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Suburban Rear Heat Not Working

Sven, THANK YOU!!! I just spent some time tracing lines, as best I could, and I was about 80% sure there is no valve. Those schematics are GREAT! It confirms what I was finding. Thanks!

So, AF should always be going through the rear core (and front). They are simply a loop.

Now here's the problem: I tore the rear, inner quarter apart. The blend door works fine - I visually confirmed this. When turning the temperature dial, the blend door simply opens and closes to allow more/less air to go through the rear core. The door actually does double duty since the blower motor blows air through the A/C core first, then the Heater core**. Air always goes through the A/C core; the door determines how much air then goes through the Heater core.

Using my hand and an IR gun, the lines to the rear core never got above ambient (although the supply did a few days ago... weird). Just to be sure, I also checked the rear core - same thing - ambient temp.

So, even though I can push fluid through the rear supply and return lines (from engine bay), there must be a blockage in them, right? The only thing I can think of is that since fluid will take the path of least resistance, it will go through front core only if there is even a slight blockage in the rear. The pressure supplied off the T-stat must not be enough to over-power the blockage (as I was apparently able to do with the hand-pump).

I'm going to disconnect the heater lines back by the tailpipe and also in the engine bay. This will isolate the lines completely - and also isolate the core. I'll try flushing with very little pressure (maybe just pour some water through the lines) to determine which is clogged.

It appears where coming back to the suggestions above that mentioned clogged lines.

FYI for those that don't have rear heat... The supply line for Heating first comes off the T-stat housing and then goes to a "T" where the supply line splits and one line goes to the front core, the 2nd to the rear core.

**This is also why air comes out of the rear vents with more intensity when the Temp dial is on cold as compared to hot - the blend door closes off the Heater core - air doesn't have to be pushed through two cores. It also appears the air can take a slightly more direct path when not going through the Heater core.
 
Well, I'm 'bout done with this.

I started to disconnect the quick-connects back by the tailpipe (directly under the rear core, but on the outside of the vehicle - above the tailpipe). But, then thought better. I don't have the special tool (if one is even made) and the local parts stores didn't have one - at least not the ones open today. Rather than try to push those 11-year old plastic tabs in with a mish-mash of tools and risk breaking it, I skipped that step.

Instead, I slipped the rear lines off of the "T's" in the engine bay. With a long funnel inserted into the supply line, I added some AF. With just gravity doing the work (about 1' above the top of the rear core) AF came out of the return line.

To me, that means there is no restriction. Does this sound reasonable?

Any other ideas?

The kids only sit in the middle row and they get enough heat from the front.
 
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did you flow the fluid thru the rear core in BOTH directions? If there was a inlet obstruction,, it could be removed by flowing the fluid backwards thru the system.
 
Pruittx2 said:
did you flow the fluid thru the rear core in BOTH directions? If there was a inlet obstruction,, it could be removed by flowing the fluid backwards thru the system.
Click to expand...

Yes. I have actually now flushed it numerous times. But, the first "official" flush I did with the garden hose was done backwards to avoid possibly pushing a clog further into the core. That's the one where I got a tablespoon or two of sediment/crap out.
 
dangerousdave said:
The stock metal lines are subject to corrosion.
When you flushed out a tablespoon of crap, then it seemed to flow, that's a sign.
On my previous 'burb, I replaced the stock lines with copper, and was able to Prestone superflush the system back to fucntion. I got lucky on that one.):h
Just my $2.50, for inflation.
Click to expand...

You might try a $5 valve from the hardware store to control restriction to the front heater core slightly, trial and error adjustment. Kind of a rig around replacing the lines, fittings, etc.
 
dangerousdave said:
You might try a $5 valve from the hardware store to control restriction to the front heater core slightly, trial and error adjustment. Kind of a rig around replacing the lines, fittings, etc.
Click to expand...

Are you thinking of a shut-off valve installed in-line to the front core and then just experiment with how closed-off I turn it? Or, is there a different valve you had in mind? That's a great idea.


David: I just replaced the pump when I did the engine - about 10K ago. I bought the HO pump from NAPA - at least it had "HO" stamped on it. I wonder if there is any way to test how much a pump flows?
 
Sounds l8ike a flow issue here to the rear core. The diesel BURBS will not get good heat from the rear when idling or running at low RPM's either. Start off by taking the 2 black plastic tees out of the heater lines where they branch the flow to the front and rear cores. Make sure the restrictors inside of them are not plugged. Most don't know that those 2 tees are special pieces that have a flow restrictor to balance the flow from front to rear. If you don't run those special tees you will only get rear heat and the front won't make much of any. After taking the tees out get your garden hose and back flush the 2 cores seperately. The way you did it by hooking up the return at the radiator will not give you hardly any flow to the rear core. Also like mentioned there could be some scale or corrosion trapped in the rear cores lines that will block the restrictors in the tee once coolant begins to flow through it. By removing the restrictive tees and flushing you can now flush out that debris without it getting caught in the restrictor. Once you have flushed the 2 cores out both ways reconnect the tees and refil and purge air out and then check to see if your lines at the rear core are getting hot when you feel them. Chances are though flushing the cores out individually will correct your problem or tell you if you have a plugged core.
 
