Final Stage Resistor - A/C

[wcmaness]

I think this is my problem - but before I take off the dash I want to be sure. Here's my situation: The A/C blows cold when I need it to, and all the A/C elements seem to work fine except for the blower. I can set it on high, and still only get a moderate flow of air from my A/C. However, as I approach the set temperatire - say 72 degrees, just as I get to 72 (I think) then it blows hard and strong. I want that strong air flow all the time (I'm in Texas and it's hit over 100 for a few weeks now) no matter what the temp setting is at. It makes no difference if I have the fan set on high or medium range at the moment) I discovered that if I lower the temp to say 68 while it's blowing hard, then it reduces to the previous moderate/meager air flow.

So - does it sound like my final stage resistor is the culprit?

[Mayorchuck]

Is the ambient temperature reading correctly on the panel? I know I have had issues in the past where the outside temp was not all that hot but it was humid so I tried to crank the air but it would not go. Ice or Q explained how it affects the HVAC but I don't remember exactly how it worked. The system didn't think I needed the cool air so I didn't get it!

[Edwin NL]

MAX AC doesn't help?
Adjusting fan speed to max?

[wcmaness]

Setting it to Max only assures I will never get the full airflow - because it never reaches that 60 degree temp (at least not in the summer). Setting the fan speed to max does nothing - until I hit the temp set. The temps are correct.

[SirReal63]

Mine does the same, interested in the fix. It has been extremely hot here in TX this summer. Mine does blow hard after about 15 minutes, but getting the initial heat out of the car is fun.

[wcmaness]

I've got a new rsistor in hand. I plan to replace it this weekend. One last bit of info to confirm the cause = When I have it on high all the way cool, if I push the button to turn off the A/C, the air comes out super strong. When I push it again to turn the a/c on, it drops back down. Still think it's the resistor?

[blacksport]

I think this is my problem - but before I take off the dash I want to be sure. Here's my situation: The A/C blows cold when I need it to, and all the A/C elements seem to work fine except for the blower. I can set it on high, and still only get a moderate flow of air from my A/C. However, as I approach the set temperatire - say 72 degrees, just as I get to 72 (I think) then it blows hard and strong. I want that strong air flow all the time (I'm in Texas and it's hit over 100 for a few weeks now) no matter what the temp setting is at. It makes no difference if I have the fan set on high or medium range at the moment) I discovered that if I lower the temp to say 68 while it's blowing hard, then it reduces to the previous moderate/meager air flow.

So - does it sound like my final stage resistor is the culprit?


When I bought my car 3 years ago it kind of acted like this. I just didnt seem to be getting full airflow out of the vents even when fan was set HIGH, even on MAX. But then occasionally I'd get like a "burst" of air out of the vents for awhile and think, now why can't I always get that volume of air out of the vents all the time ?? Why does that only happen occasionally ? I never related mine to it approaching the set temp, maybe thats when mine was happening but dont know.

Only thing I did was clean the small air filters under the dash on drivers and pass side. They were extremely dirty. I just cleaned them with soap and water, let them dry, and then put the filter material back in the frame and then put them back up inside the dash.

After that, the volume of air was much higher and I was satisfied with it and never again has it ever given me those "bursts of air", it just stays on a comfortable air flow all the time now.

I was surprised cleaning the filters fixed my problem, doesnt seem like the bursts of air I was occassionally getting could be related to clogged filters and maybe it wasnt. All I know is that my air flow problem disappeared after cleaning the filters.

If you havent cleaned your filters, give it a shot, not that hard to do, took me about 45 minutes to an hour for both sides. You dont need to replace the material, you can wash and dry and reuse the original stuff. Recheck airflow volume after you clean them. Check E38.ORG for instructions

What does it do when you set your temp and then press both "Auto" buttons on both sides of the a/c controls ??

[SirReal63]

Thanks Blacksport...and to Edwin. I just pulled the passenger side inside air filter and it looked like it was covered in mud. I separated the cage and added some polyester batting in it's place. The initial response was great, I will do the driver side tomorrow.

