and just to keep looking. I must also mention that with the previous owner it did sit for mostly a month at a time but sometimes more.
Thanks in advance, and yes i did a lot of searching.

 

remove all covers, radio, glove box and drive w/o them. If you see smoke again, you'll find where.

 

I'm friends with svaldin, got all the pannels off and driving, AC is blowing cold and no smoky smell. Does anyone think that the Blower Relay could have gotten an acumulation of dust on it and possibly smoked from that? Could not see any signs of hot spots anywhere?

 

If it sat, that's normal I think. Mine did it for a couple weeks after sitting a few month's.

 

Any smoke from the vents is not normal. I had a '94 Explorer that actually caught fire due to some leaves that snuck in and got stuck on the resistor; bad day

Check your blower motor. There is a small rubber buffer that sits on the shaft of mine. It's possible that it shifted or something (leaf, twig, magic fairy shoe) got stuck and caused it to spin on the shaft and create the smoke.

 

Let me tell you my experience with this. Smoke out the vents was caused by rodents packing carpet insulation in the blower motor area. Then the blower blew the stuff on the resistor. Resistor heat caused the stuff to smolder. You said it sat for a while?

 

Yeah it has had 2000 miles put on it in the last 4 years, so it has done a good amount of sitting, but it was driven by an old lady at least once a month for very short distances. We have checked to see that the blower spins freely, and it does not appear to have crap in it. Wondering if it may be something in the heater core area. The smoke was a dark gray with a plastic melty goodness smell. We will check on the rubber buffer

 

Also noticed that the vacuum switch for the recirc is not adjusting?