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  #1  
Old 05-22-2024, 03:21 AM
jac jac is offline
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A/C not blowing, Aux Fan OK

Just when summer is starting... The A/C decides to stop working... sigh...

Basically, the display comes on and you can change the temperature setting up and down, as well as the fan speed. However, other than changing the settings in the display nothing happens. Absolutely no air is coming out of any of the vents and the Aux Fan does not run either.

I tested the Aux Fan by removing the connector off the a/c pressure line while the car was running and while the A/C settings were set to high. That caused the aux FAN to come on and to spin at full speed. So it isn't the aux FAN.

I also connected INPA and also BMW Scanner 1.4, and these only reported an error for the AUC sensor.

I would appreciate it if anyone could help me with pointers of what to check next. I am thinking the a/c system has no "r134a" but I would like to rule out other stuff first before taking it to an A/C shop.

Thanks!
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  #2  
Old 05-22-2024, 07:24 AM
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Yes.. I think you need to attach a set of AC gauges and see what you have.
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  #3  
Old 05-22-2024, 07:53 AM
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A/C work is not as complicated once you understand how to add and check R134. Remove the low and high side port covers. Do it while it's warm. Do you see evidence of a leak? The most common failure for old A/C systems is valve cores. A shop will swap everything and sometimes not even change the valve cores. I've seen it. I've replaced more valve cores on friends cars than entire A/C system rebuilds. A cheap vacuum and hoses are sufficient to vacuum and charge. For 1/3 or less of a shop price, you can buy equipment and fix it yourself. I had a great teacher show me the ropes to A/C work. I wanted to learn after one shop charged me $600+ for work back in '98.

For novices, I tell them to buy the expensive can of R134 with a hose. The dial indicator will keep you from adding too much R134. Connect it to the low side. If it charges up and leaks out, the valve cores are likely bad. A simple tool is used to replace valve cores.
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Old 05-22-2024, 09:26 AM
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Quote:
Absolutely no air is coming out of any of the vents
So the fan isn't working only with A/C on ???
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Old 05-22-2024, 10:23 AM
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@80stech: Yes, correct no air blowing in the cabin and the Aux Fan does not move. I have only been able to make the Aux Fan move by unplugging the electrical plug on the A/C pressure line.

On INPA, I was able to move the stepper motor for the various internal flaps (I could hear them moving). But I was not able to do anything else on INPA, though I tried. It had a button in the A/C section to turn on the "blower" but that did not do anything.

@X5Chemist: and EFFDuration: Thanks! I will try the "newbie" approach you described :-)
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Old 05-22-2024, 11:27 AM
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A/C not blowing, Aux Fan OK

No air blowing means the HVAC cabin blower is not spinning is that what you are saying?

I would use scan tool to command the blower on make sure it's working and go from there.

Often the FSU will have a dirty connection and unplugging and re plugging will get the blower spinning. There's also a test you can short the correct pins on the FSU plug and get the fan to spin full speed.

Confirm you are saying the internal blower is not spinning. The scan software should also show if the AC compressor is engaging.

If you drive so the condenser gets air flow and request AC the evaporator should get cold (measure with software) and the pipes under the hood will get hot/cold even if the blower isn't getting the cold air pushed into the cabin.

FSU is orders of magnitude easier then AC recharge (which also is not that bad)

The "blower" test doing nothing says most likely your FSU not functional. Very recent thread described the exact pins on the FSU connector to jumper to test the blower.

If that works you should be able to run AC and get cold though the HVAC brain may not allow the compressor to engage if it can't detect the FSU.
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Old 05-22-2024, 02:03 PM
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@AndrewWinn: Yes, correct no air whatsoever comes out of the vents in the front of the cabin, so HVAC cabin blower not coming on. I have checked all the fuses, including the 50 AMP fuse and they are all good.

I did check the rear blower just now, and the rear blower did come on and air was blowing out of those 2 rear vents.

I let it run that way (with the engine running and the rear unit blowing to its max) to try to refill the A/C system with one of those cheap kits with a gauge on top of the can. As I was doing that, I noticed that the A/C compressor gets engaged off and on. It engages for about 10 seconds then off for, say 30 to 50 seconds, and then engages again for 10 seconds, and so on...

As it was doing that, I also saw that the Aux Fan was spinning now. That's a small win :-)

When you say "the scanner software should show if compressor is engaging", which scanner software are you referring to? INPA? I did not see anything about the compressor in the INPA screens. :-(

I did use INPA to command the blower to come on but it did NOT come on. So, I will go looking for the thread you mentioned about manually engaging it via the FSU connector.

BTW, I am not familiar with the term FSU, what does it mean?
[Edit] FSU = Final Stage Unit, I had heard about that, just not the acronym! :-). Also, found the thread for testing the connector. Gonna do that as soon as this darn storm passes.


Thanks!
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Last edited by jac; 05-22-2024 at 02:13 PM.
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  #8  
Old 05-22-2024, 02:45 PM
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A/C not blowing, Aux Fan OK

People erroneously refer to the FSU as the final stage resistor FSR but that prob went away in the 80s or 90s kind of like taking about the carburator.

The back blower uses a separate blower and FSU. You need to test your blower. Find the method using the pin jumper solution you can find on xoutpost.

I don't have/use the BMW software. I used a foxwell scanner that I can for example monitor the evaporator temp and test the blower by commanding it on 80% speed for example.

Somebody here knows if inpa etc can be used in the same way but it's most likely FSU and some chance it's the blower motor but you want it to be FSU much easier solution.
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Old 05-22-2024, 07:06 PM
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Thanks AndrewWynn! The issue indeed turned out to be related to the FSU.

I did the test shorting pins 5->2 and 4->1 on the FSU connector and the blower came on right away.

I then tried out connecting the FSU and it worked just fine! The blower came on... So, not sure if the FSU needed to be disconnected for a bit (it looks like it is constantly fed +12v) or if it was the FSU connector not being seated properly or having some rust.

So, I put it back together and it is all good for now. If it happens again I likely will just replace the FSU.

Thank you all so much for all your help. You guys are awesome!
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Old 05-22-2024, 07:09 PM
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They self destruct from heat and the fact they are always powered (#1 parasitic drain issue). I'd order one to have handy once they start to show signs they don't usually last very long.

Are the cooling fins cylinders or cones? If cones very overdue for replacement.
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