vacuum actuated heater shutoff help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Custom 68 · 05-24-2008, 04:51 PM

well ok I hope that title makes sense. Anyway I have got my AC running but have seen a valve that shuts off the hot water to the heater core that uses vacuum to operate.
does anybody have a part number I know they had them on several vehicles?
And how does it work is it just kindof on or off working off the AC switch or does it regulate based off the hot to cold lever? I have my inside to outside vaccum doors working but never had one of these on my original AC truck.
Any help or thoughts if I need one or not would be great.

Thanks
Dave

**clay68c10** · 05-24-2008, 04:58 PM

Any of the vendors should have these available. Just tee in the vacuum line for your recirculating air flap on the cowl. I mounted my valve to the inner fender, close the hood hinge about 6-8 inches away from the heater core inlets.
It does help with the cooling when it's really hot outside since the heater core is on the passenger side of the firewall, not out under the hood.

neonlarry · 05-24-2008, 10:08 PM

I like the newer versions better. Like one from a 90's van.

Custom 68 · 05-24-2008, 11:16 PM

I was wondering if there were different ones. What is different and is this something I can get at the local auto parts store? The air is cold but figured this is supposed to be there.
Dave

neonlarry · 05-25-2008, 02:30 AM

The newer valves have both heater lines going through them and when activated loop the coolant back to the engine through the other line. Instead of just trying to block one line, where any leakage in the valve lets hot water flow through the heater.
I'm sure local parts has them, I just don't remember exact year van I got it from (and can't take a pic right now because the kids took the digital on a trip and won't be back for a couple weeks).

Custom 68 · 05-25-2008, 02:52 AM

great, that does sound better than blocking one line. I will do some digging should be able to find one. If anybody has a pn or other info that would be appreciated.
I guess it is either open or closed?

neonlarry · 05-25-2008, 04:53 AM

Yes, either open or closed. Its to keep hot coolant out of the heater core when the A\C is on.

red71cheyenne · 05-28-2008, 11:48 AM

Another thing you can do is make sure the flap that closes off the heater core when you are on the cold side is fully closing. I had my R-12 checked at Ricks there in Spfld, and he said my door wasn't fully closing, keeping the hot air coming in. I tore the evap box apart and cleaned all that out and it works much better now. You'd be surprised how much crap collects in there after 30 years.

05-24-2008, 04:51 PM	#1
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,929	vacuum actuated heater shutoff help well ok I hope that title makes sense. Anyway I have got my AC running but have seen a valve that shuts off the hot water to the heater core that uses vacuum to operate. does anybody have a part number I know they had them on several vehicles? And how does it work is it just kindof on or off working off the AC switch or does it regulate based off the hot to cold lever? I have my inside to outside vaccum doors working but never had one of these on my original AC truck. Any help or thoughts if I need one or not would be great. Thanks Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

05-24-2008, 04:58 PM	#2
clay68c10 Senior Member Join Date: Aug 2004 Location: Centennial, CO Posts: 2,935	Re: vacuum actuated heater shutoff help Any of the vendors should have these available. Just tee in the vacuum line for your recirculating air flap on the cowl. I mounted my valve to the inner fender, close the hood hinge about 6-8 inches away from the heater core inlets. It does help with the cooling when it's really hot outside since the heater core is on the passenger side of the firewall, not out under the hood. __________________ ClusterTruck: 68 C10 Bought in 89, wrecked in 03. Slow low $ rebuild started '17. 6.0 & TKO http://67-72chevytrucks.com/vboard/s...d.php?t=788602 93 K1500 Short Step, 350, NV4500, EBL flash ECU. Vortec heads & roller cam someday... 05 Jeep Wrangler Unlimited. 3” lift & 6-speed 02 E320 the insurance total “free car” 13 Tahoe LTZ

05-24-2008, 10:08 PM	#3
neonlarry Registered User Join Date: Feb 2002 Location: Vacaville, CA Posts: 2,746	Re: vacuum actuated heater shutoff help I like the newer versions better. Like one from a 90's van. __________________ 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI

05-24-2008, 11:16 PM	#4
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,929	Re: vacuum actuated heater shutoff help I was wondering if there were different ones. What is different and is this something I can get at the local auto parts store? The air is cold but figured this is supposed to be there. Dave __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

05-25-2008, 02:30 AM	#5
neonlarry Registered User Join Date: Feb 2002 Location: Vacaville, CA Posts: 2,746	Re: vacuum actuated heater shutoff help The newer valves have both heater lines going through them and when activated loop the coolant back to the engine through the other line. Instead of just trying to block one line, where any leakage in the valve lets hot water flow through the heater. I'm sure local parts has them, I just don't remember exact year van I got it from (and can't take a pic right now because the kids took the digital on a trip and won't be back for a couple weeks). __________________ 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI

05-25-2008, 02:52 AM	#6
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,929	Re: vacuum actuated heater shutoff help great, that does sound better than blocking one line. I will do some digging should be able to find one. If anybody has a pn or other info that would be appreciated. I guess it is either open or closed? __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

05-25-2008, 04:53 AM	#7
neonlarry Registered User Join Date: Feb 2002 Location: Vacaville, CA Posts: 2,746	Re: vacuum actuated heater shutoff help Yes, either open or closed. Its to keep hot coolant out of the heater core when the A\C is on. __________________ 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI

05-28-2008, 11:48 AM	#8
red71cheyenne Back in the sticks Join Date: Jan 2001 Location: Fordland, MO Posts: 3,188	Re: vacuum actuated heater shutoff help Another thing you can do is make sure the flap that closes off the heater core when you are on the cold side is fully closing. I had my R-12 checked at Ricks there in Spfld, and he said my door wasn't fully closing, keeping the hot air coming in. I tore the evap box apart and cleaned all that out and it works much better now. You'd be surprised how much crap collects in there after 30 years. __________________ 1971 Cheyenne C-10 w/700R4 and Tuned Port Injection 1969 K5 Blazer w/Tuned Port 2010 2SS/RS Flaming Orange Camaro 2011 K1500 Suburban 2014 K1500 Pickup 2008 Nissan Altima? The wifes' hoopty



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