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Old 08-20-2012, 11:34 PM   #1
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Default Heater valve... what hoses go to what??

I have a 80' vette with a LS1. I was just informed about using the wrong heater valve. So I found the 74781 valve I need to use from another post.

In the picture below which hose connections go where? I am hooking this up from nothing and having to get new heater hose. Thanks for the help!!!!

Click the image to open in full size.
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Old 08-20-2012, 11:48 PM   #2
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I have answered this one before in some past post..

The ports on the right side of the pictures goes to the engine. The ports on the left side of the pictures goes to the Heater core.

The 5/8" is the feed out of the block/pump to the heater core and the 3/4" is the return to the block/pump

IIRC, When vacuum is added, the coolant will be bypassed back to the block/pump. if vacuum is removed, the coolant will then flow to the heater core and allow the heater core to heat. (else it is the other way around, I can check in the morning). But you should be able to check yourself.

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Old 08-21-2012, 03:34 AM   #3
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see post 13 for a pic
GTO heater hose and valve plumbing question
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Old 08-21-2012, 08:54 AM   #4
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LOL.. that is the thread that I had posted the answer before.. Post #12.. .just before the picture Chris posted..
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Old 08-21-2012, 10:20 AM   #5
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Yall are awesome! Thank you!

I shall install this tonight
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Old 08-21-2012, 11:07 AM   #6
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I'd start my testing the climate control (heater) system on your Vette. Does the vacuum hose to the existing heater valve have vacuum with the climate control (heater) in the OFF position, or in the ON position? If it indeed has vacuum when in the OFF position, then it will be plug and play.

As this heater valve is a bypass type, it routes the hot water back to the water pump (5/8" from pump to the heater valve, then 3/4" back to the pump). This occurrs when vacuum is applied to the heater valve. When the vacuum is off, the valve will direct the water to the heater core. The heater valve is normally open (NO). As such, whatever control system you have for your climate control (heater), it must provide vacuum to the heater valve in the OFF position, and turn the vacuum off when in the ON (heat) position.

My climate control system is electronic, so I had to use a vacuum switching valve (VSV) with the correct logic. I used an Echlin #2-26873 (NAPA #CRB 226873) which is (NO) normally open (allows vacuum through the valve) and venting in closed or activated (+12V). It's application is: Toyota Camry 92-01, Celica 92-99. Venting is important as you need to dump the residual vacuum in the hose that connects to the heater valve, otherwise the heater valve will remain closed.

Hope my explanation is clear.

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Old 08-21-2012, 12:33 PM   #7
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I like your solution. I've got an LS swap with Vintage Air (electric heater valve). I found 4 port electrics (Lincoln?) but they were really expensive.
Btw, I'm pretty sure 60s-70s GM cars used a normally open 2 port HCV that closed with vacuum when AC was on, heat off.
Both my LS swaps are currently using 2 port heater valves now but would like to switch to a 4 port. No overheating but I've noticed the temp goes from cold at startup and rises abruptly until it stabilizes.

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I'd start my testing the climate control (heater) system on your Vette. Does the vacuum hose to the existing heater valve have vacuum with the climate control (heater) in the OFF position, or in the ON position? If it indeed has vacuum when in the OFF position, then it will be plug and play.

As this heater valve is a bypass type, it routes the hot water back to the water pump (5/8" from pump to the heater valve, then 3/4" back to the pump). This occurrs when vacuum is applied to the heater valve. When the vacuum is off, the valve will direct the water to the heater core. The heater valve is normally open (NO). As such, whatever control system you have for your climate control (heater), it must provide vacuum to the heater valve in the OFF position, and turn the vacuum off when in the ON (heat) position.

My climate control system is electronic, so I had to use a vacuum switching valve (VSV) with the correct logic. I used an Echlin #2-26873 (NAPA #CRB 226873) which is (NO) normally open (allows vacuum through the valve) and venting in closed or activated (+12V). It's application is: Toyota Camry 92-01, Celica 92-99. Venting is important as you need to dump the residual vacuum in the hose that connects to the heater valve, otherwise the heater valve will remain closed.

Hope my explanation is clear.

Andy1

Last edited by garys 68; 08-21-2012 at 12:38 PM..
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Old 08-21-2012, 03:19 PM   #8
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Though I used the Fbody heater control valve (HCV) simply because it is a known, there may be a better choice if someone wants to check it out. A HCV from a '90 Astro van is a neater package than the Fbody HCV and it is a bypass type (90% sure anyway). It's control logic is the same as the Fbody.

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Old 08-22-2012, 12:20 AM   #9
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Beware!

I bought the 74781 in the first post and shortly after it started leaking from the stem or rod that extends into the heater valve thats actuated by vacuum.

I was like Really! Win The Future???

I'm on my second one now (Made by Factory Air) but I have my eye on it.

I like the one posted from the Astro. If this fails again I'm going to give it a try.

It looks like its a bit more of an enclosed design which would be beneficial from where mine started to leak but that may not be the case as I cant see whats on the other side.

The ends do not look to be staggered in size either.
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Old 08-22-2012, 01:24 AM   #10
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I also am on my second one. The first one lasted about four plus years and the second one has been in service for two plus years now. Same leak as you stated.

But like all thing, they are just cheap and are not expected to last forever.

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Old 08-22-2012, 07:22 AM   #11
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They're $13, that pretty much tells you "Made in China"....buy a spare.
Biggest problem is there's no guarantee the $39 version on ebay is any better.
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Old 08-22-2012, 08:07 AM   #12
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Quote:
Originally Posted by bczee View Post
I also am on my second one. The first one lasted about four plus years and the second one has been in service for two plus years now. Same leak as you stated.

But like all thing, they are just cheap and are not expected to last forever.

BC
Four years I could have lived with. I had mine on for about 2 months when it went south.

Second one is still holding now at about 6 months.


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They're $13, that pretty much tells you "Made in China"....buy a spare.
Biggest problem is there's no guarantee the $39 version on ebay is any better.

I hear you. I just despise coolant leaks. Well... any fluid leak for that matter.. But the only ones I'm always dealing with on this swap/car are coolant leaks.

First was my 26+ year heater core (Ok, that one was expected). Then it was garbage heater hose, then it was garbage clamps. Now the garbage heater valve.

None of which I went out of my way to say... Hey! whats the cheapest POS component I can put on my car today that will possibly leave me stranded later?

Just frustrating when you think about the potential these small dollar items have to torpedo all your hard work.
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Old 08-22-2012, 10:51 AM   #13
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I had a similar but opposite experience with the HCV on my Explorer. Short lived valve was made in Germany, replacement was made in China and it never failed.

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Old 08-22-2012, 12:42 PM   #14
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This is the valve I use. It sits nice and flat against the wheel well and so far, hasnt leaked. The car has been down for a while, so Im going to buy a new one as a back up in case the time wasnt kind to it.

When I was driving the car, it worked perfect. No leaks or anything.

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Old 08-22-2012, 12:42 PM
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250, 91, air, bypass, celica, chevrolet, control, core, corvette, factory, ford, heater, hose, inlet, valve


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