Intermittent Engine Air in the AC/Vent
 

A couple of times now I've had intermittent hot air (feels like engine air) blow from the vent/ac. It's usually gone in less than a minute, but highly annoying. It happened this morning when I shifted from 3rd to 4th gear. I'm guessing there's a hose loose somewhere.

Anyone else had this issue? Any place in the engine I should look first when I investigate?

Thanks,

Matt

Had it happen again on the way home. I reved to 8k in first, sat at around 5-6k in second before reving up again. In second was when it happened.

Set the air to recycle and see if the problem persists. If it doesn't, seems like it's a problem somewhere along the external air intake route. For what it's worth, have not read about this problem before on this forum.

Ok, I'll try that.

Yeah, I searched and found nothing - was a bit surprised! I figured that every issue with these cars was already hashed out over the last 5 years! :lol2:

All right, so today I got some more information. I was riding down the highway in 6th gear, 70mph, with no air on, and the air set to recycle. Suddenly, the air went very hot. I pressed the ac button - still hot. Pressed it again (off), then on again. Finally, cold air. Rode for a while with the air on, and it stayed on. I turned the air off and after a few minutes the hot air came back.

So perhaps it is not to do with the external air intake. I've never experienced it with the ac on, either. I really haven't ridden with the vent on the last month, so I really can't say it happens infrequently when the vent is on - seems pretty frequent.

Same Problem =(
 

Now that we are in the middle of the first heat wave of the summer in the NorthEast, i too, have noticed the same problem. 2004 rx8, that i've owned for 4 years, 40,000mi, never noticed anything like it before. I know that when the engine is under high load, it will switch off the a/c as needed, but it seems to be doing it alot, when not under load. If i am running in vent mode, and its doing it alot, and i switch to recirculation, it seems to go away for a while, and vice-versa. Also, if i have the temp knob all the way cold, and the a/c starts blowing hot, i click it one notch warmer and the a/c goes back on for a bit. One other thing i have noticed, i can actually hear the airflow change when the AC goes off, and it switches to engine hot air. It seems like something the car is doing automatically for some reason, so i dont want to keep fiddling with buttons to make it come back on, if its turning off for some sort of reason. Anyone have any insight yet?

Some additional info:
I was incorrect earlier when i said hitting the recycle/vent button made the a/c come back on, it doesnt. The only way it comes back on is adjusting the temp knob for some reason. Its not dependent on the A/C either, on my way home, i ran the a/c enough to cool down the car, and then switched it off and just used recycle to circulate the air, was sitting at a stop light, nice and cool, and it switched to blowing hot engine air. I'm completely stumped.

A common problem for the HVAC systems in these cars is to have the controller dial go bad. Some people have had luck with disassembling the unit and putting it back together, and others have had them replaced under warranty.

A faulty temperature knob could cause the heating/cooling settings to not work at all, or possibly change randomly.

It normal for it to cycle from cold to hot.

In this car!

The A/C will shut off during extreme load on the engine. High RPM, high load. This is normal. Mine turns hot when the car is about to overheat too.

has to some more info on this. My car does it in regular traffic, not high load conditons!

I am going to second this. There seems to be a problem with the HVAC Control Unit doing random things. It happened to me and I am replacing the unit tomorrow. Some of the symptoms that I have experienced are HOT air when set to cold, COLD air when set to hot, and basically at random times it would switch and work the way it was supposed to for a while then switch back and do the opposite of what it should be doing.

One way to diagnose this is to set the fan to 4, turn the temp knob all the way to the coolest position and try to keep turning it past where it stops (use force, but don't be a fucking gorilla with it). This will usually kick the AC back on and as long as it is held there it will blow cold like it should. If that works then you know that there is nothing wrong with the AC as it does cool the air when it is on. This means that there is a problem with the HVAC Controls and they will probably need to be replaced.

Anyways, hope this helps.

agree with Easy, the A/C compressor cycles on and off in odd ways, i actually think it completely cuts out under load at very high rpms..

PLUS... turn the AC on full&recirc, hold you hadn in front of it.... now slowly climb from idle to redline feeling the AC the whole way....

the AC is noticably coldest in the 4000-6000 rpm range, below and above that its out of its peak efficiency range...