Smoke out dash vent with AC on
 

2000 Accord 4cyl. 150k miles

My daughter is on a road trip and called me yesterday on the road. She started getting smoke from her dash vents only when the AC is on. It goes away when she turns the AC off. She said it hadn't been cooling as well for a couple days and thought it might also be a little noisier.

She's at my sister's place now and my brother in law is looking at it. He can't find anything unusual although he says it seems like it should be cooler.

I searched the subject and read some earlier posts on this subject but didn't find any that really matched her conditions or any that had any resolution.

Any ideas what might be causing this. She said it kind of smelled like burnt rubber. My bro in law said all the belts look perfect.

There are only two kinds of smoke that can come out of the vents on an a/c system. Water vapor or Freon. Does she get "smoke" immediately after turning on the a/c? Water vapor will have a slight smell, but R-134a will have a stronger chemical smell.

I will talk to her more about it on Monday. She had been driving for a couple hours in 100+ heat on the interstate when it began. It stops when she turns off the AC. I'll check if she also turned the fan off.

What condition would create water vapor? She was driving in a hot dry environment.

Normally that happens in a hot HUMID environment. The AC is condensing water from the humid air.

I've observed smoke from the AC vents only once - in my son's '86 Prelude. 'White' smoke, no particular odor.
I immediately guessed it was a freon leak (in the evaporator ?) which would cool the air super cold -
freon cools when it expands; so it was condensing water in the flowing air stream. Dry climate - 9" rain/yr.

Sure enough, the AC unit never cooled after that although the fan blew.
Didn't repair the AC, drove car to the ground.

Agreed... It's the same thing as when you exhale outside in the cool weather. If the A/C is still functioning, it's not refrigerant, there isn't much in there really.

If this is troublesome to your daughter, the effect is lessened if you turn on "recirculate". Then the air being drawn into the system is from inside, and normally carries less moisture as the interior cools down.

Tell her it's the same thing as the "fog" seems to come off a bowl of ice cream. Doesn't prevent people from eating ice cream when it's hot & humid outside...

If it were actually leaking refrigerant, that leak would not stop when you switch off the AC. It wouldn't stop leaking until all the refrigerant is gone, then the AC wouldn't cool any more.

Re-reading the first post, I have another thought.

When the refrigerant is low, the system operates at a lower temperature. But even tho the temperature is lower, it has LESS cooling power. That could be a very slow leak that took a year to get to this point.

The way to fix THAT problem is to have an AC shop measure high & low -side pressures & add refrigerant if needed. Possibly add dye to the refrigerant so they can see where it's leaking.

OK I got more information now that she's home. She said it kind of smelled like burnt rubber. Very faint though. The AC is working most of the time but sometimes it blows warm air then it will work again the next time she starts it. She hasn't had anymore of the smoke/vapor since that first time.

Have the pressures tested (high and low) to make sure the system is properly charged.

Next, I'd check for codes from the HVAC system. Two type on this gen Accord, manual and auto HVAC - does it have a knob you turn from hot to cold or is there a temp read out you can set?

To Jim's point, a low charge can actually cause the evap to freeze up.

If everything tests/checks out, can't hurt to change the cabin air filter and I would check the ac drain hose to be sure it is not clogged. I cheat and use my shop vav (wet setting) and vac it from the hose.

I had her bring it in today. They said it was overcharged and that it was freezing up. They evacuated it, recharged to the correct charge and we will see. It worked while she was driving it around this afternoon.

We've only had the car since January and that was the longest she's ever driven it with the air on. I guess it's been fine since she got back from her trip - shorter runs around town so the freezing up part seems to make sense. I kind of figured it was some sort of vapor as she said it didn't accumulate in the cabin like smoke would. I had it in for service for her a month ago and had them change the cabin filter as I didn't know how old it was. Checking the drain tube is also a good idea. We'll address that this weekend.

I haven't gone through the folder of receipts I have on it yet to see if it's ever had the air worked on before.

Thanks to everyone for your comments and suggestions. Ultimately getting it in and looked at and the pressure tested was the best thing but you all gave me a better understanding of the system. I will post again on this thread if we have any additional trouble to keep everyone updated.

Thanks again. Great forum!

You should check whether compressor is cycling on/off under control of thermostat. If compressor runs continuously, it is likely to freeze up and white vapor (water fog) from vents is result. You may need a new thermistor or thermostat.

Here in Houstion w/ high humidity, this temp control is essential to prevent freezeup, but even at low humidity if compressor never cuts out, evap temp will get very cold and freezeup is likely.

good luck

I assume you can run it and listen for it to cut in and out?

While driving it may be difficult to perceive if compressor is on/off. You may need to observe a stopped vehicle w/ hood raised to check.

good luck