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    Thread: DIY: MK IV Heater Core Replacement

    1. Member AZV6's Avatar
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      11-23-2009 10:22 AM #36
      Just did this last night, took me about 3 hours. Pretty simple.

    2. Member AZV6's Avatar
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      11-25-2009 06:06 PM #37
      Be aware that all heater cores out there are not the quality of OEM. Valeo (made in Mexico) and others that cost anywhere from $39-55 are garbage.

      Stick with OEM on this one. It is a valeo made in France. Mine lasted 166K miles.

      After all the work, don't bother with the cheapy ones!


    3. Member darisd's Avatar
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      12-04-2009 07:00 PM #38
      Quote, originally posted by grantndub »

      Yep there must be two different ones. Mine had no clips at all. My GTI is a 2000 maybe even a late 99. So I would expect later models to have the clips and box would nbe able to split. I had to pull the hole box out and recharge my a/c later. Lucky for me I was able to recharge it at my work.

      Updated. I added a step 15b and another reassembly step. Thanks to you and Afghandelight for tracking this down!


    4. Member
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      12-07-2009 09:27 PM #39
      Thanks for this in advance, my wife's jetta has been losing coolant(a string of issues since her waterpump blew and she burned out the headgasket... I've had a bunch of busy weekends and feared I'd have to redo the head), had "water" in the passenger rear footwell as it has in the past after big rainstorms so figured it was the same. Attributed the foggy windows to that (ok, smelled coolant, didn't connect it before) and didn't think much of it till the core blew on the drive home tonight and I saw the puddle on the front passenger floor. Realized pretty quickly then what it was.

      New core is on the way, looped off the lines in the engine bay for now and will be driving with gloves and a coat on. Of course she wants a new car and to trade this in for the 50 bucks they'd offer... Gotta fix it fast


    5. Member darisd's Avatar
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      12-09-2009 03:28 PM #40
      Quote, originally posted by slugman »
      Gotta fix it fast

      The great part about this job is you get to escape to the garage for a weekend. Cleaning the carpets will be a pain in the arse though.


    6. Member B. Elliott Karnes's Avatar
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      12-09-2009 04:53 PM #41
      Quote, originally posted by darisd »

      The great part about this job is you get to escape to the garage for a weekend. Cleaning the carpets will be a pain in the arse though.

      this job blows

      Facebook friends?

      Lexus of Knoxville - Knoxville, Tn

    7. 12-09-2009 07:04 PM #42
      No problem haha..turns out its either impossible or super not recommended that you depressurize your a/c yourself...i wish i couldve just had the clips

      great write up though, got through all the correct steps with no problems..


    8. 12-10-2009 06:16 PM #43
      Quote, originally posted by lespaulman16 »

      this job blows

      Yep, there's no nicer way to say it


    9. 12-10-2009 08:58 PM #44
      difference between the split and non split cases is whether you have a climatronic system or not

      i happen to have climatronic lol


    10. Member darisd's Avatar
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      12-12-2009 05:26 PM #45
      Quote, originally posted by Afgandelight »
      difference between the split and non split cases is whether you have a climatronic system or not

      i happen to have climatronic lol

      Of course... gah that did not occur to me.

      Off to change the writeup again!


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      03-26-2010 08:39 AM #46
      Starting this project in about 2 hours Dear lord, what the hell am I getting into?

      Did it and I am SO completly happy with the results EVERYTHING, and I mean EVERYTHING works as if it was never taken apart, no left over pieces, NOTHING Wasn't hard, just alot of stuff to remove. The only thing that us some trouble was popping off the air bag and trying to hit those releases.


      Modified by Quattro Krant at 5:41 AM 3-28-2010


    12. 04-23-2010 08:15 PM #47
      Anyone know what the inner diameter is on the heat core hoses?

      I'm stuck at school with limited tools, so won't be able to get around to permanently fixing the heater core until another couple weeks. In the meantime, I'm going to have to bypass it... and would rather buy the misc. hardware to bypass before I start, then have to go out after I start.


    13. 07-11-2010 02:46 PM #48
      In the middle of this job now on my girlfriend's 2000 Golf and found a few things...

      1. No need to remove the steering column bolt under the cowl.
      2. I didn't touch anything rearward of the shifter console.

      3. And the big, bad one... this car is NOT equipped with Climatronic, and the case is one piece!

      I now have the car torn apart and have to discharge the AC in order to continue. How can I do this, and what damage will I do by not having it properly evacuated?

      BTW... thanks to those who put together these nice writeups. Well done!

    14. Member silvr rcr's Avatar
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      07-11-2010 09:18 PM #49
      i had the same problem, my car doesnt have climatronic either.
      we were going to just roll it out of the garage and loosen one of the a/c lines to discharge the r134 or whatever it is, but there was ice on the incline driveway, so we'd have never gotten it back in.
      i ended up putting everything back together and it was 3 months before i got back around to pulling everything apart again, used the heat ONE TIME before warm weather came again, haha.
      i cant say its not safe to just discharge your a/c system without the machine, but do what you gotta do (either that or put it back together to drive it to a shop)

    15. 07-12-2010 11:16 AM #50
      Quote Originally Posted by silvr rcr View Post
      i cant say its not safe to just discharge your a/c system without the machine, but do what you gotta do (either that or put it back together to drive it to a shop)
      I talked to my girlfriend's mechanic brother. He said no harm will be done to the car, but I did burn a tiny little hole in the ozone layer.

      I vented it slowly at the expansion valve and got what had to be done taken care of. I'm going to have the cooling system flushed today, and then recharge the AC. I'm currently in the middle of trying to use all the little screws I took out while putting this puzzle back together.

      Definitely cant say I'm bored!

      OP... you may want to edit the Climatronic = one piece case vs. cable acuated = two piece case. It apparently isn't that easy. Thanks again!

    16. 11-23-2010 01:27 AM #51
      thank you so much for posting this!!!! people just started talking about snow and my heater was blowing coolant fumes.... $50 and a blood sacrific was all it took to fix this lol (aaaaaaand about 48 hours....but hey) thanks again

    17. Member lite1979's Avatar
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      12-02-2010 02:11 AM #52
      That's one heck of a nice write up. I don't know if I'll have time to do this this winter, but I have heated seats, so I may just bypass the heater core until the spring and do this then. I'm driving a 2001 Audi TT, but hopefully there's not too much different about the setups..

    18. Semi-n00b
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      01-22-2011 03:39 AM #53
      I just wanted to thank you for this writeup and your dashboard removal writeup. i could not have dont the heater core replacement without them.

    19. Junior Member
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      02-08-2011 10:44 PM #54
      darisd - great writeup!

      spent the weekend doing this, no major problems. had to replace the quick release fittings going to the core though - o-rings were shot, once i cleaned off the dried coolant, they leaked like crazy.

      i was long overdue for a new core!


    20. Junior Member jmaynard7's Avatar
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      03-25-2011 08:59 PM #55
      Ok, I've followed the instructions to a T. Found 2 nuts on the firewall under the heat barrier in the engine compartment that needed to come out. I've separated the A/C lines, etc. Still, there is something not allowing me to pull out the box on the left side. I've looked and looked and still cant find what I'm missing. Ive got a ton on experience in auto repair. I've replaced engines, transmissions, etc, and never had this much trouble finding what is going on. This is a 2003 Jetta, 2.0L, NON-Climatic, without clips.

      Any help would be appreciated. And BTW, AWESOME write up! I'll be adding some things to it from this model, and in a month or two will be creating some DIY's for this car, my 1994 Passat VR6, and my 2000 A6 Avant.

      Thanks in advance!!

    21. Junior Member
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      03-25-2011 10:22 PM #56
      There's two more studs coming thru the firewall on the passenger side. I could only find them by feeling thru the fiber mat on the firewall. There's an AC expansion valve on the firewall, I think one stud was above it and one just below it. Took me a while to find them, just keep feeling around for them.

    22. Junior Member jmaynard7's Avatar
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      03-26-2011 03:18 AM #57
      Quote Originally Posted by katc View Post
      There's two more studs coming thru the firewall on the passenger side. I could only find them by feeling thru the fiber mat on the firewall. There's an AC expansion valve on the firewall, I think one stud was above it and one just below it. Took me a while to find them, just keep feeling around for them.
      Thank you SOOOOO much! That was exactly what I was missing! After I removed those it came right out!! I searched and searched and never thought they would be that hidden. The other two that were behind the heat shielding in the engine compartment at least had pop outs that were visible. At least reassembly wont be near as bad I'll attach a pic of their locations tomorrow so the next guy wont be as aggravated. Thanks again for the quick response. Man I love this forum!

