MK2 Heater core replacement! w/AC! & Heater core bypass! - FAQ/Tech Tips/Please Read First - VWDiesel.net The IDI, TDI, and mTDI source.

• MK2 Heater core replacement! w/AC! & Heater core bypass! by jtanguay on 14 Jul, 2009 16:27
• Well I finally got around to posting how its done.  If anyone has suggestions feel free to add to this post, but please only relevant info to keep it clutter free.  Thanks
  
  First off, both lower access 'panels' must be removed.  On the passenger side there is a strap holding everything together.  This has to be cut.  Next the glovebox has to be removed.  Now the center console must be removed.  The radio and other bits have to come out as well to make it easier to unhook certain ducts and replace the foam. Once you remove the duct for the two center vents, it should look something like this:
  
  
  As you can tell from the picture, the foam has all rotted due to age and coolant spray.  I also discovered why I get air out of all vents regardless of selector position; the gear on the vacuum controller broke under stress from some sticky residue.  A little glue and its all better.
  
  At this point you should disconnect the A/C lines.  I suggest using a short stubby wrench as it is very tight in this area.
  
  
  Now, if you have turbo you need to remove the heat shield to access these two nuts on the firewall.  
  
  
  Going back into the car, there is a bolt up under where the glovebox was.  In the picture below It's removed.
  
  
  Now it takes time, patience, and a lot of wiggling to get the whole unit out.  After a big struggle, I was able to get it out.  Notice the clean floor mat    To separate the heater box, there are little metal clips.  The plastic clips can be wiggled free, or broken. Tape could be used on the joint to seal it up.
  
  
  Time for some cleanup, etc.
  
  Now for some new foam!
  
  
  Here's the new heater core installed.  Make sure to put the adhesive foam that comes with it on as the fins will catch and get bent on installation without it, and it just makes a good seal!
  
  
  And installation is reverse!  
  
  Another issue is that the heater core always has hot coolant running through it.  If you didn't want to take the time to replace the foam on the different flaps, you could always run a bypass system.  This would give nice cool air on an old beater during the summer, and even cooler a/c as well.  I'm definitely installing this mod!  The two main components that you need can be purchased from rockauto (that links you to a cart already filled with the two main components)
  
  The vacuum solenoid:1990 CHEVROLET ASTRO 2.5L 2474cc 151cid L4 TBI (E)
  Emission : EGR Vacuum Solenoid AIRTEX Part # 2F1120
  (EGE Valve Vacuum Bleed Valve Solenoid)
  
  
  And the bypass valve:Heat & Air Conditioning : Heater Control Valve
  FOUR SEASONS Part # 74809  
  
  
  
  The rest of the hookup is pretty easy.  All you need is a vacuum tee going from the solenoid to the bypass valve with vacuum from the engine, and a solenoid switch on the dash somewhere to activate flow when you want it.  Also, some 3/4" cooling hose might be needed, and some clamps as well.  Be sure to have the system hooked up so that hot coolant is only flowing when vacuum is applied to the bypass valve.  Now might freeze, but you won't have to pull over for another blown heater core
• #1 by fdnyguy on 15 Jul, 2009 18:25
• I coulda used this $700 ago...  
  
  
  Stay safe, stay well. Jimmy.
• #2 by jtanguay on 16 Jul, 2009 14:14
•    there might also be a way of just removing the heater box for some of you guru's out there...  maybe theres just enough room with the help of a mirror to get the rear metal clips?  but anyways, i hope this helps people out!
• #3 by dieselherb1 on 01 Aug, 2009 10:46
• I have pulled a A/C-Heater unit out of a 81 pickup. Wasn't too bad only 2 nuts holing it to the firewall-dash that I remember. Is the MK2 that much different? If so then sounds like main work installing into a MK1?
  Herb
• #4 by truckoSaurus08 on 11 Aug, 2009 19:51
• I just tore the whole dash out. wish i would have known about this little trick sooner. That strap must be the giant zip tie thing on the evaporator box. Right?
  I remember having trouble with those dang speed nuts.
• #5 by jtanguay on 06 Sep, 2009 21:59
• Quote from: truckoSaurus08 on 11 Aug, 2009 19:51

  I just tore the whole dash out. wish i would have known about this little trick sooner. That strap must be the giant zip tie thing on the evaporator box. Right?
  I remember having trouble with those dang speed nuts.
  

  
  yea the strap is pretty big
  
  i forgot to give caveman props for giving me tips on how to git r done i probably would have cried if the whole dash had to come out, although its not as bad as it seems (its worse! lol)
  
  that heater core bypass is my new best fwend.  no more heat bleed into my cool a/c and it just puts less stress on the heater core when the heater core really doesn't need to be used... for the win!!!
• #6 by VW_Commuter on 20 Aug, 2010 23:29
• FYI, I just received my vacuum solenoid described in this FAQ by jtanguay and it requires a special electrical plug.  I found one on Amazon but it probably can be found from many different sources.  Here is the link, http://www.amazon.com/gp/product/B001RPYVT8/ref=oss_product, for the one I purchased (it was the cheapest I could find and was a complete pigtail assembly).
• #7 by honda_is_the_best on 21 Aug, 2010 13:06
• is the MK2 dash harder to pull than an mk3? because i didnt find a mk3 dash all that hard to pull.
  
  now, if you guys want a challenge, change the heater core on a mid 80s toyota pickup.. you end up with a bed full of dash pieces when you get to the actual heater core. it takes literally like 6 hours, iirc..
• #8 by JBG3 on 02 Nov, 2012 10:38
• thanks for this thread!
  
  I went the other route and pulled the whole dash out, but I had additional issues to resolve as well.
  
  I was going to mention that instead of foam, what also works great if you have some, is stair treading on both sides-
  
  
  
  Added benefit for me was that the treading had a safety stripe, so I now have a racing stripe inside my climate control.
  
  Also, I had an additional problem in that my cable control had moved underneath, if you flip the control vent box upside down, there is a zip tie controlling the cable connection location for the door movement.  On mine it had moved, and the door would not fully redirect, ending with about a 1.5 inch gap either way.  I cut the zip tie, and moved where it grabbed the cable sheathing, so that at either end of the control level, the door actually redirected fully.
  
  
• #9 by damac on 18 Aug, 2017 12:25
• anybody have results for this setup long term?  found by accident searching google and never thought of such a thing.  i have a couple golfs i am fixing to get rid of so i think i will leave those stock.  ac is doing pretty good.
  
  but for my own car if i can give the ac any help on those 100 degree days it seems like a no brainer.