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Thread: A/C and heater weirdness

  1. #1
    Join Date
    Feb 2016
    Location
    Alexandria, Va.
    Posts
    25
    My Cars
    2000 M Roadster

    A/C and heater weirdness

    BLUF: Both the A/C and heater have sub-par performance idling at stoplights low-speeds etc. but work great when driving down the road.

    Last winter I noticed that my heater output was less than stellar at low speed but on the freeway it pumped out heat just fine, this summer I've noticed the same is true of the A/C.
    At 60mph, it cools pretty darn well actually and the aux fan up front appears to be working too. Any thoughts about stuff to check?
    The fan switch and cabin fan work well too.

    Thanks -

  2. #2
    Join Date
    Apr 2005
    Location
    Lawrenceville, GA
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    11,860
    My Cars
    4 BMWs.
    Quote Originally Posted by Serotta View Post
    BLUF: Both the A/C and heater have sub-par performance idling at stoplights low-speeds etc. but work great when driving down the road. Last winter I noticed that my heater output was less than stellar at low speed but on the freeway it pumped out heat just fine, this summer I've noticed the same is true of the A/C. At 60mph, it cools pretty darn well actually and the aux fan up front appears to be working too. Any thoughts about stuff to check? The fan switch and cabin fan work well too. Thanks -
    Well for the heater, you need the coolant system bled. I had the same problem on mine. As for the AC you might want to make sure the fan clutch and or electric fan is working.
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  3. #3
    Join Date
    Jan 2011
    Location
    Boise, ID
    Posts
    2
    My Cars
    1987 BMW 325e
    I know this thread is over a year old, but just wondered if there was a solution. I'm having the same issue with my 2001 roadster 3.0. Had the heater valve replaced this week. While driving at 30+ mph, the air blows at about 130 degrees. At idle, its dropped to as low as about 105.

    By comparison, I did the same test on my wife's 2005 mazda 3 hatchback. Her heater topped out at about 185 degrees and would only drop to about 176 at most. This, after about 4 minutes of idling.

    I'm curious - is what max temp should I expect on my car? I originally thought 130-135 seemed ok, but now wondering after I see how hot my wife's is.

    Even if 130-135 degrees is a reasonable high end temp, I can't help but think that a nearly 20 degree drop during a 2-minute wait at a light seems a bit much. Anyone else have similar experience?

    If what I'm experiencing is not normal, anyone have a suggestion on a next thing to look at?

  4. #4
    Join Date
    Jan 2011
    Location
    Boise, ID
    Posts
    2
    My Cars
    1987 BMW 325e
    Should have mentioned that, assuming my temp gauge is working correctly, the car appears to be operating at an appropriate temp with the gauge pointing basically at 12:00 when fully warmed up. I don't think my tstat is bad.

  5. #5
    Join Date
    Dec 2007
    Location
    Great Dismal Swamp
    Posts
    16,026
    My Cars
    E36/7 E36/8x2 E46 F25
    Low on coolant and a misadjusted blend door. This is a full flow blend system. The control valve has nothing to do with the heater, it's an AC component.

  6. #6
    Join Date
    Jun 2011
    Location
    Springfield, Ohio, USA
    Posts
    1,233
    My Cars
    1998 Z3 Roadster
    Poor heating performance at low RPM is usually caused by air in the cooling system. It must be bled properly, which means with the front of the car as high as possible and above 1000 RPM.
    Poor cooling performance at low RPM is usually caused by a bad Thermal Expansion Valve (TXV) or a bad compressor. The compressor is a variable-displacement type and sometimes loses its ability to change displacement.

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