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  1. #1
    Join Date
    Oct 2009
    Location
    Beloit, WI
    Posts
    77

    Default Help! No heat, ambient temp display reads --

    The temp display on our has been wonky for about a year now, in the past it has read a temperature that may or may not have been correct, or typically it has read "--". The HVAC system will run the A/C or heat when it feels like it. With winter coming up and the wife needing heat, I replaced the temp sensor in the mirror with a new Volvo part from FCP, based on information I read on this and other forums. After the replacement, the display reads "--", and will not show a temperature. Figuring I received a defective part, I ordered a new one and replaced it this evening. No dice. It still reads "--" and I have no heat. This week is the coldest of the year so far and I'm looking for options. I've flushed the heater core and it flows fine, and it has newer coolant at the appropriate level. I'm convinced it's electrical, but I don't know where to go from here.

    Any help would be GREATLY appreciated!
    The current fleet:
    2006 Volvo XC90 T5
    1992 Audi S4
    2007 525xi
    1988 VW Scirocco 16v (autocrosser)

  2. #2
    Join Date
    Dec 2009
    Location
    GA
    Posts
    1,420

    Default

    Quote Originally Posted by bronson75 View Post
    I replaced the temp sensor in the mirror
    which mirror? there is one in each outside mirror, with different functions.

  3. #3
    Join Date
    Oct 2009
    Location
    Beloit, WI
    Posts
    77

    Default

    Quote Originally Posted by hoonk View Post
    which mirror? there is one in each outside mirror, with different functions.
    From what I've read, there is only one sensor, located in the driver's side mirror. I drove it to work the day after I replaced the sensor, and it showed the "--" for the first few minutes, then it showed an accurate temperature for the rest of the 30 minute drive (8*-10* F), but still no heat. The drive home and ever since, it showed "--". I think the sensor is okay, but it's getting an intermittent signal or there's some other electrical problem. I don't have a Volvo specialist or dealer close to me too yet it diagnosed, I'll take it to my regular mechanic to see if he can help, but I'm stumped at this point.
    The current fleet:
    2006 Volvo XC90 T5
    1992 Audi S4
    2007 525xi
    1988 VW Scirocco 16v (autocrosser)

  4. #4
    Join Date
    Dec 2009
    Location
    GA
    Posts
    1,420

    Default

    Note item 6 in Vida Parts catalog, left and right temp sensors

    Click image for larger version. 

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  5. #5
    Join Date
    Oct 2009
    Location
    Beloit, WI
    Posts
    77

    Default

    Quote Originally Posted by hoonk View Post
    Note item 6 in Vida Parts catalog, left and right temp sensors

    Click image for larger version. 

Name:	mirror temp sensor.jpg 
Views:	9 
Size:	70.5 KB 
ID:	8458
    While I haven't taken the passenger side mirror off yet, I'm referencing this thread:
    http://forums.swedespeed.com/showthread.php?t=228586

    I'm pull the passenger mirror tomorrow to confirm.
    The current fleet:
    2006 Volvo XC90 T5
    1992 Audi S4
    2007 525xi
    1988 VW Scirocco 16v (autocrosser)

  6. #6
    Join Date
    Oct 2009
    Location
    Beloit, WI
    Posts
    77

    Default

    Update: I'll concede being less than knowledgeable. I popped off the cover on the underside of the passenger side mirror, and lo and behold, there is a sensor in there. Something I should have checked before, I suppose.
    The current fleet:
    2006 Volvo XC90 T5
    1992 Audi S4
    2007 525xi
    1988 VW Scirocco 16v (autocrosser)

  7. #7
    Join Date
    Oct 2009
    Location
    Beloit, WI
    Posts
    77

    Default

    Update #2: I swapped out the passenger side mirror sensor (temporarily) with the drivers side sensor I thought was bad. I'm getting a reliable accurate outside temp on the display now. I let the car heat up (it's -3* here now), and used my infrared thermometer and touch to check various heat points: upper radiator hose, heater core inlet and outlet at the firewall under the hood, and heater core inlet and outlet at the heater core under the dash. The engine warms up quickly (confirmed by the engine coolant temperature gauge and a hot upper radiator hose). The heater core hoses show the same result. Plenty of heat getting into the heater core, and the outlet is cooler than the input, which shows it is losing heat like it should be. But the end result is the same, no heat on any setting, auto or manual mode. I have a friend who works at a local garage who has access to Volvo diagnostic software, I'll get it to him this week and see if he can diagnose the issue. I also blew out the interior temp sensor fan on the center console with a can of compressed air.
    The current fleet:
    2006 Volvo XC90 T5
    1992 Audi S4
    2007 525xi
    1988 VW Scirocco 16v (autocrosser)

  8. #8
    Join Date
    Dec 2009
    Location
    GA
    Posts
    1,420

    Default

    Quote Originally Posted by bronson75 View Post
    The HVAC system will run the A/C or heat when it feels like it.
    Could possibly be an evaporator temp sensor - check the readings with VIDA (or a capable scan tool) to make sure

  9. #9
    Join Date
    Oct 2009
    Location
    Beloit, WI
    Posts
    77

    Default

    So I did a bunch of poking, prodding and checking today. I checked the function of the blend doors, thinking they were bound up, had bad actuators, broken arms, or needed to be calibrated. Everything worked as expected, when I turned the temp knobs from cold to hot, the arms moved the doors fine, on both driver and passenger side. I checked the temperature of the air flow coming out of the foot vent while changing the temp on the dash, and there was only a few degree difference between hot and cold. The metal inlet and outlet tubes at the heater core were hot to the touch (I couldn't get a good reading with my infrared thermometer), but the core itself was ice cold. I have a feeling it may be an original part, I know for certain it's an OEM part, and after 180,000 miles I'm sure it's plugged up almost solid. I did a heater core flush a year ago and got what I thought was good flow, but it must not have been flowing the whole thing. I have a core ordered, and I'll update this thread with my findings.
    The current fleet:
    2006 Volvo XC90 T5
    1992 Audi S4
    2007 525xi
    1988 VW Scirocco 16v (autocrosser)

  10. #10
    Join Date
    Oct 2009
    Location
    Beloit, WI
    Posts
    77

    Default

    Quick update:
    After verifying that all the flap doors were moving correctly, I ordered and replaced the heater core (the last link in the chain). We now have heat to spare!
    The current fleet:
    2006 Volvo XC90 T5
    1992 Audi S4
    2007 525xi
    1988 VW Scirocco 16v (autocrosser)

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