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99 Blazer Heater Core Replacement


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sonordrumr
User

Nov 25, 2007, 10:44 PM

Post #1 of 18 (18580 views)
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Tom, first of all, thanks for your great advice, I've read alot of threads and have found them to be very informative and useful. My question is about replacing the heater core on a 99 Blazer. Do I have to take he dash apart or can I just get to it from the firewall? I've done everything I can think of except checking the actuator as my heat problem. Flushed, replaced all hoses except top radiator hose, thermostat, etc. the works! Also, how can I access the actuator "door" to see if it is stuck somehow? Also, do I have to use "Dex-cool" antifreeze? I bought some Prestone that claims it can be used in any vehicle, even Chevy/GM. I appreciate any advice you can give me on this headache I'm about to delve into. You're the man! Smile


Tom Greenleaf
Ultimate Carjunky / Moderator
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Nov 26, 2007, 3:49 AM

Post #2 of 18 (18552 views)
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You do not have to use Dex-Cool and I actually won't use it again in anything. If you read the container it's just EG = ethylene/glycol but just came with a lie that it would outlast the others. Quality of additives is the whole enchilada. The Prestone colorless is at least not going to mess up the different colors which are just dyes anyway.

1999 Blazer Heater Core: Ouch! That is the full size pup like Suburbans - right? If so that's a huge job - whole dash off and hit back if you want to do that and I'll try to scope out some advice from folks who have done several for A/C work and replaced the heater core as it was there in the process so most would toss it.

Hit back with what you want to do with this. I forgot the original complaint with this??

T
_________________________________________
Long retired now


sonordrumr
User

Nov 26, 2007, 9:06 AM

Post #3 of 18 (18545 views)
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Thank you for the reply. Yeah, I'm going to have to replace the heater core. If I had the money, I would pay someone else to do it but....I was wondering where the actuator door is to check if it is stuck somehow. Thanks again!


Tom Greenleaf
Ultimate Carjunky / Moderator
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Nov 26, 2007, 9:36 AM

Post #4 of 18 (18542 views)
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There are more than just one door to divert air flow. What was the original problem or existing problem? Heater core itself should be fine unless it's leaking coolant or plugged solid and can't be flushed out,

T
_________________________________________
Long retired now


sonordrumr
User

Nov 26, 2007, 10:03 AM

Post #5 of 18 (18541 views)
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I'm not getting any heat in the cabin. I've replaced the heater hoses, thermostat, lower radiator hose, and drive belt. Still no heat! I assumed it was the heater core, which I've flushed out. what are the locations of the air diverter's?


Tom Greenleaf
Ultimate Carjunky / Moderator
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Nov 26, 2007, 11:35 AM

Post #6 of 18 (18533 views)
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All these doors either are moved by actuators electrically or by a vacuum diaphragm at the direction of the control panel. As you know it selects hot or cold, which ducts to vent thru and fresh or recirculated air. The amount of heat will be blended as to your liking. I haven't heard of many problems with the doors themselves.

You heater core itself if not leaking and could let water flush thru is not the problem and that's good news for now.

I don't have a blow-up diagram of this whole distribution box or the wiring to and from controls to help us with this. Does this behave as far as A/C and directing the air flow as requested, vents, high and low, defrost vents and floor etc? Even on just asking for "vent" air it probably would let heat thru if you selected vent and the warmest setting. Like many people you probably shut the temp to full cold for the whole off A/C season so the blend door for the heater core has been shut for a while and may just be stuck there. They are just funky choke plates kind of. It's possible to get at this one or others thru the glove box or getting creative with what can get out of the way.

Does it feel like the control knob for temp really changes anything or do you hear anything? Problem could be there?? I think that same knob would give you less cool for A/C request and you would notice that and rule that out if that works that way. Too cold where I am right now to test out anything with A/C as far as how cool it can get.

Test out what you can and let's see if we can pin this down. Again - is this the full size Blazer or the S-10 size? The name got used for both and I don't know which year means which??

It would be nice to get this fixed while in place as I'm almost sure you have to evacuate/disconnect the A/C system to remove the distribution box and then you'd have to know how to deal with thatPirate,

T
_________________________________________
Long retired now


sonordrumr
User

Nov 26, 2007, 12:15 PM

Post #7 of 18 (18530 views)
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It is the S-10 model, the smaller of the 2. The vents all seem to work with the change of the knob from top to bottom. I was on a trip about 60 miles away and had heat all the way there and then on the way home about 4 hours later it was blowing cold air. I had been having electrical problems before and changed the alternator which straightened out the electrical problems but still no heat. Could the low volts during that period cause a relay or electrical powered switch to not work properly now? I will check my manual after work to see of any vacuum or electrical switches to or from the heater. I've checked all fuses and relays and they seem fine visually. The heater core is not leaking at all and when I flushed it a small amount of coolant came out and then clean water. I flushed it from both ways to be sure. Thanks for all your help.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Nov 26, 2007, 2:23 PM