Edwin's excellent write up on it.
http://www.bimmerboard.com/forums/posts/348259

I would do this even if it didn't change the fan output, when on MAX is needs to pull air from the cabin and recirculate it, if it is clogged, it is a restriction and you are not getting maximum air flow.

[wcmaness]

Now that makes a lot of sense. I'm going to try that first - I'll let you know the result. I'm surprised this isn't identified by the dealer as a possible cause.

[SirReal63]

I just did the driver side and I now get full air flow when set to recirc or MAX. If you have never done this simple filter change...do it, it is easy and the airflow you have been missing will surprise you.

[blacksport]

I just did the driver side and I now get full air flow when set to recirc or MAX. If you have never done this simple filter change...do it, it is easy and the airflow you have been missing will surprise you.


I'm glad that helped but if I understand, it only helped you in Recirc and Max mode, you're still not happy with flow of air when its NOT in Recirc or Max ??

[SirReal63]

With the temps well over 100 since I got the car in June...it rarely ever sees anything but MAX. Once the cabin has been cooled off and I take it off MAX, the normal lower fan speeds work fine. Obviously this is not a replacement for a malfunctioning final stage resistor, but it can help explain why air flow is not up to par when on MAX. Once my car has cooled off I just put it on auto and have the fan speed in the middle and the temp at 72 and it keeps the car cool. I never tried anything other than MAX for high fan speed. I will in a bit, I have a Dr appt to drive to and will test it out.

[Qsilver7]

Remember too that if you have the AUC button pressed (auto recirculate) where the left green LED is illuminated...the HVAC system is going back in forth between fresh air and recirculated air.

So if the interior recirculation filters have NOT been changed...then this could be the reason that the air velocity is diminished and that the air appears to fluctuate from a moderate flow of air to seemingly restricted flow of air.


http://www.bimmerboard.com/members/q/original/AUC%20Recirculating%20Air%20Button%20Operation.jpg
http://www.bimmerboard.com/members/q/original/AUC%20Recirculating%20Air%20Sensor%20Operation.jpg

http://www.bimmerboard.com/members/q/original/E38%20AUC%20Climate%20Recirculate.jpg

[SirReal63]

Q it makes perfect sense. I did my little test drive, all systems are functionally correctly. I have complete control over the fans and air volume is greatly increased. Before, on MAX it would take (interestingly enough) about 10-15 minutes before the fan came on high speed. Now it does it instantly. I am attributing the issues I had with the clogged cabin air filters.

This is the drivers side, it looked a little better than the passenger side.
http://img.photobucket.com/albums/v362/sirreal63/Car%20Shots/003-1.jpg

I did not clean them, I replaced the filter with some polyester batting that I use for my reef tank for mechanical filtration when needed.

[wcmaness]

WOW - that was it. Mine were totally blocked. I am shocked the dealer did not know about this. In fact - when I went to get the filters, the service manager told me that in the last 25 years, he doesn't remember ever replacing these. They just had been telling me that the A/C generally was not good in Texas, and that probably by final stage resistor was bad. Thanks a million. All is well now with my A/C air flow.

http://i392.photobucket.com/albums/pp5/wcmaness/filter1.jpg

[SirReal63]

I am glad that is all it was. I am pleased that it was such a simple fix for me as well. I wonder how many of our cars are running around with totally clogged cabin filters? I find the A/C perfectly adequate for our hot climate...at least now. :-)

[blacksport]

WOW - that was it. Mine were totally blocked. I am shocked the dealer did not know about this. In fact - when I went to get the filters, the service manager told me that in the last 25 years, he doesn't remember ever replacing these. They just had been telling me that the A/C generally was not good in Texas, and that probably by final stage resistor was bad. Thanks a million. All is well now with my A/C air flow.

http://i392.photobucket.com/albums/pp5/wcmaness/filter1.jpg

Thats good, glad that worked for you like it worked for me. Sure beats tearing out the whole dash to get to the blower doesnt it ?

[wcmaness]

Amen to that.

[IcemanBHE]

Avoid that dealer. Its part of the maintenance routine.