Having intermittent airflow issue with A/C

RenaissanceMan · #1 08-12-2016, 05:16 PM

Hi-

My 3.0 X5 has been starting some intermittent behavior with the A/C blower. With the A/C running, occasionally the volume of airflow will suddenly diminish. After a couple of minutes, it returns to normal. It does this regardless of what outside air/recirculatory setting I have selected. What's strange is that it doesn't sound like the blower slows down... Almost as if a flap has suddenly closed for a moment or something, but I'm just speculating. Anyone have any ideas? Thanks in advance-

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Rosssavage · #2 08-12-2016, 05:31 PM

Usual culprit is the final stage resistor (FSR or 'hedgehog').

Well documented, fairly straightforward diy.

RenaissanceMan · #3 08-12-2016, 10:02 PM

Quote:

Originally Posted by Rosssavage

Usual culprit is the final stage resistor (FSR or 'hedgehog').

Well documented, fairly straightforward diy.

Thanks for the info! I'll check it out. Hoping there is a testing procedure for it in my Bentley.

Rosssavage · #4 08-13-2016, 03:19 AM

Replacement diy:

BMW X5 - How to Replace the Final Stage Resistor

I've done this on my old e46 but not the x5 yet... It is fiddly, but only because access is awkward. Very common failure and leads to all sorts of weird hvac behaviour... Good luck!

bmw540san · #5 08-13-2016, 08:49 AM

If you hear blower still blowing hard but little or no air is coming out, it's NOT the blower resistor.
When blower is going, the flow is erratic and there is sound from inside as something is blocking the flow.
The cause is ice build up on the outside of evaporator core and the simple test to prove is to turn off the A/C, keep the blower on and make sure the air is set to OUTSIDE not to REC.
In matter of minutes you should restore full blower flow.
I'm not sure the about the cause but low freon can be one.

RenaissanceMan · #6 08-13-2016, 09:55 AM

Quote:

Originally Posted by bmw540san

If you hear blower still blowing hard but little or no air is coming out, it's NOT the blower resistor.
When blower is going, the flow is erratic and there is sound from inside as something is blocking the flow.
The cause is ice build up on the outside of evaporator core and the simple test to prove is to turn off the A/C, keep the blower on and make sure the air is set to OUTSIDE not to REC.
In matter of minutes you should restore full blower flow.
I'm not sure the about the cause but low freon can be one.

Thanks for the insight! One question though: If the evap core was iced-over, wouldn't the buildup remain along with the restricted airflow if I left the A/C compressor on? As I mentioned originally, flow is restored after a minute or so (sometimes longer) with the A/C running, so I'm not sure if that's indicative of a different issue?

upallnight · #7 08-13-2016, 10:08 AM

Quote:

Originally Posted by RenaissanceMan

Thanks for the insight! One question though: If the evap core was iced-over, wouldn't the buildup remain along with the restricted airflow if I left the A/C compressor on? As I mentioned originally, flow is restored after a minute or so (sometimes longer) with the A/C running, so I'm not sure if that's indicative of a different issue?

The AC switch maybe on, but it is the computer that determines if the compressor is engaged or not. Best to install a set of gauges and see what type of pressure readings you have for the low side and high side in the system. Anything else is just a guess.

RenaissanceMan · #8 08-13-2016, 01:55 PM

Quote:

Originally Posted by upallnight

The AC switch maybe on, but it is the computer that determines if the compressor is engaged or not. Best to install a set of gauges and see what type of pressure readings you have for the low side and high side in the system. Anything else is just a guess.

Can anyone tell me what the pressures should be? Thanks-

TiAgX5 · #9 08-13-2016, 02:20 PM

Per the OPs initial post, "occasionally the volume of airflow will suddenly diminish".

This symptom is not caused by icing or compressor disengagement.

Icing will cause a gradual loss of airflow (and a long low flow time cycle).

Compressor disengagement will usually not effect flow at all, only warmer air flowing.

Sudden loss of airflow symptom is classic FSR malfunction condition.

RenaissanceMan · #10 08-21-2016, 02:11 PM

Ok, so I wanted to share my results. Just put in the new FSR, and lo and behold, the behavior was the same. However..... I did some experimentation and I found that the temperature setting had an effect on all of this. For instance, when I first tested I had the temp controls set to 68 degrees. Same thing happened. A/C ran for a while and then flow seemed to diminish some with no change in temperature. I then lowered the controls to 60 degrees and flow was restored. Again, as in my initial description of the issue, it sounds like the fan speed stays the same but some flap has opened up, resulting in less volume of airflow... Now I don't know if this was just a coincidence, but I have never noticed this kind of a change before in all of the years owning my X5. Is it normal behavior for the flow to vary some on and off if you have the temp settings set higher than full cold? Is there a flap or valve that switches on and off accordingly? Sorry if this seems like a dumb question but I'm a bit confused by the behavior. Thanks-

EDIT... I should also add that the compressor stays engaged during all of this, with the vent temps essentially staying the same.

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