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  1. #1

    Default Front heat blowing cold on 2000 Yukon

    I have a 2000 Yukon and the problem I am having is no heat coming out of the front vents, just cool air. The rear blows hot like normal but the front is barely luke warm. I checked the blend door actuator right above the transmission hump and it works fine. I guess now I will try flushing the heater core but needed some advice before trying. How hard is it to disconnect the heater hoses from the heater core? Does it take a special tool? Which side is the inlet and which is the outlet? What is the best thing to use for flushing it? Any help on this will be greatly appreciated!

  2. #2

    Default

    If you are sure the temp actuator is working fine, the problem is probably (as you suggest) coolant related. You should be able to find the hoses going to the HVAC unit. They would connect to fittings on the firewall. If the hoses are not hot, the suspicion of a coolant problem is confirmed.
    I have had this problem, on previous trucks, it is usually just a low level of coolant. Top it up and things are fine.
    If the level is good, perhaps something is plugging a hose, or a hose has collapsed.
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  3. #3
    Jr. Engineer Jamm3r's Avatar
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    Though rare it is possible that the damper has come unstuck from the actuator lever, especially if the truck has been in a collision. You may be able to look inside the duct with a flashlight and mirror to observe whether the blend door itself actually moves. I had this problem once with the heater/defroster blend door and was able with some fiddling to hook it back on without disassembling or removing the duct assembly (which is a huge job).

    The heater hoses connect to the core with a bog standard hose clamp.
    Minneapolis area - 1997 K2500 regular cab long bed + 8.5' Western Unimount plow + modified transmission + 2nd battery + modified camper charge circuit + 1971 Cayo camper -and- 2004 4x4 Suburban 2500 8.1 + Maxbrake controller + 2nd battery + modified trailer charge circuit + Reese receiver, pulls 30' Airstream trailer

  4. #4

    Default

    Thanks for the replies. The coolant level is good and not low, even added some about a month ago and no change. When I took the actuator loose I was able to move the blend door manually and still is was blowing cool. At one point I turned the blower fan off for a couple of minutes and turned it back on and it would blow hot for about 15 - 20 seconds and then back to cool. I was going to try to disconnect the hoses at the heater core itself but the clamps look like they need a special tool.

  5. #5

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    Quote Originally Posted by Maxx1500 View Post
    When I took the actuator loose I was able to move the blend door manually and still is was blowing cool. At one point I turned the blower fan off for a couple of minutes and turned it back on and it would blow hot for about 15 - 20 seconds and then back to cool. .
    Sounds like you have hot coolant in the HVAC unit and you have blend door/actuator problems, but still not sure.

    Quote Originally Posted by Maxx1500 View Post
    I was going to try to disconnect the hoses at the heater core itself but the clamps look like they need a special tool.
    Are they hot, is the hot coolant flowing through the hoses. If they are hot, there is no need to disconnect them.

  6. #6

    Default

    The blend door actuators are known to go bad. I vote for that. Also, try disconnecting the battery for 15 minutes. Reconnect it, turn the key forward and turn on the hvac control. Do not touch it after it is turned on, wait about 90 seconds and then start the truck. This will recalibrate the actuators. I had the same issue at one time with my truck. I did the above and it has been fine since.

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors, http://www.gmtruckclub.com/forum/sho...5-GMC-Yukon-XL
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

  7. #7

    Default

    ^^ good advice @Pikey, I've had that work for me as well.

  8. #8

    Default

    Well I tried resetting the actuators as recommended and still ended up with the same results. After a long test drive I touched the tubes from the heater core and the left was hot but the right side was cool. Took hoses loose and inserted a blow gun connected to the air compressor into the right tube. Connected a loose hose to the inlet side and proceeded to blow out the heater core. A lot of gunk and chunks of dried up dexcool came out. Then I mixed some CLR with water and injected it into the heater core and let it sit for 2 minutes. Flushed it out using the garden hose for about 2-3 minutes then put it all back together. Refilled the water and anti-freeze and let it run for a while and now the heat blows hot like it should.

  9. #9

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    Dear At one point I turned the blower fan off for a couple of minutes and turned it back on and it would blow hot for about 15 - 20 seconds and then back to cool...!!!
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  10. #10

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    Quote Originally Posted by Maxx1500 View Post
    Well I tried resetting the actuators as recommended and still ended up with the same results. After a long test drive I touched the tubes from the heater core and the left was hot but the right side was cool. Took hoses loose and inserted a blow gun connected to the air compressor into the right tube. Connected a loose hose to the inlet side and proceeded to blow out the heater core. A lot of gunk and chunks of dried up dexcool came out. Then I mixed some CLR with water and injected it into the heater core and let it sit for 2 minutes. Flushed it out using the garden hose for about 2-3 minutes then put it all back together. Refilled the water and anti-freeze and let it run for a while and now the heat blows hot like it should.
    Glad your caught that before the entire heater core was plugged. Not a fun job to replace.

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