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Thread: Defroster issues

  1. #1
    Join Date
    Oct 2001
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    Granby, Missouri, USA
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    Question Defroster issues

    1995 K1500 Tahoe 6.5L diesel

    I have been experiencing issues with my defroster this winter. Turning on the defrost actually causes all the windows and windshield to get fogged up. I dread having to use the defrost setting since I know it will make everything worse before it gets better. After about 10 minutes of driving, it finally clears everything up, but I have to leave it on high the entire time for it to work.

    I am noticing a musty smell from the vents as well. There must be excess moisture in the HVAC system.

    Here's what I've checked:

    A/C Compressor is running
    Air is coming out of defrost vents normally
    I removed the blower motor to check the evaporator, and it is clean
    Evaporator drain is open and flowing normally

    What do I need to check next? I suspect an issue with the heater core, but I don't appear to be losing any coolant. Haven't had to add any coolant in months.

    Thanks,

    Casey
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  2. #2
    Join Date
    Apr 2001
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    Default

    Make sure your recirc isn't stuck. Defog mode should force fresh air and disable recirc. If it's stuck, or not cycling properly, it's condensing all the moisture in the cabin onto the glass, until it warms up enough to vaporize it, and condense it again in the evaporator. Other than that, it's likely the heater core. It doesn't take much leakage to fog the glass. A few drops at a time is all it takes, and you may not notice the missing coolant.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  3. #3
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    Default

    Quote Originally Posted by DmaxMaverick View Post
    Make sure your recirc isn't stuck. Defog mode should force fresh air and disable recirc. If it's stuck, or not cycling properly, it's condensing all the moisture in the cabin onto the glass, until it warms up enough to vaporize it, and condense it again in the evaporator. Other than that, it's likely the heater core. It doesn't take much leakage to fog the glass. A few drops at a time is all it takes, and you may not notice the missing coolant.
    DOH! I didn't think of that! The recirc door has been broken (or rather the actuator) for some time, and I've actually wired it closed into the recirculate position for better summer time A/C performance. I will try that first.

    Thank you sir!

    Casey
    Last edited by arveetek; 01-23-2020 at 09:18.
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  4. #4
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    Yep. That'll do it.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  5. #5
    Join Date
    Mar 2000
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    South Central Pennsylvania, USA
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    Yep, that would do it. Hopefully it isn't the leaking heater core (my first thought) as that's a royal pain to replace.
    '94 GMC 6.5TD K1500 4L80E 2-Door Yukon SLE 221K
    '93 Chevrolet 6.5TD K2500HD NV4500 Std. Cab Longbed 187K
    '85 Toyota 22R RN60 4x4 Std. Cab Shortbed 178K (Currently retired for rebuild)
    Diesel Page Member #2423

  6. #6
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    Default

    I've only driven it 3 or 4 times since moving the recirc door, but crossing my fingers... so far so good.

    Casey
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

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