    23. Junior Member
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      05-17-2011 12:04 AM #58
      Howdy All -
      Thought I'd post some pics of this job for us suckers who have NO SPLIT and NO CLIMATRONIC. 2001 Jetta 2.0. Cable Controls. Much swearing when I finally got the dash off and realized I have no split:



      After safely having the system discharged, the guide still works, but had to completely remove pass side bolt on center crossmember, have helper hold up crossmember, and wiggle hvac box down and sort of into pass footwell to get it up and out of the car.

      I was following the guide to get to my nasty degraded foam on the mixer doors. Got the box out of the car and couldn't for the life of me figure out how to open it (it didn't help that I was on my 3rd beer to get over the frustration of no split.) There's a screw deep down in the recess right next to the slot for the heater core:


      OK - got the box open - finally get to see the REALLY GROSS FOAM ON THE FLAPS:


      If you're going to go through all the effort to get to the HVAC box, might as well clean what's left of the nasty foam off and seal the holes in the doors with something. I'm going with metal duct tape and some weatherstripping. Here's hoping it lasts/dosen't whistle or anything:


      Lastly - for those folks who are having trouble finding the studs that go through the firewall, check out this top pic especially - you can see where the top stud is in relationship to the expansion valve. The bottom stud is opposite it. I had to dig at a lot of the firewall mat to expose them, but they're both within an inch or so of the valve.



      Good luck with your repairs!

    24. Semi-n00b Tiger351w's Avatar
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      06-22-2011 02:34 AM #59
      I wanted to add to the pictures by EndersM. I also have cable controls and do not have climatronic in my vehicle. I was able to replace the heater core WITHOUT discharging the A/C.

      1. I removed the Dash following the instructions in the Bentley Manual and from this thread.



      2. I removed the instrument support bar again following the instructions on this thread. here is a close up picture of the bolt that is underneath the cowl vent and behind the wiper motor.



      3. here are the two missing pictures from previous posts showing the two bolts located at the A/C expansion valve. Note: there is a doubling plate that might come off when you remove the heater box from the inside of the car. Be sure to put it back in place. You can see it along with the 2 nuts in the following pictures.





      4. As you can see in this photo, I was able to get the heater box loose enough and gain enough room to remove the heater core without evacuating or disconnecting the A/C.




      I want to thank everyone who posted to this thread it made my job easier. Not necessarily shorter. It still took almost 8 hours to do the job by myself.

    25. 07-02-2011 03:50 PM #60
      First of all, thanks for the write-up. I've been doing research on this job for about a week and just now came across this. I don't believe I found this stickied to the MK4 facts.

      Anyways I have a couple questions about the job. My main purpose is to access the HVAC box to repair the flaps that have lost all of the foam. Still don't know if I have a complete box or separate. If I need access to the HVAC box for flap repairing, is it assumed than that I must disconnect the AC lines (must be evac'd then)? For the people that have done the flap repairs already, do you mind posting with what you used and how well u think it's holding up? Would u recommend the product?

      Also, not sure how to drain the coolant exactly. I found a decent write up on how to drain just about all of the coolant, do I need to take it that far? If you just pulled the hose off that connects to the heater core w/ a catch pan would that drain the minimal amount required? I don't have a faulty heater core (going to replace anyways) and didn't add any contaminates to the system so I'd like to recover all of the coolant and keep the draining job to a minimum. What's my best route to take on this? Many thanks if anyone has the answers to my questions.

      Also, a little confused about the step 10 w/ the knee absorber. I have '00 Jetta so I assume I have this. I don't fully understand what this part does and why I need it. Are you saying it's useless and I can just take it out completely? I don't have a doner 'bigger' glovebox yet but that doesn't sound like a bad route. Can I take the piece out and swap gloveboxes at a later date?
      Last edited by Shouse; 07-02-2011 at 04:44 PM.

    26. 07-10-2011 01:29 AM #61
      Ugh, in the middle of this now. I have a question on:
      9) Remove the footwell vent manifold. It appears there are multiple versions of this duct (the Bentley has a picture which does not match mine) but it basically clips in to the heater box. Once it is off, remove the rubber connect at the bottom of the main manifold, connecting to the lower air ducts.

      I see the footwell vent manifold. I don't see any clips. It seems like it just manifold just slides into the main portion of the box and is held in by the sheer overlap of plastic. Anyone provide pictures, comments on this issue. I do have the split box. I'm continuing on and skipping this step for now but fear I'll face this in the end.

    27. 07-11-2011 01:28 AM #62
      Just to add to the facts, my HVAC did not have clips for the lower AC manifold. I Had to lift the main box up and over the lower AC manifold, and then remove the box w/ someone holding the passenger metal bar out a little. Came out real easy.

    28. Member
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      08-10-2011 02:37 PM #63
      Great wright-up. Lots of info here.
      Replacing the leaking heater core. I have a clips. Right now the heater box is out. While there I will fix that blend doors. Glad it easy when the heater box out of the car.
      But I also really want to fix this door on the pictures below





      Is this door has a holes like the metal blend doors in the Heater Box or it's solid like the plastic door in the Heater Box? Because if it solid I can just remove that nasty foam and be done.
      Also, in case I will take that second half peace of HVAC unit (the one with evaporator), does evaporator has any oil inside? I mean, I feel ready myself to evacuate the AC and disconnect evaporator only if I don't have to add oil in the AC system. I can do vacuum and recharge it later, but don't know how/how much to add oil.
      Will be glad to clean this also




    29. Member oldcarguy85's Avatar
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      08-23-2011 11:14 AM #64
      good write up -- thanks. jsut did this job on a 2000 vrg glx with climatronic. Did not have the case split. but ITS DOABLE WITHOUT DISCONNECTING THE AC. Granted, i probably put a godo bit of stress on teh a/c lines, but you can flex the whole box out enough to slide the heater core out. Just have a friend hodl the dash insulation out of the way. Not really a horrible job, just takes a while, and since these cars are getting older and the plastic is now brittle, you will innevitably break stuff during the job.

    30. n00b
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      09-05-2011 05:05 AM #65
      Completed the heater core replacement yesterday. It was quite time consuming but I divided it to several days. No bigger problems occured, just need to makse sure you've got all the tools before you start and you know the locations of all the scewa and studs.

    31. 10-19-2011 10:03 PM #66
      Just completed this a few days ago on 99.5 vr6 with climatronic everything went smooth until i put it all back together only to find out Climatronic head-unit is not getting any power(head unit works fine in another mkiv). Check fuse 5, 25 and ground all are good. Direct power to the blower works not sure what I'm missing. Did anyone else experience this??

    32. Member Albertkvw's Avatar
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      10-19-2011 10:15 PM #67
      my heat blows warm not hot, my ac blows cool not cold. flushed the heater core, recharged the ac and no change. thnking its the blend door... stuck in the middle position. what do you guys think?? going to rip all that out when i start the build so not a big deal for me just wondering.

    33. 11-06-2011 04:54 PM #68
      Just did this on my 2000 Jetta VR6 non-Climatronic with the case split. Wasn't too bad (though there was a fair amount of cussing) but there is one issue: with the heat on full blast I can smell melting/burning, but there is no fog on the windows and no coolant smell. I know the smell of a leaking core quite well ( mine was leaking for a good 3 months before I bypassed it and kept the air temp on cold) and its not a coolant smell. Anyone have any ideas?

      The new core I received from MJM had a thin strip of foam around the edges and a black piece of plastic at the bottom (its the B revision). The core wouldn't fit with the black plastic piece, so I removed it. The leaky core I took out didn't have this piece either. The foam around the edge was held on by some really tacky adhesive, perhaps that's melting. Thoughts?

    34. Member
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      11-06-2011 09:23 PM #69
      I have the same problem.
      I bought mine from MJM too. Also removed that bottom plastic piece. And removed that foam on the sides too.
      Have the same smell you talking about. Definitely not a coolant smell, no fog on the windows...

    35. 11-06-2011 10:02 PM #70
      So I take it the smell hasn't gone away or lessened at all? I'm not looking forward to ripping all that apart again. Did you remove the glue that held the foam on too, or just the foam?

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