No heat up front, but heat in rear on '83 'burb

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by FUNFINDER, Feb 9, 2009.


    FUNFINDER New Member


    First post, this board is great. I got an 83 C20 4x2 with the 454 for my birthday from the original owner. It's not a looker and needs a little TLC but overall runs like a champ. Truck was used to pull a horse trailer for its life and sat outside. Mechanically they took care of it, but i think I was the first person to vacuum the interior in several years. ;)

    The current mystery is the front heater. The blower works, but the heat never really gets hot. Oddly, if i switch to defroster the air coming out seems to be warmer, but its rarely, if ever hot. So i'm curious as to what might be causing it.

    Background: So far I've replaced the thermostat (thought maybe it was stuck open), temp gauge (broken) and rear heater core (leak made a mess out of cargo area), and redone the headliner (just proud).

    Info: when the rear heater was leaking, the coolant level was low, and so i figured that was probably it. now that that's fixed and the coolant level remains 'full' still the same problem. There's no (visible at least) coolant leak in the cab where the heater core is, but i haven't taken it apart to see as the coolant level stays good. The hoses going to from the heater core in the engine compartment are both hot. If i move the temp control from cold/hot, when its really cold out, it does get colder, so the damper seems to be working (at least some). And yes, I wait til the engine gets up to operating temperature (temp gauge pointing due north).

    All that being said, given enough time, the heater will heat up the truck, but it feels more like a heat pump (warmer enough to get the cab up in the 60's or 70's over enough time) but is never 'hot' (or warm even) if you stick your hand in front of it. By comparison, with the new core in the rear, when the truck is hot, if you turn the fan on, it blows hot air and the core gets VERY warm to the touch. (of course that motor had a short in it so i'm not using that til i can find a replacement, but i digress)

    Any ideas on what it might be and/or how to figure out what it might be?

  2. ct9a

    ct9a Epic Member 5+ Years 1000 Posts

    That's a stumper..... My best guess is that the damper door, while it may be moving, it may not be moving completely giving you only partial heat. Other than that, I have no clue what to do other than tear it down to the heater core and maybe replace it.
  3. JMoney02

    JMoney02 Epic Member 5+ Years 500 Posts

    If all components are getting hot, but air is not moving to the Hot side inside the Cab, I would also venture to say that the exchange doors are not fully operating correctly. How's the flow in the radiator? Go stream going by? Has the whole system ever been flushed?


    FUNFINDER New Member

    Exchange doors, eh? so... what/where can i find those? (I haven't taken apart the dash or engine side yet to look).

    A coolant flush, no. But when i replaced the heater core in the rear, i had to put in about 2.5 gallons of new coolant and when i did, to top it off, i saw that it was flowing around. I would say it was wooshing by the cap... but it was moving. I have no idea what rate it should move. I'm kinda new to this whole old truck thing... always been something i wanted to do, just never had the time til lately.
  5. GaryL

    GaryL Epic Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    If I'm not mistaken, the blend door is located in the box directly behing the glove box and is controlled by a cable. On my 78, the cable came off of the post on top of the box and so lost control of the door. Look in there and move the temp selector and see if you can find the cable and if it is still attached or not.
  6. JMoney02

    JMoney02 Epic Member 5+ Years 500 Posts

    Right On, GaryL. Its exactly where its located and some have the problem, some don't.....


    FUNFINDER New Member

    Thank you both. I'm at work and can't look, but i don't suppose its as easy to get to as just taking off the glove box door? or do i need to plan on taking off the entire dash?
  8. GaryL

    GaryL Epic Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    On my 78 I can empty out the glove box and bend the box a little and it will swing on down so I can reach the area you need to get at. No sure about the 83, but I would think the worst would be that you have to remove 4-6 screws for the door to get at it.

    FUNFINDER New Member

    Though I'd give a quick update on what I found. I finally got around to taking off the glove box. Boy was that easier than expected (4 screws). I then saw how the cable connects to the damper door of the duct system. Turns out there is a plastic stay on the cable that (i believe) is supposed to stay in place by this one screw. That broke off so the cable would just push and pull with the motion and would never fully open or close the damper door.

    My temporary fix was to zip tie the stay to the mount by running the zip tie through the screw hole. Not the sexiest fix, but it seems to have worked. I know for sure that the door/damper closes 100% because i can feel/hear it. Not 100% sure if it opens 100%, but i, for the first time ever, now get pretty hot air to blow out of both the heater and the defrost. just in time for summer. ;)

    The only bummer of it is that now all the way cold is about half an inch away from where the word cold is, but i suppose that's not that big a deal.

    Thanks to everyone for their help!
  10. vncj96

    vncj96 Epic Member 5+ Years 1000 Posts

    If the air temp is not hot then i would say a full POWER flush, even with coolant moving it can very easily plug things up, especially on an old vehicle like that, not to mention you have WAY more plumbing becasue of the rear unit. You can do it yourself with a kit and garden hose.

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