Wait... so you have the AC on, it stops blowing, you turn the AC off but leave the vents on/blowing and then the airflow resumes? Does the blower fan motor hold steady speed but just the airflow stop?

Here is what happens;

On initial startup air works fine. Blows cold and out of all vents. On trips over about an half hour (typically associated with highway driving) the vents will just flat out stop all of a sudden. Keep in mind there is no fluctuation, they just flat out quit. When I try to turn the vent speed up, I hear sound increasing, but the air flow does not. When this happens, I simply push the a/c button to turn it off (keeping all fan settings as is). In other words, vent is still on. After a few minutes (maybe 3-10 minutes), the vents will resume blowing again. When this happens, I can then push the a/c button to turn it back on and it will work again for a while (say about 10-25 minutes), until I have to repeat this process.

This rarely happens on short in-town trips. One thing I have noticed is that after consecutive shorter trips where the air has been in and out of use for a decent amount of time in one day, the air out of the drivers side and middle-left vents is colder than the middle-right and passenger side vent.

Also, note that I had the fsr, high side service port and IHKA control unit replaced 2 years (20k miles) ago. The system was recharged with that service.

I do know that I am probably due to replace the microfilter. It has been in for about 35k miles.

So the blower keeps blowing, but the air stops coming out of the vents... then turning off the compressor for a while allows it to blow again. It almost sounds like the evaporator is freezing up. But usually with that the air flow slows then stops rather than stop all of a sudden. Something to look into though.

What temperature does the air blow out of the vents when it is working properly?

I was thinking the evaporator was freezing as well, but it literally only takes a few minutes before it starts working again. Wouldn't it take longer if it were frozen over?

Also, how could the blower actually be blowing if no air is coming out of the vents? Wouldn't it be more like blower on = air movement, blower off = no air movement? When I say the air stops, I don't just mean the a/c stops. I mean there is literally no air movement coming out of the vents at all. Cold or warmer vent air. Then when I turn off the compressor for a few minutes, warmer vent air starts flowing again. After the vent air movement resumes, if I turn the compressor back on, it blows cold a/c again. I have to repeat this process over and over if I am on a long trip.

Earlier, when I said that I heard sound increasing when I manually turned up the fan speed, the noise wasn't necessarily coming from the main dash vents. It could be coming from the back, other areas, etc. Sorry if that was confusing.

Overall, it sounds like my first actions are to replace the microfilter and make sure the system if fully charged. Then look at the fsr connection.

I am not sure what temperature the air is coming out of hte vents. I have no way to test this at home. I will have the shop that checks the system give me a before and after reading if they have to charge it.

The microfilter won't cause the issues you are experiencing, but is still worth changing from a maintenance standpoint. I guess this may be a case that needs to be diagnosed in person with all the proper resources at hand...

Still worth the wires shake test when it is acting up though, that could still show if that is the issue or not.

Yeah, I am going to try that. Let me ask you one last thing, if the fsr connection is indeed an issue, does it seem odd to you that it only happens when the a/c has been on for a half hour or more? If this is the issue, wouldn't it sometimes act up sooner during short trips?

Don't know an A/C yet, but even with the heater on, Rear fan has very high sound and no air is coming in. when off it stops eventually... I think this is rear vent problem only, have to get it checked.

What I've seen once or twice is that the connection is just bad enough with a higher resistance that over some time it gets hot and causes itself to get worse, but when cooled off a bit starts working again... It's still a longshot, but worth trying since it doesn't cost anything but a few minutes of time.

If you open the center console and pop the storage bin out you can make sure the duct to the rear vents is still attached properly. The bin is tight at first, but does just snap out straight up. Once you are looking in there with the bin out it is pretty straight forward to figure out.

sounds like a common problem almost everywhere on the old e53. it has happened to the elect connections at my front 2 signal lights, all my rear & brake lights, insturment panel display, .... good thing is that all it takes is a piece of sandpaper, a can of contact spray and some soldering do get the job done. :thumbup: