Well, I went and pulled the dash out and replaced the heater core. What I hoped would be a 5 hour job turned into a 17 hour marathon of screws harnesses and vinyl.

I did learn quite a few things while the dash was out and these things may or may not help anyone looking to do the dreaded heater core replacement on their blazers.

I do feel that I need to warn you. There is a good chance that your blazer may be a bit more different than the blazers mentioned in this forum or elsewhere as I have learned, the more options are in the blazer the more harnesses/panels/obstacles you may have to contend with when your pulling the dash out.

I had auto climate on mine and that may or may not make a difference. I have a 2000 blazer LT with tape deck in center console. I could not for the life of me figure out how to take out the damned thing and opted to work without taking it out. I did not remove the seats.

I also did not have to drop the steering column as others have suggested though there were some brackets with four 10 mm bolts connected the dash to the chassis under the steering column that need to be taken out as well as the 2 10 mm bolts under the dash behind the panels: one on each side of the dash assembly (one is accessed behind the glove box on right side). There are also a few 7mm screws to remove on the dash under the speaker panels and defroster panel.

I removed my radio and ac/heat control unit to give more room to reach into the dash and survey things. You may not have to do that. Some have taken the dash out and disconnected it then. I also disconnected the odometer/instrument panel as the dash will come out easier over the steering wheel.

The panels at the bottom aren't too tough to pull out. Just keep checking for screws way back there under the dash if you feel you have them all and it still isn't coming off. You will have alot of panel screws. I kept the screws for each panel with that panel so as to keep track.

Once the dash is loose, you can start looking to see what electrical harnesses you have to remove. The main harness under the blower motor vent behind the glove compartment was disconnected by loosening the 7 mm nut and pulling the 2 blue locking keys out and then wiggling it free. You may also have to unscrew the fuse connected on the driver side as well as the computer OBD-2 connector on one of the panels under the steering wheel.

With everything disconnected, you should be able to pull the dash out. Keep an eye on the driver side as the dash may take out your hazard switch as it swings free of the railing (ask how I know).

Now, some have said that there are 2 10mm bolts to remove behind the passenger side fender and recommend dropping the fendor just enough to get to it. Looking back, I couldn't see a reason to and in hindsight I may have wasted time doing that.

If the heater assembly won't come out and everything else is loose feel free to do that.

Instead, Try to just get the 2 screws on the engine side firewall by the heater core connector (one on the right and one on the left/bottom area besides the evaporator cover) as well as the bolt in the evaporator by cutting and using a ratchet wrench. Keep in mind that there is also another 10mm bolt on the cabin side of the firewall under the heater assembly that needs to come out.

Now here is the part I couldn't find info on and had to wing it. There are two tabs - one on each side of the 10 mm bolt cabin-side firewall under the heater assembly. It seems the bolts can be wrenched loose on the engine side of the fire wall....I never found them. Instead, I tore those bastards loose. Don't do what I did. Use a dremel as you may have a hell of a time getting the heater assembly back in line to get the bolts back in and torn tabs make it all the more harder.

That happened to me and must have added a good 2 more hours trying different ways to get that damned bolt to thread cause the tabs were in the way and would seat right as would a strait rotory cut would have.

With everything loose you should be able to pull out the heater assembly by disconnecting a few choice vacuum lines and some more connectors. The cooling line connectors on the new heater core will have some play so you can get it in there correctly. Make sure that you hook the two vent looking connectors going into the carpet before thinking the heater assembly is working your nerves. For some reason the heater assembly connects to the floor vents which in turn connect to mounts under the carpet.

Now just reverse what you did. Some things to keep in mind.

-The rear wiper/gate open switch wire can and will get caught when you put the dash back in. Keep it loose.

-There is a connector for the actuator motor on top the heater assembly against the firewall. Connect that before you bolt in the dash. I had small fingers and finagled it in by luck and prayer.

-Make sure you connect your courtesy lights for floor lighting back to the panels you took them off of.

-Your passenger side door sensor may or may not have a wire. Try to see if it does before you get started so you don't worry about it and take the dash apart again trying to find it before giving up wondering if it even existed.

-You will need a friend to help put that heater assembly back on the firewall to get all the bolts to thread. You will also need some dexterity to put that one bolt in the evaporator housing back in.

When you have everything back together again hook up your cooler lines to the heater core and open up the radiator cap/reservoir cap. Turn on the engine and make sure you get all the air out of your cooling lines.

The automatic Climate control may need to relearn temp parameters or at least it seemed to the first few drive cycles.

Remember, this was for a 2000 blazer LT 2WD with all sorts of options installed. It may differ just a little from your setup or it may be completely different. Either way I hope all this info I learned and have transferred to this post will help any who doesn't want to pay money to get it done.

Unfortunately, I didn't take any pics. I seriously think I invented a few more cuss words over the course of the repair, But it feels good to have heat for the cold season as well as pride in having no screws left when it was finished!

EDIT: Make sure when you put the dash back on that there are no cloth/felt flaps covering the metal screw catch assemblies that the dash needs to screw in at the defroster vent and speakers. You may inadvertently try to screw and nothing will catch or you will thread in the bottom part of the attachment part. I thought I had it and had to pull the dash out again to fix it as everything was rattling.

