1978 Eldo Pesky Fogging Problem

[Jakes]

Lately, after starting the car in the garage (and letting it warm for 10 min. to overcome cold engine bog/sag -- my earlier posts on this subject), the windshield starts to fog up above the defroster vents and gradually extends to the door and rear windows.  Operating the defrosters doesn't help much and I have to wipe away the fog which doesn't clear away as "cleanly" as when you wipe away moisture condensation.  When I set out from the garage the fogging starts all over again.  Even after thoroughly cleaning all the window surfaces the problem still occurs.

HVAC works fine, the floor and HVAC ass'y under the dash are dry, there's no fumes or odor, the inside air feels normal and nothing's leaking under the hood.  The coolant level in the overflow jug seems normal, but from time to time I add to it to account for what I believe is gradual evaporation.

What's going on?     The blower pushes a low flow of air from the floor vents with the switch off which is what it's designed to do.  I'm suspecting a "weeping" of either coolant or refrigerant from the heater core in the form of invisible, odorless vapor that's blending with the low blower air, condensing on the cold window surfaces and won't clear with the usual ventilation.  A test might be to remove the blower fuse and see what happens.  Your advice, as always, is appreciated.

[Cadman-iac]

Hi Paul,

It sounds like you have a heater core going out. Can you smell a sweet odor coming out of the vents?
I had that problem with my truck years ago, and didn't realize what it was,  until one cold day when I needed the defroster, and it blew antifreeze all over the windshield. And that stuff is a real pain to clean up. It gets into all the duct work and you almost have to remove it all and flush it out with water.
But the telltale is the odor, check for that.

Rick

["Cadillac Kid" Greg Surfas 15364]

It sounds like you are the recipient of the frequently occurring heater core gift.  If you are adding coolant it seems to be going somewhere. If there are no other leaks then I would strongly suspect the heater core.  After I did the last one I talked to a local mechanic about how much he would charge to do the work and he estimated about $800.00.  Next one that has to be done will be done by him. Enough said. The Factory Service Manual has an excellent section on heater core replacement, and following it step by step IS the most efficient way to do the job.  Shortcuts tend to take you places you really did not want to go.
Greg Surfas

[fishnjim]

Yes, usually you can smell it(sweet odor) before you see it.   Check under the front carpets along the fire wall for wet spots.
I wouldn't let it sit like that, it's the #1 cause of floor pan rot.

[79 Eldorado]

I would agree with the assessment it's likely the heater core but one other thing, which would cause window fogging, is if you have no outside air bleed. A defroster must always have some outside air else you will fog your windows. While in defrost mode all GM cars are set-up to have some outside air even if you can control the recirc vs outside air. It's that way specifically to avoid fogging.

As people mentioned coolant smells sweet. Once you know the smell you will never miss it. If it's really odorless then it's not coolant but as others mentioned it is likely coolant. If it's coolant it's often more difficult to get all the film/ residue off the window.

Scott

[Jakes]

I had a feeling you'd agree that the heater core is the culprit.  But there's absolutely no telltale (sweet) coolant odor  even when I put the switch on "Economy" which directs the air from the dash vents.  (I was COVID positive a couple of months ago...OK now...and lost my sense of taste/smell which has mostly come back, but maybe not enough to sense the coolant odor.)  As for topping off the overflow jug I vary rarely do it because the level stays an inch or two above the fill mark.  I guess I should run the engine a couple of times and see if the level depletes faster than I thought.  Also, good idea to carefully check under the carpets for wetness.

What do you think about my idea of pulling the blower fuse and running the engine to see what happens?  If the windows stay clear that'll probably confirm a leaky heater core.  I have the 77-78 shop manuals but at my age I'm not about to attempt the R/R.  My ace mechanic will probably appreciate being able to refer to them.  The last time all the windows fogged up like this was when I was a teenager and.....well....you know!

As for the defrosters, the air flow is not as strong as one would expect.  Strangely, the air flow force will change with a change in the temperature setting.  I'd imagine any problem is likely related to infrequent selection of this mode which might have affected the smooth mechanical operation of the various deflector doors within the HVAC box. For all intents and purposes I never use the defrosters, but I've never had this fogging issue.   

[Eric DeVirgilis CLC# 8621]

OP already mentioned difficulty in removing the contamination from the glass and coolant level dropping, in addition to steam out the vents.

Looks like a duck, walks like a duck, quacks like a duck...it's a duck. 

[Eric DeVirgilis CLC# 8621]

I had a feeling you'd agree that the heater core is the culprit.  But there's absolutely no telltale (sweet) coolant odor  even when I put the switch on "Economy" which directs the air from the dash vents.

For whatever reason you're simply unable to smell it.

What do you think about my idea of pulling the blower fuse and running the engine to see what happens?

Waste of time. Leaking heater core isn't electrical related.

As for the defrosters, the air flow is not as strong as one would expect.  Strangely, the air flow force will change with a change in the temperature setting. 

