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Username Post: 89 k2500 4x4 5.7 heater issues        (Topic#348515)
Karie_ann1977 
Forum Newbie
Posts: 12

Age: 40
Reg: 09-25-17
12-02-17 12:42 PM - Post#2716645    

My heater only blows cold air. The heater core is not restricted. The intake coming from the heater core is restricted. Any ideas or suggestions greatly appreciated!



 
Low priced Genuine GM Auto Parts
454cid 
Frequent Contributor
Posts: 2468
454cid
Age: 44
Loc: West Michigan
Reg: 02-18-12
12-02-17 01:26 PM - Post#2716652    
    In response to Karie_ann1977

  • Karie_ann1977 Said:
My heater only blows cold air.



Not good, I've gone through partial winters that way. Not fun. Usually do to a leaking/bad core that I had to bypass.

  • Quote:
The heater core is not restricted.



You're saying it gets hot?


  • Quote:
The intake coming from the heater core is restricted.



Are you saying the air is restricted from getting to the heater core? If so, it sounds like it's a blend door problem. That's not something I've had to deal with, so others will be better help to you.

99 K3500 RCLB


 
Karie_ann1977 
Forum Newbie
Posts: 12

Age: 40
Reg: 09-25-17
12-02-17 01:36 PM - Post#2716654    
    In response to 454cid

There are 2 hoses one goes between the heater core and intake and the other between heatter core and the radiator neither gets hot



Edited by Karie_ann1977 on 12-02-17 01:38 PM. Reason for edit: No reason given.

 
raycow 
Honored Member
Posts: 27084
raycow
Loc: San Francisco, CA
Reg: 11-26-02
12-02-17 02:10 PM - Post#2716659    
    In response to Karie_ann1977

If neither hose gets hot you aren't getting any flow. Disconnect both hoses at the engine end and blow through either one. DO NOT use compressed air or else you may rupture the core. If you can't blow through, you may have to open up the heater for a look. I am suspecting a control valve in series with the core which is stuck closed, but I don't KNOW this to be the case for sure. Someone else here might suggest a better way to find out.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Karie_ann1977 
Forum Newbie
Posts: 12

Age: 40
Reg: 09-25-17
12-02-17 02:48 PM - Post#2716661    
    In response to raycow

I was able to blow air through and I flushed with garden hose to be sure it was clear. Thanks for your help maybe someone else will know something we are missing.



 
454cid 
Frequent Contributor
Posts: 2468
454cid
Age: 44
Loc: West Michigan
Reg: 02-18-12
12-02-17 04:54 PM - Post#2716676    
    In response to raycow

  • raycow Said:
...I am suspecting a control valve in series with the core which is stuck closed...



GMT-400's don't normally control coolant flow through the heater core. I think it's normally SUV's that actually uses them, but maybe crew cabs, do as well. Rockauto lists one for my truck, I believe, but it's never had one, and I bought it with only 6K miles. Some people also add them..... been wanting to do it for years, but never have.


99 K3500 RCLB


 
454cid 
Frequent Contributor
Posts: 2468
454cid
Age: 44
Loc: West Michigan
Reg: 02-18-12
12-02-17 05:01 PM - Post#2716678    
    In response to Karie_ann1977

  • Karie_ann1977 Said:
I was able to blow air through and I flushed with garden hose to be sure it was clear.



Well that's a good sign.


  • Quote:
Thanks for your help maybe someone else will know something we are missing.



Has this just started happening, and is this the first you've needed the heater this season?

What's the coolant temperature gage doing? Low temperature and the air won't be hot at all, and low level will mean it will be intermittently warm/hot and the gage needle will rise quickly and then drop suddenly.


99 K3500 RCLB


 
rockfangd 
"4th Year" Gold Supporting Member
Posts: 2280

Age: 31
Loc: Utica ny
Reg: 04-13-10
12-02-17 06:40 PM - Post#2716682    
    In response to 454cid

is your coolant full?
Has it been purged?
If both are good then take off the line from the intake at the heatercore and check for flow.
Also inspect the pot metal fitting at the intake. If still present.
find out where the return line goes.
It will either go to the waterpump or the radiator on the passenger side at the top

Old School GM fan FOREVER


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-03-17 06:29 AM - Post#2716721    
    In response to rockfangd

  • rockfangd Said:

Also inspect the pot metal fitting at the intake. If still present.



That is the next place I would look.
The hole in the bottom of the fitting could be plugged.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
rain_man_rich 
Contributor
Posts: 124

Loc: Grants Pass, OR
Reg: 02-09-14
12-03-17 06:45 PM - Post#2716798    
    In response to Chevytech

You could, but please be careful, take the top hose off the connection at the firewall (I believe this is the inlet to the heater core). Then start the truck up to see if it pumps water through the hose. Again, please be careful.




 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-04-17 01:10 PM - Post#2716870    
    In response to rain_man_rich

I had an old f150 this happened to. Turns out someone had put stop leak in it and the inlet INTO the radiator from the heater core was clogged from rust build up and stop leak. I poked out the clog and flushed the radiator and that took care of the problem.



 
Low priced Genuine GM Auto Parts
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