Hello,
I've got a 1972 corvette SBC without AC equipped, and I am always getting hot air coming to the defrost vent. When the engine gets up to temp it ends up steaming up the windshield, and it's annoying to keep wiping the interior windshield every 5 minutes...arguably kind of dangerous. Even with the windows down the windshield fogs up.
This seems weird to me, because in other newer cars I've been in it doesn't really fog the window. Even when it is hot out and the defrost is activated, it just blows hot air, but doesn't fog the windshield.

Could this fogging be caused by air being made "dirty" as it comes in through the system?
Has anyone else experienced this?

It seems like there is a vacuum leak somewhere in the vent selector, which i will have to track down. For whatever reason, the heat control also doesn't seem to work.
I live in CA, so I'm rarely in need of any heat, so I am looking for a temporary solution. (Not to mention i just got done getting all the gauges to work again and reassembled the dash.)
I know the temperature control isn't vacuum actuated, and is just a cable.
I imagine this cable goes to the heater box in the engine compartment, and maybe i could just reach in there an turn the lever controlled by the cable, closing the heater box flap.
I see a few diagrams of how this is routed, but I can't see where it connects to the heater box.

Is this possible?
Any chance someone has some pics of where the cable connects to the heater box flap?

 

Hate to be the barer of bad news but, it sounds like you have a heater core going south. Moisture on the inside of the windshield is a sure sign.
You may want to add a manual shut-off valve on one of the heater hoses as well due to the region you live in. NAPA has one that allows complete closing or just a trickle of coolant passage.

Don't know about the control cable. I have the leaky, cheap, plastic, vacuum system, if you want to trade.

 

A temporary solution would be to loop the heater hoses back on themselves. If they are old enough to be worth replacing anyway, you can get a 5/8" to 3/4" inch adaptor and some hose-clamps at NAPA and cut the hoses. This will help keep you cool in the summer, too, but be careful, as the plastic adapter can crack after a few years.

There are better, long-term solutions involving valves and whatnot (search here on the forum). It looks like the correct, not-easy-to-implement solution is for you to replace your heater core. It's leaking. Check the carpet for moisture, too.

Best of luck!

 

Well shoot!
This really helps me narrow down my options. Thanks!

Does this mean coolant is leaking from the core, and is getting blown on my interior windshield?

I'd imagine this would cause the coolant level to run low?
Roughly how much coolant can i expect to leak over a given period of time?
Do i need to fix this right away before driving it again?

 

Either by-pass or fix it soon.

The heater core chamber will hold a little puddle of coolant in the bottom. May not even drip on the carpet. But as the blower fan moves warm air over the puddle its gathers that like "lake effect" and not so nicely deposits the sticky, stinky anti-freeze on the glass.

But! Good news! You do not have A/C which should make core removal easier.
Caution. Double check with other members which core fits, works and looks exactly like the original. Evidently, a lot of junk for sale out there that does not fit correctly or leaks shortly there after.

 

Hi m,

"I'd imagine this would cause the coolant level to run low?
Roughly how much coolant can i expect to leak over a given period of time?"

It will take very little leaking coolant for your windshield to fog up. Even if the leak is just a 'seep' at this point that will be enough.

You should however be able with the use of the heater/defroster controller on the shifter console be able to shut off the supply of air to the defroster duct which is blowing on the windshield.

Is the controller operating?
The right side wheel controls the temperature. You should have yours rotated to the cold 'C' setting which closes the door so the air flow by-passes the heater core in the air box.
The left side wheel should be set to 'Off'. This will minimize the effect of the leak until you have an opportunity to determine what's going on with the heater core.

This is something you should repair soon because if the leak increases it could begin to drip/run on to your passenger's side front carpet.

Good Luck!
Regards,
Alan

Happy Thanksgiving!

 

The cable on the control head does not control the air to the defroster.....what it does is when you turn the wheel to defroster .....on the left side of your control head there is a vacuum switch that will route the vacuum to the vacuum pod that is attached to your heater box that will either direct the air to the floor...or the windshield...or neither.

