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Suburban Rear Heat Not Working

I've been following this thread pretty closely as I have a heater problem on my wifes 00 Burb. Mine's the front heater. Narrowed it down to the heater core needs flushed/replaced. Are there any products you guys would recommend to put in during a flush to really clean it out?
 
have you checked the rear a/c blend door motors for full movement? The rear a/c unit isn't that bad to get to. the third seat has to be removed for access and then it is just removal of rear interior panels to gain access to the a/c heater unit. the two control motors as well as the blower motor are all there for easy access. now if you core is bad/ plugged/internally corroded then it gets a bit costly as the a/c unit has to be evacuated and disconnected to pull out the rear unit fore disassembly to get to the core.
anyways once the unit is visible you can cycle the motors to see if they are functional and going the full stroke.
also now is the time to check the a/c evaporator core and see if it is covered with dirt,hair,small children ect.. from experience on mine the firsttime i looked into it it was full of dog hair, and other crud sucked in from the cargo area. This will hinder your air flow through the a/c core and to the heater core.
oh forgot-- check to see on the blend door if you can hear the door flap opening and closing. I had the plastic square drive of the flap break off the servo motor. the motor was moving but the flap was stuck in one position.
 
dhjunkie said:
also now is the time to check the a/c evaporator core and see if it is covered with dirt,hair,small children ect..
Click to expand...

Now that is funny! :smile5:

Yes, I did pull the interior apart and everything in there looks clean and the doors move perfectly.

I got stuck on my high idle problem - hopefully I'll get back on this one, soon.
 
Suburban Rear Heater Hose Assembly?

We are finally putting together our Suburban fuel economy experiment and we're trying to plumb up the rear heater (and front heater) hoses. Did anyone ever settle this thread with a gm service schematic? We have a '97-2000 vintage like stuff. The Suburban was a '99 gasser 5.7. We bought all factory looking parts for a '99 1500 6.5L. I scanned the later part of this thread one more time. Now I'm gonna look at the pieces and compare to this thread. The only thing I can say for certain at this point is that the QD is not going into this truck!!

Would appreciate any new info on this subject, soon!! Please?
 
DennisG01 said:
OK. Now I'm confused again. I thought it was just going to come down to switching the two lines around that go to the two cores since my rear heat used to work with the current Tee's (they do not have restrictors - I am 100% positive). But, it appears Dave has the same green hose going to the front core -- #2 -- (which I'll assume does not neck down... just like mine). The hose that is currently in the position of "rear core inlet" -- #3 -- does neck down.

So, just to clear things up (for me, anyway) -- according to the numbers in this pic, what sections of the Tee's are supposed to have restrictors?

Ferm... I think you mentioned this above somewhere, but you're 100% positive that those Tee's you have do have restrictors? I just keep coming back to not understanding why everything worked before, and now it doesn't.

Unless, could my restrictors have fallen out? While the engine was out of the truck and everything was disconnected? I mean, are they an actual part of the Tee, or could they come apart?

I really appreciate all the help! Oh, I dream of $.99 diesel, too!!!!

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Click to expand...

If the supply and return "tee" fittings are intended to be identical, then the orifice would have to be in #3 and #6.

What we purchased would make the "tee" fittings the same. I'll have to check with the parts man to revisit what the parts book calls for by p/n.
 
I confirmed with gm parts book that the supply and return "tee" fittings are identical p/n's. Thus, the orifice part of the "tee" is at position #3 and #6 restricting flow to and from the rear heater. I forgot to measure the size of the orifice in the plastic tee. However, the orifice in the QD is approximately 0.260" diameter.
 
NoDak - So you're saying that I should have a restriction going to the rear core? Like JR said, that doesn't seem to make sense, but then I'm not a fluid engineer.

However, for some reason, everything is now working just fine! I flushed out the rear core/lines a few times last year and got good flow through the lines - but never got the rear heat working. The only thing I did a few weeks ago is give the whole system a clean/flush/fill. I don't get it!?
 
Don't let any facts get you (me) confused... if it doesn't act "broken," don't fix it! I suspect the "more" restricted flow for the rear heat may be more important for severe cold weather warm ups? Our project Suburban has fuel mizer pre-cups so it will definitely make heat at idle. So, if you didn't have the orifice in the QD (or pipe-to-barb) at the stat, and you didn't have the restriction in the tee's, could you flow enough coolant to make it difficult to warm things up from a severe cold start? Another thought as to why they may have orifice supply and return for the rear heat... perhaps part commonality, to avoid assembly error?
 
NoDak said:
I confirmed with gm parts book that the supply and return "tee" fittings are identical p/n's. Thus, the orifice part of the "tee" is at position #3 and #6 restricting flow to and from the rear heater. I forgot to measure the size of the orifice in the plastic tee. However, the orifice in the QD is approximately 0.260" diameter.
Click to expand...

