Heater off But Heat Sneaking Through Bottom Vent.. Lil help.

[jb3t]

78 C10 here.... It was a nice, warm spring evening and I'm taking a cruise in the ole c10 when I noticed a little heat coming out the bottom center vent. Not much but enough to warm the cabin. Any clue how to fix this? Are there seals on the vent door?

Before you ask... Heat was off, temp on cold.

[tucsonjwt]

I had a similar problem with my two 454 squares. You could have some worn out foam seals on your duct work.

I "fixed" mine by installing a PEX 3/4" shut off valve on the incoming line to the heater so the heater core had no hot water flowing to it in the summer. You can get an automotive valve designed for this purpose but the one I got leaked, so I used a PEX valve - no leaks and turns much easier.

Where I used to work all of the fleet trucks had this done to them since you need all the help you can get in 110 + degree summer heat.

Don't forget to turn the valve back on during the winter or you will be scratching your head like I was when you had no heat.

[Gregski]

hmm now I gotta check mine too

[TexasJeff]

I have the same problem with my 80 model, I just loop the heater hoses together for the summer months, but I am going to look into the PEX valve that "tucsonjwt" talks about that seems like a much easier solution.

[tucsonjwt]

The PEX valve is preferred because it is brass and has "barbed" ends (for lack of a better term) so the ends slip into the heater hose with a nice tight fit - add radiator clamps and you are done.


Watts PEX LFP-560 In-Line Full Port Ball Valve...

[jb3t]

Awesome. Mom going to do it.

Side question... Any fix for the seals on the vent? I've yet to rip it apart and take a look

[motornut]

Something else,some trucks are wired with the lowest fan speed always on.
I had to cut my brown at the switch to have " off".
Check too I've seen a type of the def/floor valve,inside the air box, the rod hookup there is adjustable (3 holes)to always leave air flow up or down, center all up/ all down.

[jb3t]

Originally Posted by tucsonjwt

The PEX valve is preferred because it is brass and has "barbed" ends (for lack of a better term) so the ends slip into the heater hose with a nice tight fit - add radiator clamps and you are done.


Watts PEX LFP-560 In-Line Full Port Ball Valve 1/2-Inch Barb x 1/2-Inch Barb Low-Lead, Brass - Faucet Valves - Amazon.com

Just out of curiosity, what line do you put it on? As there's no bypass line, is there any issue with stopping flow?

[nonstop]

Another thing you can do..... Vacuum operated shut off - some cars use them for A/C. Not sure how to tap it into existing vacuum switch, but you could also wire up a toggle to an vacuum solenoid - sounds complicated but it's not. Just need to scrounge junkyard. Around here, there are some summer mornings that are cold and winter days that are warm. No real solid seasons, so an under hood valve might be a pain!

[Gregski]

Originally Posted by jb3t

Just out of curiosity, what line do you put it on? As there's no bypass line, is there any issue with stopping flow?

man that pic was giving me vertigo

[tucsonjwt]

Valve is on the 5/8" line - the lower of the two lines at the heater box. And correction - it was a 3/4" PEX valve.

I have experienced no heating or cooling problems with this set up.

[motornut]

Originally Posted by nonstop

Another thing you can do..... Vacuum operated shut off - some cars use them for A/C. Not sure how to tap it into existing vacuum switch, but you could also wire up a toggle to an vacuum solenoid - sounds complicated but it's not. Just need to scrounge junkyard. Around here, there are some summer mornings that are cold and winter days that are warm. No real solid seasons, so an under hood valve might be a pain!

My Burbs (88) had a rear combined ceiling AC/heat unit,had a valve under hood, I think to block rear flow.The 87 was separate,don't remember the valve

[rajincajintj]

great advice.

my c30 does the same thing

thanks for the help

[Titomars]

you could go with a vacuum switch at the dash and use a standard vacuum valve in the heater hose line. I used to use a 64 to 66 Thunderbird vac switch for the rear defrost to do all sorts of things on various cars. I mostly used them for powerglide equipped street/strip cars. I used them for switching off and on the vacuum modulator. On street, off race. I might go this route for my own truck.

[Bigstevex4]

The fan runs all the time by law mine does same thing 83 no Ac the duct work is meant to stop air from flowing. through it. but you still have that hot core.
And shutting it off around here is a pain when its 25 in morning and 78 at 5
just heard record low was 25 and high was 92 for yesterday. Any way put a shutoff and choke cable works great.

[Liberty]

Some of our early squarebody trucks had factory vac controlled heat lines that cutoff heat flow when the A/C ran. I saw one in the shop the other day that had this setup.

[Liberty]

Originally Posted by Bigstevex4

The fan runs all the time by law mine does same thing 83 no Ac the duct work is meant to stop air from flowing. through it. but you still have that hot core.
And shutting it off around here is a pain when its 25 in morning and 78 at 5
just heard record low was 25 and high was 92 for yesterday. Any way put a shutoff and choke cable works great. Attachment 1405165

My 82 doesn't run the fan at all with the controls set to off.

[tucsonjwt]

Keith can verify, but I think GM in the 70s came up with the "flow thru ventilation" idea which meant that the fan was always on low for improved ventilation, and possibly safety.

As far as I can tell, the hot coolant always circulates to the heater core, so it has heat- but that heat is not sent through the ductwork, unless the foam on the duct doors is worn out, which it was in all of the 3 squares I have owned.

I don't like vacuum controls because I think there is too much unreliable and potentially leaking vacuum points in these old trucks. I don't know why there are vacuum controls in vehicles when electric/electronic controls are much more predictable and reliable and don't affect other systems when they fail.

I do like the idea of the cable controlled valve for those who have big temperature swings during a single day. Any close up pictures of how that valve operates and where to get one? My concern is that the specialty valves I have used are not sturdy enough and leak over time. Plumbing valves need only about 1/4 turn for on/off (globe valve, not gate valve.)

[motornut]

Originally Posted by Bigstevex4

The fan runs all the time by law mine does same thing 83 no Ac the duct work is meant to stop air from flowing. through it. but you still have that hot core.
And shutting it off around here is a pain when its 25 in morning and 78 at 5
just heard record low was 25 and high was 92 for yesterday. Any way put a shutoff and choke cable works great. Attachment 1405165

Cool,any closer pics,more details?

[Bigstevex4]

That loop in the end is a must to get it to work smooth the shut off takes a wide arc any choke cable the shut off 20 bucks amazon? we used those types shut offs for decades in heavy equipment in 30 yrs. may have replaced 1 or 2.
Matter fact was 36 this morning on way work shut it off at lunch 60 sun shining.

[tucsonjwt]

Maybe like this one.

http://www.oreillyauto.com/site/c/de...0886&ppt=C0108

[nonstop]

Originally Posted by tucsonjwt

Maybe like this one.

http://www.oreillyauto.com/site/c/de...0886&ppt=C0108

Just food for thought here - we have a cable controlled temperature switch now (right?). What about putting one of those valves in the heater line and using the temperature switch (modified) to control the valve?

[greg64]

Originally Posted by nonstop

Just food for thought here - we have a cable controlled temperature switch now (right?). What about putting one of those valves in the heater line and using the temperature switch (modified) to control the valve?

I've had that same thought. Use the existing temp control to modulate the valve, and fix the damper in the heater box so that all the air passes through the heater core, all the time.

[Bigstevex4]

With no hot water in core I turn fan on like vent works great. looked at that orilys link sure that's same one.