Suburban Rear Heat Not Working

[DennisG01]

The rear heater in my Burb has been not working for about a year. But, as I don't sit in the rear, I haven't been too worried about it. But, I'd like to get it going again. I read through Chilton's, but that does not seem to have the answers I'm looking for. I also searched here, but was still unsuccessful.

Here's what I know:

-- The front works fine.
-- There is no difference if I control it from the front or from the rear controls.
-- The rear blower works fine. But, is this odd?: The air coming out of the rear vents is a little bit stronger when the temperature dial (front controls or rear) is set on cold as compared to hot.

Here's what I've done:

-- Flushed the rear core from the engine bay. I flushed "backwards", meaning I attached a garden hose to the return line that goes to the radiator (top, starboard side). I extended the hose that normally comes from the T-stat housing into a bucket.

At first, I could tell there was some resistance and about a tablespoon or so of crap came out. After a minute or two, the water was running out of that extended discharge hose as fast and clear as it was coming in.

-- I also flushed the front core while I was at it. That one was pretty much clear right away.

I am assuming the problem lies somewhere back in the right rear quarter panel trim. Maybe some type of "diverter" or something? But, then again, the air flow does change in intensity when I move the temperature dial from cold to hot.

But, I'd like to hear from you guys if I'm on the right track, how I should proceed and what specifically am I looking for?

Also, it looks like I have to take a bunch of extra trim pieces off to get that interior quarter panel piece off. Is that right? Any tips?

Could it be as easy as a fuse? I can't find any that is specific to this problem, nor do I see any that are blown (unless I missed something). The only fuse that I have permanently removed is the one that controls the DRL's.

 

[Chevylover]

Hi Dennis !

HOW does the intensity change while going from hot to cold ? From hot to cold it is normal, if the intensity raises a bit.

Sounds to me, that there is some air (bubble) in the system so the heat could not reach the rear core.

Only a shot from the hips, cauz I got no Sub, but perhaps it helps.



Cu,
Sven

 

[Rodd]

I had a similar problem except mine was opposite. Front was always cold (once in a while it would get luke warm). What cleared it up was when I replaced my h2o pump. Before I took it off I put the hose in radiator fill and connected the return line into a bucket. Started the truck and turned both front and back heaters on high (I dumped the crap in my raw sewage line, it took about 5 - 5 gallon bucket fulls). Then I replaced h2o pump. I then filled up w/ approximately 3 gallons of 100% coolant w/ truck running and both heaters on. Obviously you don't need to replace the h2o pump.

 

[Missy Good Wench]

Check to make sure that you are getting hot water through the rear core.

If there is hot water to the core then its got to be an air issue, as in the blend air door is not operating correctly.

If you are getting air from the vents it's likely not a fuse.
The rear system works much the same as the front unit with a little servo motor to control the blend air door.

Many times these fail simply because they dont get used enough and the motors fail to opperate the door.


Take the panels off and get at the guts of it and then diagnose what is and isn't working.

Missy

 

[DennisG01]

Sven, I would say the intensity may go up about 15% going from hot to cold. Just a guess, though. It's a noticeable change, but only slightly.

So, I gotta tear into the rear quarter, huh?

The only procedure that is outlined in the Chilton's manual, in getting to the rear core is "remove inner fender" and "remove interior trim". Not much in the way of an explanation. That's fine, I guess I can't expect a $30 book to go into great depth on every little thing.

I guess I gotta just start removing trim until that large, rear quarter piece comes out???

I will start the truck up and put the rear heat on high for a bit - and see if the return line gets warm to the touch.


Rodd - so a flush did it for you?

 

[Rodd]

Rodd - so a flush did it for you?

Yes in conjunction w/ swapping out my leaky h2o pump. However I don't think that the leaky pump was causing my problem because the lack of heat started a year before the leaky h2o pump did.

 

[DennisG01]

Yes in conjunction w/ swapping out my leaky h2o pump. However I don't think that the leaky pump was causing my problem because the lack of heat started a year before the leaky h2o pump did.

OK. Thanks. I was really (really, really, really...:rolleyes5 hoping that the flush would have solved my problem. Oh well. I guess now I get to learn more about how to remove that rear quarter.:smile5:


I'm curious why the change in air flow intensity out of the vents when going from hot to cold on the temp dial????

 

[DennisG01]

Ran the engine for a good 25 minutes with the high-idle at 1,000rpms.

The return line (from the rear core) in the engine compartment got a little bit warm (about 90*), but I started to suspect that was just heat transfer (both from engine and the front core).

So, I crawled underneath near the right rear tire, and sure enough... the supply line was getting good and warm, but the return was still barely higher than the ambient temp.

Now I'm confused... After flushing it last week, the water was flowing very nicely through the rear core. Now it appears it is not flowing through it.

Am I missing something? What's going on? I don't get it.

 

[Rodd]

Ran the engine for a good 25 minutes with the high-idle at 1,000rpms.

The return line (from the rear core) in the engine compartment got a little bit warm (about 90*), but I started to suspect that was just heat transfer (both from engine and the front core).

So, I crawled underneath near the right rear tire, and sure enough... the supply line was getting good and warm, but the return was still barely higher than the ambient temp.

