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Thread: 1990 Eldorado heater n/w

  1. #1
    vegasdano is offline Cadillac Owners Member
    Automobile(s): 1990 Eldorado
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    1990 Eldorado heater n/w

    My 1990 Eldorado heater is not working. There is no wetness nor smell, so I don't think it's the heater core. Is there a heater control valve, and if so, where is ti located. Thank you


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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1990 Eldorado heater n/w

    4.9? Has any work been done to the cooling system?

  4. #3
    vegasdano is offline Cadillac Owners Member
    Automobile(s): 1990 Eldorado
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    Re: 1990 Eldorado heater n/w

    The thermostat was replaced this summer

  5. #4
    VEGASELDO91 is offline Cadillac Owners Fanatic
    Automobile(s): 1991 ELDORADO (R.I.P.); 1995 Sedan Deville
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    Re: 1990 Eldorado heater n/w

    Not to thread jack but I noticed my heater isn't working either! I was told that the AC unit has been converted to R-134 and although it blows cold air the DIC says Refridgerant low/ AC compressor off. Don't know if this affected the heater or not.

  6. #5
    drewsdeville is offline Cadillac Owners Master
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    Re: 1990 Eldorado heater n/w

    You may have some problems behind the dash. Temp output is controlled by some linkage and doors behind the dash. Most of it is visible if you just take out the glove box...4-5 screws. When you switch from a warm to cool temp, you should see the linkage moving. If it's not moving, diagnose further.

    There is no real heater control valve on the '90, just a restrictor to the heater core on the heater hoses that can't "fail" besides leaking externally.

  7. #6
    SSG is offline Cadillac Owners Member
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    Re: 1990 Eldorado heater n/w

    Go into your on board diagnostics and check your coolant temperature. It should be over 195F or 85C. Just press the off and warmer buttons at the same time and hold them for about 5 seconds and you will go into diagnostic mode.

  8. #7
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1990 Eldorado heater n/w

    Sounds like an air mix actuator. Follow Drews advice.

  9. #8
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 1990 Eldorado heater n/w

    Check for code B440. The part is called the 'ECC Programmer'. Good luck finding a new one.... You can un-clip the bar that moves the air mix door and slide it manually to the heat position just to get you by until you can fix it.

    ECC is in green:

  10. #9
    vegasdano is offline Cadillac Owners Member
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    Re: 1990 Eldorado heater n/w

    Thank you for your responses, especially the photo. Will let you know what I find out.

  11. #10
    VEGASELDO91 is offline Cadillac Owners Fanatic
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    Re: 1990 Eldorado heater n/w

    I myself do not have the B 440 code but I do have the B 335 code in the history. Could this code affect the heating problem? It is becoming more than just a comfort problem now; my defroster isn't working and it is making it hard to see at times! Thanks!!

  12. #11
    VEGASELDO91 is offline Cadillac Owners Fanatic
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    Re: 1990 Eldorado heater n/w

    I pulled the glove box to check the linkage arm (just to be sure); it seems to be working properly. Where should I look to next? Thanks!

  13. #12
    drewsdeville is offline Cadillac Owners Master
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    Re: 1990 Eldorado heater n/w

    The since the code is in history, and you verified the Climate Control is working correctly, I woudn't worry about the B335. What's th engine temp in the DIC when you are trying to use the heat?

    If the temp is normal operating temp, I'd have to suggest the heater core is plugged or disconnected. That or you have air in the system due to combustion leakage through headgaskets... Do you ever have to add coolant?

  14. #13
    VEGASELDO91 is offline Cadillac Owners Fanatic
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    Re: 1990 Eldorado heater n/w

    Quote Originally Posted by drewsdeville View Post
    The since the code is in history, and you verified the Climate Control is working correctly, I woudn't worry about the B335. What's th engine temp in the DIC when you are trying to use the heat?

    If the temp is normal operating temp, I'd have to suggest the heater core is plugged or disconnected. That or you have air in the system due to combustion leakage through headgaskets... Do you ever have to add coolant?

    Thank you for the tips and info.; I found the problem! It turns out one of the hoses that connects to the heater core was totally disconnected and the other was rerouted and connected to the T connecter. I had to face the possibility that the heater core was leaking and the previous owner disconnected it. I reattached the hoses to their rightful places (thanks to ALL-DATA) and started the car; there was a little seepage from one of the hoses and as the car got hotter it started to actually spray! There was no fluid leaking into the cabin and it felt like it was starting to warm up!!

    I cut the hose past the area that was leaking and reattached it, I let the car run for around 20 min. with temp set at 90 and on high. It took awhile for it to heat up the cabin but there was no leaks noted, as I drove around the parking lot of my job it started to get hotter faster. So hopefully the only problem was the leaking hose (already ordered new ones), I will drive it home and let it sit overnight and check for moisture in the passenger side tomorrow.
    Thank you again for your helpful info; and I hope Vegasdano finds his problem too!

    P.S. Sorry for the novel post!!

  15. #14
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 1990 Eldorado heater n/w

    The ONLY reason to bypass the heater core is because it has a leak. If it is small, it may not drip, but it will fog the windows so keep an eye out for that.

  16. #15
    VEGASELDO91 is offline Cadillac Owners Fanatic
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    Re: 1990 Eldorado heater n/w

    Quote Originally Posted by Ranger View Post
    The ONLY reason to bypass the heater core is because it has a leak. If it is small, it may not drip, but it will fog the windows so keep an eye out for that.
    I will definately keep an eye out; thank you for the tip! Just so I understand; will it only fog up the windows when I am using the heater or will it still do it when the heater is off too?

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