1999 Blazer blows cold air

I have a 1999 Blazer 4.3.It blows only cold air through heater and defrost.New thermostat, radiator full, i noticed hoses going to heater core 1 hot,1 not. Is heater core plugged? Help Thanks

You don't have any engine temp problems? No over-heating? If not then it sounds like the HC. It will save you ALOT of money to do it yourself. The HC costs about $80. I don't know how much it would cost for a shop to do it but it took me about 18 hours to do it. Most shops charge between $65 to $95 an hour for labor. Of course I've never done before that so I could probably do it faster now.

As long as it isn't leaking, there is no reason to replace the heater core. Most of the time you can unclog them for free, with very little effort. Take the heater hoses loose from the heater core at the firewall, and use your water hose (or "garden hose" or "hose pipe" depending on where you live) to clear it out. Alternate putting the hose on each heater core tube to flush in each direction until the water flows easily through the core. Reattach the heater hoses. Considering that the core is plugged, it would be a good idea to check the condition of the coolant in the radiator to see if the whole system needs to be flushed as well. If it does, this is the procedure that I recommend:

For normal maintenance:

Buy the following:
2 gallons of distilled water $1
2 gallons of antifreeze $20
Prestone Flush 'N Fill kit $3
Prestone Radiator "Flush" $3

Turn your heater on and leave it on for the entire process

Drain the antifreeze from the system.

Install the "T" from the Flush 'N Fill kit and follow the directions that came with it.

Disconnect the water hose, close all the drains, add the Prestone Flush, fill with water, get engine up to operating temperature and run for 20 minutes, allow to cool then, drain the system.

Connect your water hose to the Flush 'N Fill "T" and flush one more time. Drain.

Fill the system with a 50/50 mix* of antifreeze and distilled water. Continue to fill the system over the next few days as the air is worked out of the system.




For clogged, neglicted, or extremely dirty systems:

Buy the following:

2 gallons of distilled water $1
2 gallons of antifreeze $20
Prestone Flush 'N Fill kit $3
Prestone Radiator "cleaner" not "flush" $4

*NOTE - If you can find them, the two part acid flush and neutralizer kits work much better than the Prestone Cleaner. Substitute for the Prestone Cleaner and follow the instructions on the package.*

Turn your heater on and leave it on for the entire process

Drain the antifreeze from the system.

Install the "T" from the Flush 'N Fill kit and follow the directions that came with it.

Disconnect the water hose, close all the drains, add the Prestone Cleaner, fill with water, run the engine 3-6 hours (you can leave it in for a few days if neccessary), drain the system.

Connect your water hose to the Flush 'N Fill "T" and flush one more time. Drain.

Fill the system with a 50/50 mix* of antifreeze and distilled water. Continue to fill the system over the next few days as the air is worked out of the system.


*When you do your final drain and fill....not all the water will come out so to get the proper 50/50 mix you should add the right amount of straight antifreeze then top off with the distilled water.

Good call Blazee. That's why there's other mechanics here.:grinyes: I guess my info would be better followed only if it begins to leak. Do what Blazee said Blazerjtb1999. Let us know how it goes.

Amen on trying everything else before replacing the Heater Core. If you don't have a ton of special tools like LONG extensions, swivel sockets, LONG needle nose pliers, a reversable cordless drill, and a mountain of patience, you will in all likelihood be biting off more than you can chew. I replaced one on an '89 S-10 Blazer and it took over 4 hours WITH the proper tools.

I just had to do the heatercore in my 99 because some moron decided to put stopleak in the system before I bought it. When I finally did flush it all out there was a leak in the heatercore. Took me about 10 hours and was a MAJOR job. To put it into persepective, you need to remove almost everything between the steering wheel and the firewall. PLUS, you gotta take the passenger side inner fender off to get access, PLUS there is one nasty hidden bolt inside the heaterbox on the engine side of the firewall that was just butt-nasty to remove. Nightmares.....

PS: If the intake gaskets have never been changed flushing the engine may take them out as well.

A little trick that will save a big mess, is get about 4' of 3/4" heater hose and 4' of 5/8" heater hose. Remove the heater hoses from the heater core, and install the 4' hoses and dangle them out over the fender. Stick your garden hose nozzle alternately into each one, (as Blazee mentioned), and flush away. A few bursts with the nozzle helps loosen crud too. Flush until the water comes out clear.

My favorite trick is to cut the male end off of an old 5/8 garden hose and attach it directly to the 5/8 heater hose fitting on the fire wall using the hose clamp, then turn the water on and off in bursts. Most munincipal water supplies average about 45-60 psi, so you should get a pretty decent blast of water through the core.

And for the record, I have never ruptured a heater core doing this, and in the unlikely event that you do, that just tells me the core was shot anyway.