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Discussion Starter · #1 ·
My AC is normally working fine but sometimes after driving the car with the AC on, for a while, the air blowing will be less & the cooling will also be much less. Any idea about the cause of this problem?
 

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Seek to understand,^Value
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I don't have a clue what it could be ... but I did a /air conditioning(F3) in the bestlinks for you and came up with this summary which 'might' be helpful to give you ideas ... especially the part about testing the AC system ...

How to learn about (1) and set up your air conditioning (1) (2) & how to replace the activated charcoal cabin air filter (1) (2) & what cabin filter to buy (1) (2) & cn90's inexpensive cabin filter retrofit (1) (2) (3) & cabin air filter implications for stinky gym sock AC odors (1) (2) (3) (4) & how to refill your A/C system for $20 (1) (2) (3) (4) & where to find your low pressure aircon recharge port (1) & what refrigerant PAG oil to use (1) (1) & R134a conversion information (1) (2) how to measure A C temperature (1) & how to diagnose A / C compressor knocking sounds (1) & air conditioner compressor replacement DIYs (1) or compressor rebuilds (1) or ac hose rebuilding services (1) & how to remove the IHKA air conditioning control panel to clean the circuit board (1) (2) (3) (4) with removal of MID, HVAC/IHKA, Business CD player (1), & dashboard trim (1) & how to remove the trim and bracket holding the MID & HVAC/IHKA panels (1) (2) or to replace the IHKA button (1) & how to check the IHKA sampling fan (1) & how to change OBC MID IHKA KTMP temperature from degrees Celcius to Fahrenheit (1) (2) (3) (4) (5) (6) (7) (8) & how to diagnose lack of HVAC/IHKA heater core heat with cooling system (auxiliary pump) at idle (1) & what is this thing (HVAC/IHKA solar sensor) in the middle of my dashboard by the windshield (1) (2) (3) (4) (5) (6).
 

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My AC is normally working fine but sometimes after driving the car with the AC on, for a while, the air blowing will be less & the cooling will also be much less. Any idea about the cause of this problem?
It appears you live in a very warm climate. None the less is it possible that the A/C gets the cabin down to the temperature you've set in the HVAC control and then automatically reduces the fan speed and cooling effect? This would be acting as BMW designed it; cool quickly then reduce cooling to just enough to maintain the set temperature. Your description of "for a while" sounds as though this might be the case.

Is the cooling effect disappearing while the cabin is still too warm for comfort?
Or have you pushed the "MAX" button, but cooling decreases? MAX is supposed to force the A/C into maximum cooling and fast fan indefinitely.

When the fan speed decreases, do you see the indicator bars in the HVAC display change too? This would be as designed. If there is no change in the display when fan speed changes, the FSU is suspect.

Regards
RDL
 

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2003 530i
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My AC is normally working fine but sometimes after driving the car with the AC on, for a while, the air blowing will be less & the cooling will also be much less. Any idea about the cause of this problem?
A second thought

I made an assumption that when you described "the air blowing will be less" that the fan slowed down. However, it is possible that air flow could be reduced if the evaporator iced up and thus blocked/reduced air flow out the vents, even though the fan is still on high speed.
Does the fan slow?

The A/C system is designed so that icing should not ever occur, i.e. that evaporator temperature is never less than ~3-4C. Unless that is, a part or parts are defective.
If so, you will need specialized equipment &/or an A/C expert to make repairs.

Regards
RDL
 

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Seek to understand,^Value
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I'd bet my left one the FSU is dying.
It doesn't sound like the classic FSU symptoms ... but, just in case, the OP will benefit from a quick /FSU(F3) in the bestlinks:

- What is the right brand of BMW E39 FSU (aka FSR) to purchase (1) (2) when your interior heating & air conditioning HVAC/IHKA blower motor goes haywire (1) (2) (3) (4) (5) (6) (7) (8) & how to repair your own final stage resistor including an autopsy & wiring diagram schematic (1) (2) and why a bad final stage unit will cause the battery to drain overnight (1) (2) (3) & how to isolate and replace the E39 blower motor (1) (2) (3) (4) & how not to replace the FSU (1)
 

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Discussion Starter · #8 ·
A second thought

I made an assumption that when you described "the air blowing will be less" that the fan slowed down. However, it is possible that air flow could be reduced if the evaporator iced up and thus blocked/reduced air flow out the vents, even though the fan is still on high speed.
Does the fan slow?

The A/C system is designed so that icing should not ever occur, i.e. that evaporator temperature is never less than ~3-4C. Unless that is, a part or parts are defective.
If so, you will need specialized equipment &/or an A/C expert to make repairs.

Regards
RDL
I think you are right, the fan is not slow but the air blowing is less.

I think the evaporator iced.
 
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