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  • Heater only blows luke warm air

    The heater is my 99 nbs won't blow really hot air like my smaller ranger. What do I need to look at or have serviced? I read somewhere that a clogged cabin air filter could cause this but haven't checked that yet because it's been frigging cold outside and I've been driving my Ranger.
    1999 Silverado LS 4x4 Z71 w/ 5.3L

  • #2
    Re: Heater only blows luke warm air

    Is the truck warming up to normal motor temp? Coolant full? heater core and air box full of dirt? Blend door moving all the way?

    Thats where I would start
    04 ECSB 5.3 4x4 Z71
    06 Front clip, Reflexion steel hood, Escalade touch screen nav, Escalade wood steering wheel
    06 E Fans and Rad, 2 Alpine subs, 250 amp MechMan alternator, Dual battery with isolator
    05+ front brake swap, Suburban rear brake swap,Rusty door bottoms,Line X,PCM4Less tune

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    • #3
      Re: Heater only blows luke warm air

      Thanks for the starting points.

      The truck warms up normal. Coolant is full. I will check the air box and heater core. What's the blend door?
      1999 Silverado LS 4x4 Z71 w/ 5.3L

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      • #4
        Re: Heater only blows luke warm air

        My son had this problem on his 02 Z71. He removed the hoses from the heater core and blew it out with air and then a water hose. Heater core was restricted. Works great now.
        2004 2500 ccsb 6.0, Superchips, 265/75/16 Toyo A/T's.

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        • #5
          Re: Heater only blows luke warm air

          This is the time of year when this sort of thing becomes very common. NBS trucks typically suffer from either clogged cabin air filters or a clogged heater core, or maybe both at the same time. The heater core back flush is very easy to do, and if that doesn't resolve things, go after the cabin air filters.
          00 RCSB Z71/JBA cat-back/Z71 Tahoe valance/EBC slotted&drilled rotors with SS lines & SS braided hoses/Edelbrock headers/BB tune/6000k HID low beam & fog lamps/Auto-headlight disable mod(nice)/Vette servo/LT1 E-fans/LED gauge cluster/Titan 18" wheels/Rollpan/Belltech rear sway bar/2-4 drop

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          • #6
            Re: Heater only blows luke warm air

            Well I just changed the cabin air filters and you were right, they were FILTHY! I doubt they have ever been changed and truck is 11 years old with 200k miles. I'll let you know if that fixes the heating issue. I'm hoping it does since they were so nasty.
            1999 Silverado LS 4x4 Z71 w/ 5.3L

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            • #7
              Re: Heater only blows luke warm air

              No heat usually means a clogged heater core if everything else is fine. Warm, but not hot air, is usually a pair of clogged cabin filters. I bet replacing your filters has made a big difference.
              00 RCSB Z71/JBA cat-back/Z71 Tahoe valance/EBC slotted&drilled rotors with SS lines & SS braided hoses/Edelbrock headers/BB tune/6000k HID low beam & fog lamps/Auto-headlight disable mod(nice)/Vette servo/LT1 E-fans/LED gauge cluster/Titan 18" wheels/Rollpan/Belltech rear sway bar/2-4 drop

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              • #8
                Re: Heater only blows luke warm air

                The heater core probably needs to be bled. If the core is full of fluid and there is air in the feed side (WP Out) hose the air will act like a spring. The air will compress, but the WP doesn't have enough "Umph" to push the air bubble combined with the weight of the fluid inside the core w/out winding the pi$$ out of the motor. I take the hoses off the core and blow the fluid out of the core using compressed air. Be careful, the fluid will spray all over the engine if you don't do something with the other tube. I usually use a large towel. Reconnect the hoses, add fluid and run the engine.

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                • #9
                  Re: Heater only blows luke warm air

                  I would try a blend door reset ! Its easy and free:

                  It is most likely the Blend door actuator.

                  BUT before you go to the dealer try the reset procedure thats
                  been floating around on the GM forums:

                  Try looking for the HVAC fuse under the hood.
                  pull the fuse for about five minutes, reinstall it then turn the ignition on don't touch the controls for another 5 minutes. The system will run through all the settings.

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                  • #10
                    Re: Heater only blows luke warm air

                    Does this reset work on the pre 99 trucks (OBS)
                    V INTIMIDATOR has been SOLD V

                    98 RCLB Z71 all stock

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                    • #11
                      Re: Heater only blows luke warm air

                      i would try blowing air through it first. just disconnect both of the hoses and blow air through one side of it. i had this problem and this fixed mine, it was just clogged up.

                      1993 GMC SIERRA with 1996 corvette lt1. Built 4l60e. 4.10 gears. Eaton positrac. Dual exhaust. 1996 dash swap. 2002 electric tahoe seats. More to come

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                      • #12
                        Re: Heater only blows luke warm air

                        It made a pretty good difference in the amount of heat that it puts out now. It's not super hot like in some trucks, but it's warm enough now that I get uncomfortable if I wear anything besides a shirt when the heat is on.
                        1999 Silverado LS 4x4 Z71 w/ 5.3L

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                        • #13
                          Re: Heater only blows luke warm air

                          take the two hoses going to the heater core and swap them for a couple days prob the dex cool (evil satan juice) pluging up in the core if so this works every time :)

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                          • #14
                            Re: Heater only blows luke warm air

                            You just might need a new thermostat.

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                            • #15
                              Re: Heater only blows luke warm air

                              which FSC's came with a cabin filter?

                              Used to own a FSC, now I just have my extremely old Buick.
                              Have some perspective please. Thank you.

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