I could really use some help. I have a new to me 93 chevy blazer and it needs a heater core. How hard is this to replace? I really can’t afford to pay a mechanic to do it right now, I could if I waited about a month. I really think this is something I could do myself though because it sounds easy enough. Any advice would be helpful 
Not familiar with the blazer, but on every vehicle I’ve worked on the heater core was not for the faint of hart. Typically the job involves removing the passenger side dash, the HVAC box that houses the ventilation doors/flappers, draining the coolant, removing the heater core hoses and then removing the core. Quite a bit of work with most of the labor being the removal of the dash.
On some vehicles without AC the core can be removed from the engine compartment in which case the job is much easier, but that is an exception. Most will need the dash removed.
I’ve done this on old Jeep CJ-7s twice. It wasn’t really hard, just a pain in the butt (and they don’t really have a ‘dash’ to dismantle). If it were one of my newer vehicles, I would still attempt it. If you have any mechanical ability at all, you have a good chance of success.
If I were in your shoes, I’d go grab a Hayes or a Chilton’s manual on your vehicle. They will describe how to go about it in there somewhere. Read through the instructions and gauge for yourself weather this is within your capabilities or not.
I’m not familiar with the Blazer core either, but typically, they are a pain in the ass. As has been said, access is the key. It’s basically just a mini radiator, attached to some water hoses, but the sadists in the design department seem to go out of their way to make it impossible to remove.
Get the manual, do a little exploratory investigation, and see if you think you can handle it. If it looks too tedious, buy the core unit from a parts store, and take it to an indy shop to install. It might be worth the few extra bucks to save yourself the headache.
I’ve replaced about 4 heater cores. All of them on 1980’s Mustangs.
On the Mustangs it was a relatively easy job if there was no factory air conditioning. If there was air conditioning it was a bitch.
In a Mini - 20 minutes.
My Xantia took a full day, cost £200 9Not a Dealer - that would have been £350) and burst just less than a year later, flooding the car with boiling coolant.
Fortunately [sort of] the car was a write off after a milk truck reversed into it so just went to the scrapyard.
So, as prvious posts indicate, could be quick & easy, more likely not. As said, check a Hayne’s manual to judge the relative difficulty level for your model before you get into it.
If by this you mean you are willing to go without heat and defrost for a month, you can bypass the core very easily.
The heater core has two 3/4" (usually) hoses attached to it where it sticks through the firewall. The coolant enters the core through one hose and exits out the other so it is simply a matter of re-arranging the hoses to keep the coolant flowing through the hoses without entering the core.
This can be done by either removing the hoses from the core and connecting them to each other, end to end, with a piece of pipe used as a coupling. Or, you can find where the other ends meet the water pump and remove one hose at this end then cut and reattach the second hose so that the coolant is exiting the water pump, travels through 6-8" of hose and re-enters the waterpump.
Any option like this is just a getby and while the core is bypassed you will have no heat, but, it will buy you a little time.
Finally, if you do decide to replace the core yourself, just be very careful of keeping up with all the screws that will be removed from the dash. Forgetting just 2 or 3 screws will have your dash squeaking and rattling over every bump.
thanks for all the replies, I am indeed trying to do it myself. What I meant was that I could wait, was that I can wait, I still have another car, but I won’t be driving this one. Have to have heat. It took me an hour to unscrew about half the screws. Thats because I am a weakling. I am finally starting to see some progress though. I have all the screws and even know where all of them go 
Go me!
The difficulty of heater core replacement varies widely with the particular model and year of vehicle, and sometimes with whether or not it has A/C. A quick glance at my estimator book gives “times” ranging from 1.0 to 7.4 hours for domestic cars and 14.4 (!!) for one model of Mercedes.
For a 93 Blazer, it shows 5.0 (pretty big project). For a 93 S-10 Blazer, it shows 1.6 (not too tough). [hijack]When I hear “Blazer,” I think Blazer. I’ve learned, however, that some people will say “Blazer” when they actually have an S-10 Blazer. Good recipe for getting incorrect information.[/hijack]
On many designs with A/C, the heater core and A/C evaporator are located in the same housing, which has to be removed as a whole before it can be opened to extract the heater core. This means disconnecting the A/C lines, which means emptying the A/C system. If you’re not sure that yours doesn’t require messing with the A/C, you might be better off having a pro take care of it.
In addition to what Gary T just said, venting refrigerant into the atmosphere is not only an EPA violation, it’s going to cost a fair amount to replace the vented R-12, if you can find someone who has it. If you can’t find any, you’ll need to convert the system to a newer refrigerant style. This is not something for a driveway mechanic to attempt. Plus, you can’t legally purchase CFCs and HCFCs without showing your certification card.
I replaced the core in my Ford van last fall, and did not have to disturb the A/C. It still took about 5 hours because everything except the taillights seemed to be in the way.
Good luck.
Thanks again, I didn’t know that there was more than one type of blazer
It is indeed a s10, I am to the point where I am near the core, even though I feel like I had to go through the trunk to get it!
And this is why I don’t eat or drink while here…
Most cars built since the mid 80’s do seem as if the heater core is the first component that’s placed on the assembly line and everything else is bolted to it.
As to Deadly Nightlight’s predicament, all I can do is echo the comments of getting a Chilton or Haynes book (or both - they complement each other well, especially on difficult jobs like heater cores as they often present differnet perspectives and processes to a job.)
Hi Folks, I replaced my heater core, wasn’t too bad of a project, the worst part was reassembling the dash, because all the freaking frames connect to each other. Thanks for all the advice, As I am a clueless chick I normally know nothing about this stuff, and I still can’t tell you the name of most of the tools I used(except the vise grip, because I had to describe to someone what I needed, so I could borrow it) but I got it done, wooohooo!
Congratulations!