 

You've had much better luck than myself. I replaced the heater core on a 1999 Blazer, now nothing works. No heat/ac, no winshield wipers, no dash gauges, and a few more problems. I undid the screws from the evap cover and the one on the firewall, pulled it away and pulled the core out (after dash disassembly). Put new core in, conntected hoses in engine compartment.
The only wired connections I found was the main harness on the passenger side. I didn't pull the blue tabs, just pried it apart after unscrewing the nut. I believe there was another connection behind the headlight selector on the drivers side.
I'm desperate for help as my Blazer is in pieces and doesn't function correctly.

 

I can't say for sure as each vehicle may be different. It does sound like you need to check the vacuum lines behind the dash going into the heater assembly. They look like electrical wires but you can squeeze them. Make sure you check all lines as one may be loose and that would keep the vents from moving to change air flow. Make sure your A/C control unit is hooked back up as well. It may not be connected fully.

I am not too keen on the electrical issues though. I would follow the guidelines given in your original post regarding those issues. Take a close look at all connectors and double check any crossed wires. Make sure your grounds are good as well.

Electrical issues require persistence more than anything. You really have to be methodical in your troubleshooting. Make sure you have all your harnesses connected. Some can hide on you once the dash is put back in.

EDIT: NVM I found some images regarding the repair.

 

Thank you for the narrative.....I'll be attempting this on my 99 Bravada real soon. It's currently bypassed, but the weather is getting colder. Will post some results shortly thereafter. Or maybe I'll just get rid of the thing. It needs a new windshield and tires anyway.

 

I did my 2000 LS last year. Man, the 2 bolts down the bottom were a pig to find. i didn't realize how much of a contortionist you could be to get to them. And I work on C130's which have bolts in stupid positions. They attach to 2 brackets that hold a heat shield on that deflects exhaust heat away from the air con unit. I fitted a new one as it had dissappeared. the dealer had never seen one before and wondered if my find would cure a few air con problems they had with other customers cars. I used the write up from the Haynes manual as well as various posts. Nothing was exactly the same. I didn't get heat first thing. i found I had left a cable off obviously in an awkward position.

 

I'm afraid to do mine, lol. Too much to possibly go wrong. I'll either attempt it, or chicken out, and pay someone to do it, lol.

 

In the middle of it right now. Taking a coffee break. I appreciated your comments; I am using, or rather NOT using, the Haynes manual I have, since nearly the entire dash removal is for vehicles older than mine, a 2001 2wd LT. I have the auto climate control as well. I have the speedo, climate control, panels, bezel, radio and a dozen bolts out of the dash so far. I'm taking pictures like a maniac, labelling everything, and recording notes of the steps I've taken. Wish me luck!

 

Well, it's all out except those two firewall bolts hidden away. I was wanting to do it "right" by pulling the fender well and whatever else I had to do to get to it, but at this point, I'm getting the dremel.

The only major issue I ran into was the wiring to the cassette. I couldn't figure out how to get it out either, so I couldn't unplug the wiring at the cassette. I ended up weaving the three wiring harness sockets on the other end of the cassette cable through the dash and left them all in the Blazer.

When I yanked the main harness behind the glove box, I pulled those blue plastic deals off, but I'm wondering if I needed to. After unplugging it, I couldn't see what difference it made with the blue "combs" out.

I didn't drop my steering column (but of course did lower the tilt function) but I think if I had a good wheel, I would in the future. The black rubber skin is already coming off on top, but if it was a nice wheel, I wouldn't have risked it.

I have taken tons of pictures and written my notes as I went. I did find there were bolts I didn't need to take off behind the instrument cluster, radio and climate control module.

The absolute worst part of this so far has been the bolt inside the heater box. I cut out the service opening on top, and unbolted the plate underneath the skin. There was a filter screen in there to the left which was sitting on top of the washer that comes off with the bolt. It was hard enough getting the socket into that little hole (eventually I just took a deep socket off, scraped my hand into the hole, and unscrewed it manually) but ever turn it got harder because the washer was compressing the filter. Ugh.

I think I'm quitting for the night. I was hoping to get the core out as my quitting point, but I figure I'm more than halfway.

I have 6 hours into it, taking tons of pictures and labeling everything, and I've never done it before.

 

Just started trying to get the dash out today. Have a 2001 LT with climate control as well. No book, can't find it, not going to buy another one. The heater core has been messed up for some time and I already knew it was going to be a several day project so I waited till now to even try and start this. I have the week off and hope to get the new core in and everything back together by Christmas. That's the plan anyways.

So for the info from this thread has been helpful. Adam, I am really wanting to see how your 2001 comes out since you have the same type of Blazer. Probably should take a few pictures myself.

 

I think when my heater core starts to leak in my 2000 I will bite the bullet and pay the dealer to do it. I am usually not afraid of big jobs but this scares the hell out of me. So many things that could go wrong. I like everything to work as intended. I have done the heater core in my 89 Jimmy but that is a piece of cake compared to what is involved with the 2nd gens. If I can't afford it I will connect the two hoses together untill I can.