Defroster setting ONLY sets blower to fixed high speed and bypasses the coolant warmup sensor. All other settings, the blower is designed not to come on until the coolant has reached a certain temperature. 

Blower is supposed to vary according to how much heating/cooling is needed based on the temperature setting on the Climate Control panel and the temperature of the interior. Blower speed affected by changes in temp setting 100% normal. However this should not occur with the defroster setting which is high fan speed only.

None of this has any bearing on the heater core which is definitely bad.

[35-709]

Does sound like a heater core, BUT, before starting out on a project like that, one more thing to check, be sure your A/C drain is open and water created by the A/C system is able to drain out of the box.

[Jakes]

Valuable advice...THANK YOU gentlemen.

Check under the front carpets along the fire wall for wet spots.

Guess what.... I crunched down under the dash (oh, my aching back), jammed my fingers between the top edge of the carpet and the fire wall and it felt damp, including the insulation.  Not wet, no moisture spots, no liquid wetness on the fingers but a definite "clamminess" all along the area below the heater core.  So even though I can't sense that sweet smell, it's possible that the leak is small enough to cause the fogging problem but not enough to require frequent filling of the overflow jug.

What do you think about my idea of pulling the blower fuse and running the engine to see what happens?  If the windows stay clear that'll probably confirm a leaky heater core.

Waste of time. Leaking heater core isn't electrical related.

I realize that.  My theory was that assuming the low blower air flow from the vents under the dash is "pushing" the coolant vapor toward the windows while the engine's running, there would be little or no fogging if I stopped the blower by removing its fuse....which would confirm the heater core problem.


As for the lack of coolant smell...go figure.  I smelled my "clammy" fingers (...that sounds so bad) and even poured a small amount of my Peak 50/50 "old car" green coolant into a cup, tried to detect that telltale sweet odor even on my fingers and...nada.  Lingering sensory effect after COVID recovery?...who knows?

Sounds like I'm off to see my wizard mechanic.  Many thanks again.

[J. Skelly]

not an easy job to replace the heater core on one of these; I ended up having the Cadillac dealer do it on my '77

[79 Eldorado]

Does sound like a heater core, BUT, before starting out on a project like that, one more thing to check, be sure your A/C drain is open and water created by the A/C system is able to drain out of the box.

Paul,
It seems like a duck but this comment is certainly valid and a pretty easy check. Every HVAC module has a drain for the evaporator condensate (water which forms on the evaporator) to drain to the ground. It's just plain water. If the drain is clogged the case will start to fill and you could get water in the interior and you could pick-up more moisture with the airflow.

If the airflow seems poor I also wonder if doors are not moving to the proper positions and if the outside air valve, which should be located in the cowl, may be stuck in a closed position.

You need to look under the car for the HVAC drain. It should be something like a 1/2" tube exiting your AC "Box"; the under hood box. Normally they will have a soft material hose pushed over the drain.

For the second item I'm not certain how your outside air valve is actuated but if you can duplicate the actuation with the car off and someone listening near the top of the cowl maybe they could hear it. It should be on the passenger side.

If it's neither one of those items I think what you've got is what we commonly refer to as a "duck"

Scott
PS: When I was writing the prior reply I was thinking if it's coolant and you cannot smell it it's time for a Covid-19 test. Crazy. Hope you won't have any lingering symptoms.

[hornetball]

Simple enough to bypass the heater core until you decide to get it fixed.  The hoses are accessible at the firewall.  That would also be a definitive test as to whether it is the heater core causing the issue (most likely) or something else.

It's strange that you aren't smelling coolant.  I usually smell coolant long before windows fog.  The smell is strong.  When you touched the carpet dampness, did your fingers smell like coolant?

[76eldo]

They make a plastic fitting that it for jumping out the heater core which is basically a plastic tube with barbed ends. One side accepts the 5/8 hose and the other side accepts the 3/4 hose.
Since you may need to do this someday on the road everyone should have one in their toolbox that they take on road trips along with a couple of hose clamps.

[Cadman-iac]

Paul,

Another telltale sign that it's antifreeze and not just the condensate from the evaporator, is how it feels on your fingers. The antifreeze will leave a slippery film, kinda sticky. If it only feels wet, then it's probably just a plugged drain.

Rick

[Eric DeVirgilis CLC# 8621]

...and the fact he's adding coolant...

[Jakes]

Another telltale sign that it's antifreeze and not just the condensate from the evaporator, is how it feels on your fingers. The antifreeze will leave a slippery film, kinda sticky. If it only feels wet, then it's probably just a plugged drain.

Hard to tell.  The carpet definitely feels moist, but not enough for my fingers to feel slippery or sticky.

They make a plastic fitting that it for jumping out the heater core which is basically a plastic tube with barbed ends. One side accepts the 5/8 hose and the other side accepts the 3/4 hose.

Simple enough to bypass the heater core until you decide to get it fixed.  The hoses are accessible at the firewall.  That would also be a definitive test as to whether it is the heater core causing the issue (most likely) or something else.

