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Author Topic: 2003 1500 Z71 - Heater Blowing Cold Only.... Unless it's turned to 90  (Read 4607 times)
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stonefan
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« on: 12/18/10 09:48 PM »

OK I'm stumped....

2003, 1500 Z71, Dual Air Control.

I've disconnected the battery, reconnected... turned the key on and left the controls alone to reset.... 5-6 different times with as many combination's...   

I've changed the blend door actuator. Which I don't think it needed.

I've checked the upper and lower hoses at the firewall / heater core... Both Hot/Warm Normal?

No smell or dampness inside the cab.

The truck is not overheating...

I have the appropriate amount of 50/50 coolant/water..

I put in a new Blower Motor Resistor in, which it needed, 2 years ago so I doubt that's the problem?

The main control seems to be controlling all the other functions.. Fan speed, Defrost etc... Just COLD air.

It is NOT Hot on one side and Cold on the other... Just COLD on both sides unless I set to 90

Could it be the internal heat sensor which is on the headliner over my left ear???

What am I missing??? Any help will be greatly appreciated.

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MS03 2500
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« Reply #1 on: 12/18/10 09:56 PM »

Did you turn the HVAC off before you disconnected the battery.
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snowfann
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« Reply #2 on: 12/18/10 10:19 PM »

Did you turn the HVAC off before you disconnected the battery.

Yep... But just to make sure I just tried it again... Same result... Cold air only.
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stonefan
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« Reply #3 on: 12/18/10 10:25 PM »

Did you turn the HVAC off before you disconnected the battery.

Sorry I used my old screen name "snowfann"

Yep... But just to make sure I just tried it again... Same result... Cold air only.
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« Reply #4 on: 12/18/10 10:28 PM »

Hummmm

The only thing I can think of is the heater core or some sort of blockage in the heater core hose.  It's a bit late so I'll post sunday.

You can't have 2 logon ID that is against the rules of the site.
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stonefan
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« Reply #5 on: 12/18/10 10:47 PM »


You can't have 2 logon ID that is against the rules of the site.
[/quote]

I couldn't recover my snowfann password... I kept getting an error... When I typed in my email it said it didn't exist... Soooo I got a 2nd ID so I could ask the question about my heater.... I don't want to break any rules... I'll delete stonefan after this post dies out...
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« Reply #6 on: 12/18/10 10:53 PM »

It's not a issue don't do any thing.  Thumbs up!
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stonefan
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« Reply #7 on: 12/21/10 01:22 PM »

Any other ideas??? Anyone?
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Z66 BUTCH
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« Reply #8 on: 12/21/10 02:50 PM »

It sounds like the heater core is blocked. You didn't say how many miles are on your Avalanche or if any maintance was done on the cooling system or what the outside temps are where you live. If it is cold enough outside maybe a stuck open thermostat could be the problem.......
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stonefan
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« Reply #9 on: 12/21/10 03:53 PM »

It sounds like the heater core is blocked. You didn't say how many miles are on your Avalanche or if any maintance was done on the cooling system or what the outside temps are where you live. If it is cold enough outside maybe a stuck open thermostat could be the problem.......

Hey Butch... Thanks for the feedback.

It has 104,000 miles on it. I did replace the water pump at the end of the summer and while I was at it I changed the thermostat and belts too. After the water pump change I put in fresh coolant and water 50/50... I topped it off a few days later and have added a bit over the last couple of weeks or so thinking the problem might be low coolant. The temps have not been too bad mid 30's...

Could it be an air lock? Both hoses going into the firewall are hot when the car is at temp... If it is an airlock or blocked heater core how should I proceed?
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Z66 BUTCH
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« Reply #10 on: 12/21/10 10:34 PM »

I am wondering why you need to keep adding coolent? First make sure that the cooling system is full, if low you will not get enough heat. I have heard of our engines getting air lock but if both heater hoses are hot I doubt that is the problem.

I do not know how to remove the heater core but it may need to come out if it is plugged. You may be able to rig up some garden hose after removing the heater hoses. Give some short burst of water from a hose a few times and then reverse the direction and try again until it runs clear.
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stonefan
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« Reply #11 on: 12/22/10 10:47 AM »

I am wondering why you need to keep adding coolent? First make sure that the cooling system is full, if low you will not get enough heat. I have heard of our engines getting air lock but if both heater hoses are hot I doubt that is the problem.