Now I'm confused... After flushing it last week, the water was flowing very nicely through the rear core. Now it appears it is not flowing through it.

Am I missing something? What's going on? I don't get it.

It could have an obstruction. Something could have broken off and be partially clogging it.

 

[dangerousdave]

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

On my wife's burb, she never used the heater,(south Texas) and it rotted through.

Getting at the air door and core is a PITA.
If I had to do it over again, I'd start fresh Saturday am, drink only water, juice, tea, and coffee; be happy if you're done by sunday pm.

Then celebrate.:cheers2:

Just my $2.50, for inflation.

 

[Chevylover]

So, I crawled underneath near the right rear tire, and sure enough... the supply line was getting good and warm, but the return was still barely higher than the ambient temp.

Now I'm confused... After flushing it last week, the water was flowing very nicely through the rear core. Now it appears it is not flowing through it.

Am I missing something? What's going on? I don't get it.

So there will be the problem. Now there could be an AIR bubble in the core after you flushed it or you loosend some crap while flushing which now this is blocking the line. First, I would check/try to get the air out. If there is no more air in and it still don't heats, you'll know, that (I would guess) the return line or the core itself is blocked.


Cu,
Sven

 

[knkreb]

Something else to check is if there is a valve to the rear core... The bus used to have a vacuum operated valve for the rear heater... which I don't think was a GM OEM offering... but a thought. It was also a vacuum operated HVAC system in the front. But as said... it should be a servo operation so that you have rear and forward control.

Followed the lines?

 

[DennisG01]

So, I should wait on looking into the diverter and go after the air bubble, first?

So, open the bleed screw on the t-stat housing with the engine running, correct? For how long? Until air no longer comes out? I assume I should keep an eye on the overflow tank.

Does idling the engine with the overflow tank's cap removed accomplish anything?

By the way, I have driven the truck and engine temps are normal.

 

[DennisG01]

Thought of something else. If I use the bleed screw on the T-stat, that doesn't necessarily mean the air will bleed out of the rear core line, right? I mean, that's a secondary system so if it's got an air bubble in it, it very well could stay in it.

Am I thinking about this correctly?

Should I then just disconnect the supply and return lines at the "T" in the engine bay and physically pour AF through the supply hose until good flow comes out of the return (keeping the supply hose higher than the return)?

 

[guybb3]

I don't think it's an air bubble. I'll bet it's a restriction.

 

[dangerousdave]

chunk-o-crap fallen off the inside of a corroded metal line, maybe?

 

[DennisG01]

chunk-o-crap fallen off the inside of a corroded metal line, maybe?

I was hoping for an air bubble or a something else I could flush out. No luck. I just hooked up a manual hand-pump and pushed AF very easily through the rear core both backwards and forwards. I did this from the hoses up in the engine bay. Basically, this is my second time flushing it.

I opened the bleed screw a few times and very little air came out. The level in the overflow tank is good. Squeezing the upper radiator hose resulted in both AF coming out the bleed screw (more forcefully) and I could see the level in the overflow tank change.

I guess what's confusing me a little is I don't completely understand how the core operates in regards to hot/warm/cool air. Is there some type of valve in the inlet side of the core that opens and closes in relation to the temperature switch? Is that the "diverter" that was mentioned above - the one where I have to rip into the rear quarter?

Does anyone happen to have a picture or, better yet, a schematic of a heater core and this "diverter"? That would help me visualize how this works.

I don't think it's an air bubble. I'll bet it's a restriction.

What type of restriction are you thinking of?


Are these things always this difficult?

 

[Missy Good Wench]

The heater return has a free flow to the radiator RH tank. There is almost no way it could be airlocked.

Is there a control valve that stops water flow through the core or from returning to the front.

The older Burbs that had rear heat had a control valve to stop the water flow though the core to keep the core cool when the heat was turned off.

Snoop around under the hood and see if there is any sort of return line control that could be inoperative?? There could also be a valve in the rear heater case too that controls water flow.

Missy

 

[DennisG01]

The heater return has a free flow to the radiator RH tank. There is almost no way it could be airlocked.

Is there a control valve that stops water flow through the core or from returning to the front.

The older Burbs that had rear heat had a control valve to stop the water flow though the core to keep the core cool when the heat was turned off.

Snoop around under the hood and see if there is any sort of return line control that could be inoperative?? There could also be a valve in the rear heater case too that controls water flow.

Missy

OK. So follow the lines back (KNKREB: Now I understand what you were saying) looking for a device. I'm positive there is no valve in the engine bay.

Short of coming across the device inline with the hoses (which would be a VERY nice surprise), next step is to get into the rear quarter, right?

Would this device basically be functioning as a bypass? And it might be stuck in the bypass position so that the AF isn't actually flowing through the core?

Sorry for all the questions - I'm really just trying to fully understand how the system operates.

 

[Chevylover]

Don't know if it helps, but here some pics, part# and I can't see no valve or similar in the system.

http://www.compnine.com/index.php?u...puid=1&modelid=6923&majorgroup=08&grouptype=B

http://www.compnine.com/index.php?u...puid=1&modelid=6923&majorgroup=08&grouptype=B

http://www.compnine.com/index.php?u...puid=1&modelid=6923&majorgroup=08&grouptype=B

Cu,
Sven