IF you are not getting that vacuum pod to move that door....you will need to replace that pod and that is IF you can verify that you do have vacuum going to the vacuum switch.

The reason that you MUST have vacuum going to that vacuum switch is because the flapper door for your floor air vent or defroster is neutrally balanced. So if you have no vacuum...air will go to the windshield and also the floor.

So having the left side roller wheel set to OFF will do nothing to help out your situation...because that will put that flapper door in the neutral position ( due to no vacuum going to it)....which will still allow air to get to your windshield.

GM did this as a default mode...so if you lost vacuum..and live where it gets cold and icy...you will always have heat go to floor and windshield for defrosting.

I will starting thread about the actual vacuum pod for a non-A/C car that controls the defroster and floor air distribution...because I have found issues with the new ones being sold and want to let people know about it....so..I literally have been through this not too long ago.

DUB

 

Looking forward to your thread on this. As you know, we took ours out and found lots of PO issues that had been poorly addressed.

Curious to see how It all goes back together properly.

 

I will get to it as soon as possible...I am super busy at the shop right now and when I get home....I am wiped out. And oddly enough the forum is how I wind down.

It wont be too long.

DUB

 

[QUOTE=Alan 71;1596027833]Hi m,


Is the controller operating?
The right side wheel controls the temperature. You should have yours rotated to the cold 'C' setting which closes the door so the air flow by-passes the heater core in the air box.
The left side wheel should be set to 'Off'. This will minimize the effect of the leak until you have an opportunity to determine what's going on with the heater core.

This is something you should repair soon because if the leak increases it could begin to drip/run on to your passenger's side front carpet.


Unfortunately, my heat controller doesn't seem to be working on the vent selector wheel or the air temperature wheel, which seems weird, because i would have thought the right temperature wheel would be more reliable with it being an actual cable, and not vacuum controlled.
I guess I just need to trace the cable going to the heater box and make sure the cable moves freely and the flap isn't trashed.
Repairing the vent selector is going to be a bitch, tracing all the lines, but i suppose thats what needs to be done.

Right now, I installed the manual ball valve to stop coolant from going to the heater core. It seems like the air has significantly cooled down. Do I need to install another valve on the outlet side of the heater core to completely stop the leak?

 

This is exactly what happened. I get air to the floor and the windshield. i'm not sure if im getting vacuum to the controller, but I will be tracking this down next.

 

I checked out some videos on how to install the heater core, and it doesn't seem too tough. I did a brief search on the cost of the part, less than $75, which shouldn't be too bad.
I'm curious what you mean about difficulty selecting the right heater core. I know there are 2 different heater cores, one for A/C equipped, and one without AC. I see several companies offering the non-A/C heater cores for relatively pretty cheap. With this being pretty hidden, I'm not as concerned about it looking 100% stock with the patina of the metal or whatever; as long as it fits and functions.

Anything I should be looking for when I buy the heater core?

Can you see anything wrong with this one?:
https://www.stockwiseauto.com/spectr...xf257703f2120&

 

YES...do not be surprised if your cable to the hot/cold door is binding. At take all precautions that you do not break it at the heater box or control head. I have had to take many off in the past and work a penetrating oil down inside the housing of the cable to free it up. Getting penetrating oil inside the housing is quite simple....use gravity and some modeling clay to create a reservoir that you can pour your penetrating oil in and let gravity do its job...along with carefully moving the cable up and down and not splashing the oil on you when doing so.

I am not a fan of an aluminum heater cores....which that one looks like...because it surely does not look like a copper/brass one.

I know the heater cores of today are aluminum....but I still prefer to put back in what it came with....and YES...I know that I install aluminum radiators...so go figure why I feel this way...it makes no sense...but it is what it is. Expect I can see an aluminum radiator if it is leaking but I can not an aluminum heater core.

You may find that even though the heater core looks correct in a photo on a website...when you get it an go to install it...it is off.

DUB

 

Basically, non of the repo heater cores fit correctly.

(If you found one, post it).

 

I might have to do that. The last one I did...the core fit perfectly....but the only hiccup was the slide on tension clip that goes between the two tubes was off a frog hair and needed slight modification.

DUB