I do not know how to remove the heater core but it may need to come out if it is plugged. You may be able to rig up some garden hose after removing the heater hoses. Give some short burst of water from a hose a few times and then reverse the direction and try again until it runs clear.
[/quote

The extra coolant I added was a day after I changed the water pump... Then I topped it off a week or so later... I have not needed to add any coolant since.. Everything is normal with the coolant level.

Would I get heat why I turned the temp to 90 if the heater core was blocked?? Would I get heat at 90 if the thermostat was stuck???

I will try the heater hose removal and flush the core with a garden hose... Nothing to loose at this point.

Do you know if there is an external temp sensor that works with the HVAC? Location? I'm also thinking it might be the internal temp sensor... any thoughts?

This shouldn't be this hard .....LOL
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stonefan
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« Reply #12 on: 12/22/10 12:13 PM »

PROBLEM SOLVED! Cheesy Cheesy Cheesy Cheesy

It was the internal temp sensor... My neighbor who put the thought in my head about the sensor was right.. I thought he was wrong... Roll Eyes

We pulled the sensor out ... Which in retrospect we think we may not have had to do, and blew some compressed air onto it cleaning the dust off that had collected since 2003. Plunged it back in and PRESTO! The heater worked fine.

Soooo.... If you run into this issue one thing to try is blow compressed air up into the sensor for a quick, easy, cheap fix. Cheesy

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« Reply #13 on: 12/22/10 01:02 PM »

Is that the little button that looks like it a mini speaker above the driver's head? Glad you got it fixed.
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stonefan
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« Reply #14 on: 12/22/10 01:13 PM »

Is that the little button that looks like it a mini speaker above the driver's head? Glad you got it fixed.

Yep... That's it.... Looks like a pepper pot.. A good vigorous compressed air blow-off through the holes should remove the built up dust and get it sensing again.... if the problem was the same as I had. 
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gc161968
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« Reply #15 on: 11/10/11 11:19 AM »

Ive been having the same issue im going to try this tomorrow! Sometimes when its blowing warm and I turn it blows bursts of cold air? Very odd I almost thought about air trapped in the system somewhere. Usually I need to keep my temp dial at the max for a long time before I can turn it down.
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rparrish22
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« Reply #16 on: 11/22/11 12:47 AM »

I know this is an older post but I was wondering if this is still working for u. My truck is having the exact same problem. I did all the resets, battery pulls and fuse pulls and it did not fix. I am trying this later today and I hope it works.
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« Reply #17 on: 11/24/11 12:16 AM »

did not work. I'll have to try something else. Does anyone out there have any other suggestions as to what this might be?
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« Reply #18 on: 11/24/11 02:29 AM »

So yours is blowing cool air also.
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rparrish22
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« Reply #19 on: 11/27/11 02:05 PM »

Yeah cold unless 90 degree setting. Found out my temp sensor was missing. Replaced it but it was reading 134 degrees when it was 70 degrees. Tried to flash the latest code to the climate control  and froze it up. Cannot write to these ones. Replacing climate control head soon and will see if that helps.
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« Reply #20 on: 11/28/11 06:04 AM »

Looking thru the manual it recommends you try it. You have not disconnected anything so you ignore anything about connecting and disconnecting


Important: Do not adjust any controls on the HVAC control module while the HVAC control module is self-calibrating. If interrupted, improper HVAC performance will result.

Alternate Method (w/o Scan Tool)

•Clear all DTCs.
•Place the ignition switch to the OFF position.
•Install the HVAC actuator.
•Connect all previously disconnected components.
•Remove the HVAC/ECAS fuse for a minimum of 10 seconds.
•Install the HVAC/ECAS fuse.
•Start the vehicle.
•Wait 40 seconds for the HVAC control module to self-calibrate.
•Verify that no DTCs have set as current DTCs.
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rparrish22
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« Reply #21 on: 11/28/11 09:16 AM »

Yeah that was one of the first things I tried. I tried it a few times and didn't work.
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« Reply #22 on: 11/28/11 09:24 AM »

Some folks have tryied cleaning the Cabinet air temp sensor that's the thing above the driver head it looks like a speaker. Try blowing air through it.
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