I'm trying to find out why my A/C vents work intermittently. I notice frequently I lose airflow from the dash vents to the floor vents. It seems it happens under engine load but not always. I tried trouble shooting the vacuum lines but none of the lines or tees were broken, disconnected or kinked. Also the compressor quit working while I was stuck in traffic. It came back to life after driving normal speeds for about 15 minutes.
I'm stumped.

 

The heater doing this as well?

 

I didn't try it. It's been too warm.

 

I have this exact same problem. Started with my heater doing it and ac worked fine. Then ac started doing it. Been trying to figure it out for a while.

I've heard anything from check the vacuum at where the hoses connects to the firewall. To it's a bad control switch or cracked reservoir but no luck yet.

 

vacuum leak. had this problem couple times, last time everything under hood looked perfect, upon second look a line popped off.

 

Mine did the same thing. It was a vacuum line. Check the hard plastic lines under the hood on the passenger side in the corner of the fender and firewall. Mine was the white one. It had dry rotted.

 

The only thing I couldn't check were where the two lines go into the plastic conduit. It's taped up. I was assuming those lines are in good shape since the other exposed lines are still good. My one suspicion is the plastic vacuum box attached to evaporator cover is leaking. It doesn't look like it's replaceable.

 

So my lines look good even going through the fire wall. What else could it be or can I check?

 

Many times you won't be able to see that the white rigid vacuum line is leaking. And it seems to go bad everywhere along its length, even where it runs through the loom. It is usually the problem and just needs to be replaced.

 

I wish I had a Mitivac so I could pull some vacuum through those lines. I wish I kept the extra lines when I bought the engine that's currently in it. I sold all the old stuff I didn't think I'd need.
Thanks for the suggestion Snowdog.

 

I have a similar problem but the air comes out defrost no matter what is selected and then randomly comes through the vents.