It's strange that you aren't smelling coolant.  I usually smell coolant long before windows fog.  The smell is strong.  When you touched the carpet dampness, did your fingers smell like coolant?

Where do I get such a fitting...any major auto parts store?  And wouldn't I need to get the coolant out of the heater core?  Otherwise it would have to leak out to the point where there's nothing left in the core and the windows won't fog anymore, right?...and given how slow the leak seems to be, that would take a long time.

I simply don't smell any coolant, even from the jug I keep (Peak 50/50).  It's possible that the return of smell from my COVID recovery simply doesn't "include" antifreeze scent.  Guess I'll have to enlist someone to be my "bloodhound" (not my wife who's had sense of smell issues).

Haven't yet had chance to check the A/C drain that was suggested.  I hope that's what it is since my mechanic and others have told me that R/R-ing the heater core is a difficult, time consuming job that risks damage to the dash, air outlets, etc. My guy said he's done it before, but recommended that I talk to a shop called Cap-A-Radiator in Farmingdale, Long Isl. which specializes in HVAC work on classic cars.

Every HVAC module has a drain for the evaporator condensate (water which forms on the evaporator) to drain to the ground. It's just plain water. If the drain is clogged the case will start to fill and you could get water in the interior and you could pick-up more moisture with the airflow.

You need to look under the car for the HVAC drain. It should be something like a 1/2" tube exiting your AC "Box"; the under hood box. Normally they will have a soft material hose pushed over the drain.

If it turns out that it's a clogged A/C drain, can it be cleared without having to dismantle everything?

Thank You, again, gentlemen for your help.

[harvey b]

Anti-freeze has a sweet taste to it,maybe see if you can get your fingers into it some how and lick them,the taste is quite distinctive,ask me how i know .Or maybe have someone who is there to see if they can smell it?. There is also Bars leak,it works in a pinch.Can you take up the carpets to see if the floor is wet,when the carpets are wet that will cause the windows to fog up,but normally not when you drive. Harveyb

[35-709]

"Where do I get such a fitting...any major auto parts store?  And wouldn't I need to get the coolant out of the heater core?  Otherwise it would have to leak out to the point where there's nothing left in the core and the windows won't fog anymore, right?...and given how slow the leak seems to be, that would take a long time."

Yes, an auto parts store, tell them what you are trying to do and the size you need.  When you disconnect the heater hoses to join them together the coolant will drain out of the heater core so no more coolant to leak, plus the heater core will no longer be subject to cooling system pressure.  The hoses may be difficult to remove as they often get stuck to the heater core nipples.  Take the clamps off and, if stuck tight, use a pair of pliers on the hose over the nipples to rotate it back and forth break them loose, they should come off relatively easily after that.  If not, feel for the end of the nipples and just cut the hoses off there.  Be sure to loosen the radiator cap (when cold) to release any residual system pressure, hold the hoses up above the radiator coolant level or you will lose coolant from the system and have a mess.  There will already be coolant draining from the heater core so you might want to be ready for that.  An extra pair of hands might be nice to have. 
This all assumes that you have first checked the condensate drain from the evaporator, you can often free up any blockage with a straightened coat hanger wire or similar pushed up through the drain from the outside, or a quick/short blast from an air hose.  No matter what the source of water, the carpet should come out or at least be folded back so that it can thoroughly dry or you are inviting rust holes in your floor. 

[79 Eldorado]

Paul,
For the AC drain yes you can likely clear it without any disassembly. Sometimes leaves, rodent nest material or even a spider may have built a nest in the tube. You can insert something and try to clear it. You can adapt something to use a shop vacuum to suck it out.

For the coolant. I wouldn't try to taste it. If you can get your fingers wet with it simply rub them together. If it's coolant they will get a little sticky as it dries. If you want to know the feeling exactly use a paper towel or rag and wick some coolant from the overflow bottle onto the rag and touch it with your fingers.

For clearing the heater core: Once you remove one of the hoses you can apply light air pressure and blow it through the heater and out the other hose. If there is back pressure it may want to blast back at you so you need to be careful. You could always take the opportunity to change your hoses and then just leave the second side connected to the heater; remove the next connection and then blow the coolant into a pail with the second hose keeping things from getting messy.

Another option is a vacuum, like a shop vac, but you may want to "craft" your own catch can for the shop vac if you are like me and don't like using your wet/dry vac for wet. Think of the catch can which comes with a Mightyvac. I've used an empty sauce jar. What ever you use it needs to have some structure; at least enough to withstand the vacuum reasonably.

I've done the 1979 but your '78 was the prior body style so I don't know if they were the same. The '79 requires removal of the entire dash, A-pillar to A-pillar, and I'm not just referring to the gauges. I was able to get mine far enough away from the firewall that I didn't really need to disconnect any wiring that I can recall. I've removed '79 dashes at least 4 times now though.

One tip is get a cardboard sheet or box lid and label/stick each fastener you remove through a hole in the cardboard so you know where everything goes.

Scott