I also confirmed the tee's have a 13/64" (.203") diameter orifice to restrict flow "to" and "from" the rear heater.

I guess someone should put this information in the library somewhere???
 
NoDak,

On my friend's 1997 K1500 Suburban, the restriction for the heater system is not in the T's. It is in the quick connect fitting in the dual thermostat housing. The Tees were the same. I have not measured the actual line size to the rear heat exchanger, but the lines at the back of the motor (the last rubber connectors with 90 degree els in them) are both 3/4". The front heat exchanger has one 5/8" and one 3/4" connection. (surprisingly the factory diagram shows the smaller line into the front heat exchanger as the "outlet")

Just looked at a factory breakdown. The "quick connect" actually has this description:VALVE,HTR WAT FLOW CONT(INCLS 5)(5/8 FLOW CONTROL)(NO-FLOW WASHER)(8.846)

Hope that helps,

Hag
 
Well, here I am again with the rear heat problem returned! Cold weather has rolled in. In normal driving around, the air coming out of the rear vents never gets above "cool" (I know, real scientific, huh?). I played around a little bit today and drove awhile with the radiator cap (coolant overflow) off - thinking that if there was still an air bubble, that might help it work it's way out. No dice.

So, while in the driveway, I flicked both "high idle" switches (about 1600RPM) and let it there for a few minutes. The rear vents started blowing warm (not as hot as the front gets) air. Then, I flicked back down to normal idle and the rear vents gradually went back to only cool air.

Why can't this just work!!!!

In regards to a restriction being at the t-stat housing... how can that functionally control which direction (rear or front) the coolant flows? One of the things that I had changed (while the engine was out) was that quick connect fitting, but I don't understand how this would affect anything since it's "upstream" of where the diversion to the rear and front cores is?

So, even though my T's are exactly the same (same ones that have always been there) as each other, maybe something came loose from one? BUT, it appears some of you have restrictions in the T at the rear leg of the T? Am I wrong, or does that seem counterintuitive to solving my problem?

Yours truly,
Still grasping.
 
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One cannot forget to check the basics... is it possible that a heater tube got pinched during engine swap or other activity? Might be worth tracking the hoses (kinked?) and tubelines (smashed?) from front to back, just to rule out a possible restricition? I'd also take apart the tees to make sure something did not fall into the orifice?
 
Absolutely,

Climb underneath and feel the lines. Since you had "some" heat, it has to be a flow problem. (Ok, possibly not, if you were in defrost where the AC compressor was operating, it could be a blend door, but since you didn't notice it "freezing cold" before you high idled, I would take that argument out)

you should feel the "hot" line (supply) if it is hot until a point BEFORE the rear heatexchanger, voila, your plugging is there.
If it feels pretty hot all the way until it turns into the rear heat exchanger, BUT cold on the return line, the Heat exchanger is probably restricted.
If it feels hot to the exchanger and hot from the exchanger, keep feeling, it should hit a cold point. voila restriction is there.

My $0.02 on the restrictions.... in the '97 the restriction was in the quick connect. So, both front and rear heat exchangers would have theoretically been flow reduced equally. Well, when you have two free ranging heat exchangers on common supply and common return lines, the heat exchanger with the least total resistance will see a higher portion of the flow. (you have uncontrollably supplied 2 independent systems simultaneously. They will automatically balance to each other, but flow 1 x pressure drop 1 will equal flow 2 x pressure drop 2).

Ferminator and Nodak are right look for a pinched/blocked line.

you could also disconnect the rear heat (inlet and return at the firewall) and connect each one independently to a hose the water should flow through pretty easily. (It may flow more quickly one way than another, indicating a hose failing internally. You could quickly use that to your advantage and connect that end to the supply side of the heater circuit until you can repair it)

Good luck,

Hag
 
I have checked the lines from the engine all the way to the rear core - I can confirm that nothing is pinched.

I will feel the supply line and the return line this weekend (near the rear core) for temperature.

When I had flushed everything (a little while ago), I flushed it both ways and got very little sediment coming out (it seemed pretty clean). I also flushed it by "gravity" to check how easy fluid flows through. I did this by simply inserting a long funnel into the lines (after taking them off the rear of the "T's") and pouring fluid into the funnel. As fast as I could pour it in, fluid came out the other line. I think that means no restrictions? Not sure, though.

EDIT: I'm still confused about this "restrictors in the T's" thing. It seems some have them (and the heat works fine). It also seems that some don't have them (and the heat works fine). I am 100% sure my T's don't currently have them. And, if the restrictors are in the part of the T that goes to the rear core, wouldn't that make my problem worse? I don't discount anyone that has the restrictors, I just don't see how it would help in my case?

Oh, I have tried local dealers, but I can't seem to find anyone there that has enough background knowledge on this subject.
 
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