Post #8 of 18 (18523 views)
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Check out this link below! This uses a heater control valve and that's the likely problem and could be a piece of cake!!!! I just searched that out for parts to see if I could find a diagram and stumbled on that! This means the temp is controlled by the flow of water which is adjust by this item. Part might be fine and just getting wrong info. This probably has nothing to do with tearing up the distribution box at all! I'm going to go back there and see if that shows more on that thing. In the mean time check the wiring going to it and connections. The mechanical force should be vacuum not cable and I'll be the default position when no vacuum is available is to shut it off, thus no heat!

http://www.autozone.com/.../repairInfoPages.htm

T
_________________________________________
Long retired now


(This post was edited by Tom Greenleaf on Nov 26, 2007, 2:31 PM)


sonordrumr
User

Nov 26, 2007, 2:43 PM

Post #9 of 18 (18521 views)
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Right on, Tom! Thanks a million! I'll check it out.


sonordrumr
User

Dec 4, 2007, 1:01 AM

Post #10 of 18 (18497 views)
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Just to check back and tell you guys my solution: I picked the brain of our local mechanic and he explained I didn't have the aforementioned heater control valve and that it was only equipped in higher end GM vehicles. After several troubleshooting tries, I filled the radiator and overflow reservoir and finally got some heat albeit lukewarm and intermittent. I decided the water pump was at fault and noticed after using a mirror I was getting a small amount of leakage from the weep hole at the bottom of the pump. I ordered a new pump today and will let you know how things go after install. Thanks!Smile


sonordrumr
User

Jan 5, 2008, 9:20 PM

Post #11 of 18 (18389 views)
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Tom, its me again!SmileHope you have a great new year. I'm still having problems getting full heat in my 99 Blazer. I've checked everything I can imagine and replaced virtually all heating elements except the heater core which flushed out just fine. I removed the coolant reservoir the other day and cleaned it out really well. I found a blockage in the reservoir and thought for sure I found the problem but still only lukewarm heat and sometimes cold. One thing I have noticed is that the ac compressor cycles on sometimes when no call for ac is present. Why? I've also noticed a change in air flow when switching from defrost, front vents, and floor. The floor dramatically drops air flow. Thanks for any help!Unimpressed


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jan 6, 2008, 5:18 AM

Post #12 of 18 (18384 views)
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Hi,

This is getting to be enough to read and follow! Ok: A/C can kick compressor on on defrost or perhaps a mix setting - it does that just to circulate oils to preserve the compressor in off season - doesn't make cold and must shut down when cold or it would kill the compressor. If worried about that just uplug it and tie it off safely for winter. Again - it can't make cold in weather below about 40-50F as the refrigerant wouldn't evaporate at all and it's not designed to be a freezer so forget that for now.

You said you had good water flow when flushing out core? If so then there should be enough left to core to blow decent heat. It could be covered in dirt/dust who knows in there and that could be a problem. I think this is a diverter door problem and you don't want that but let's see if we can smart it out.

If you have a cabin air filter replace it. I don't think this does but do check on that.

Feel the heater hoses with engine warmed up and heater on. Smaller should be hot to the touch and the larger (return) should feel cooler but not ice cold. If both are cold I have to think of something. If both are piping hot then no heat is exchanging at heater core which could be a diverter door/flap not allowing air to flow thru it.

Back to dirt in there possibilities: Has this been exposed to excessive dust, pollen, pine needles etc.? The air flow has me thinking about this. There are some trick without taking the whole vehicle apart if that's the problem.

May want to start a new thread with the "state of the state" now as when these get this long they are hard to follow and know what's already been ruled out. Stay warm,

T
_________________________________________
Long retired now


Double J
Veteran / Moderator
Double J profile image

Jan 6, 2008, 4:40 PM

Post #13 of 18 (18378 views)
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just wanted to jump in with my 2 cents


the a/c compressor will cycle on in the defrost setting to dehumidify the air inside the cabin.
helps on cold days to defrost windows better too.

ever ridden in a car with no a/c or a/c not working, on a rainy day/night....takes forever to clear all the glass


ihaveanothereye
New User

Jan 16, 2009, 2:43 PM

Post #14 of 18 (16456 views)
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Hey guys! I have just come across this same problem. I have replaced my radiator, thermostat, all hoses and the heater core, and I still do not have heat. My car has the exact same symptoms that sonordrumr has.

Once in a while I will feel heat, but for a very short time, then its right back to cool air. I have had many opinions and noone can seem to figure this out...

Any help is greatly appreciated... it's -6 here in Chicago, and this is my only means of transportation, and no heat hurts :(.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jan 16, 2009, 4:39 PM

Post #15 of 18 (16445 views)
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This thread started in 2007!

Please start a new one with your specific vehile and let's go from there,

T
_________________________________________
Long retired now


lldames
New User

Nov 9, 2010, 10:39 AM

Post #16 of 18 (11296 views)
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In Reply To
This thread started in 2007!

Please start a new one with your specific vehile and let's go from there,

T

HELP i have no heat or ac. Themo repalced, flush rad,switched hose Chevy Balzer 2000


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 9, 2010, 12:40 PM

Post #17 of 18 (11292 views)
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What part of start another thread didn't you understand?




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
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Nov 9, 2010, 2:30 PM

Post #18 of 18 (11283 views)
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Only GOD knows HT??

Tom
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Long retired now




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