THEFERMANATOR,
I replaced the tees that you are talking about with NON-factory ones (no restrictors) and my heat works just fine in the front and rear. Maybe I don't know what tees you are talking about. I replaced the ones in the engine compartment, just above the intake manifold on the passenger side.

They crumbled in my hand when I touched them!

Todd
 
THEFERMANATOR said:
Sounds l8ike a flow issue here to the rear core. The diesel BURBS will not get good heat from the rear when idling or running at low RPM's either. Start off by taking the 2 black plastic tees out of the heater lines where they branch the flow to the front and rear cores. Make sure the restrictors inside of them are not plugged. Most don't know that those 2 tees are special pieces that have a flow restrictor to balance the flow from front to rear. If you don't run those special tees you will only get rear heat and the front won't make much of any. After taking the tees out get your garden hose and back flush the 2 cores seperately. The way you did it by hooking up the return at the radiator will not give you hardly any flow to the rear core. Also like mentioned there could be some scale or corrosion trapped in the rear cores lines that will block the restrictors in the tee once coolant begins to flow through it. By removing the restrictive tees and flushing you can now flush out that debris without it getting caught in the restrictor. Once you have flushed the 2 cores out both ways reconnect the tees and refil and purge air out and then check to see if your lines at the rear core are getting hot when you feel them. Chances are though flushing the cores out individually will correct your problem or tell you if you have a plugged core.
Click to expand...

The first time I flushed it I did it after the T's (actually, every time I've done it the T's have not been in the circuit). I did both cores. I hooked my hose to the return line from each core and extended the supply line into a bucket. I've since flushed it the other way, as well. If I'm not mistaken, I did it the way you are advising?

I had no idea these T's had restrictors in them! That will be my next task - hopefully tomorrow.

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PS: Sorry about the big picture!
 
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That black plastic tee conected to the green heater hose in your picture has a restrictor in it in the rear portion for the rear heater core. I wasn't able to use them in my swap and just used some brass ones I made up. I ended up having to go back in and put the restrictors in them with epoxy in mine to equal out the heater circuits.
 
DennisG01 said:
Are you thinking of a shut-off valve installed in-line to the front core and then just experiment with how closed-off I turn it? Or, is there a different valve you had in mind? That's a great idea.

David: I just replaced the pump when I did the engine - about 10K ago. I bought the HO pump from NAPA - at least it had "HO" stamped on it. I wonder if there is any way to test how much a pump flows?
Click to expand...

I'll do this backwards, Dennis;
I wouldn't sweat the HO pump flow (if it wasn't working, you'd overheat.
Shut-off valve is fine, as long as it can take the heat.

I hate the plastic pieces the General puts on heated components, so I naturally hate the plastic T's for heater lines. I prefer brass or copper. Making my own T's and fittings is something that has increased the reliability of many vehicles.

Hope I helped. We're on our 3rd Suburban, all w/dual a/c & heat. Sorry it took me so long to reply, Dr. vists, etc.

Sven; great diagrams.
 
dangerousdave said:
I'll do this backwards, Dennis;
I wouldn't sweat the HO pump flow (if it wasn't working, you'd overheat.
Shut-off valve is fine, as long as it can take the heat.

I hate the plastic pieces the General puts on heated components, so I naturally hate the plastic T's for heater lines. I prefer brass or copper. Making my own T's and fittings is something that has increased the reliability of many vehicles.

Hope I helped. We're on our 3rd Suburban, all w/dual a/c & heat. Sorry it took me so long to reply, Dr. vists, etc.

Sven; great diagrams.
Click to expand...

Thank you, Dave. Yes, that does help. :smile5:
 
dangerousdave said:
So, Dennis;
Is all warm and toasty, all over?
Click to expand...

No, not sure yet. Up here in PA we've been having this strange atmospheric condition where water falls out of the sky. I see where you are located, so that probably sounds really weird to you:smile5:

Just kidding, of course! But, actually it has been raining, and coupled with temperatures in the low 40's, it hasn't been very conducive to doing outside work. It's going to be decent this afternoon, but I've got to winterize my boat first. Hopefully there'll be some daylight left - it gets dark by 5:00. Thanks for checking in, though! I appreciate it!
 
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