samdjr74

Hi All,

I'm not going to open yet another thread on cabin heat, instead I'm wondering who has used a NAPA 660-1293 and did you use the stock heater valve vacuum line it.

Thanks,
Sam

DUB

I have not and more than likely would not. That is not the correct design of hot water shut off valve.

I prefer the metal ones offered by the major Corvette suppliers.

DUB

mikep3

https://www.corvetteforum.com/forums/c3-general/3063126-heater-bypass-valve-project-finished.html
I googled the napa number and found this. It looks like it shuts off the heater and bypass the engine side. My 78 just has a single line shut off, that leaked on a long trip this summer, it was plastic. When and if I replace it, I am going with a metal one.

samdjr74

Ok, thanks guys, just looking for options. I'm working on fixing my heating system and I'm trying to do as much research on what parts to use before jumping in. I thought the NAPA part would be a good fit because it might work off of the original vacuum line that controlled the stock heat valve. The more I think about it the more I might just put in a manually valve.

DUB

You can get a hot water shut off valve that will work off of vacuum. But the vacuum will only work in one mode...MAX A/C....if you go to any other setting...the vacuum stops and hot water flows...UNLESS you do a modification...like I did on a customers 1974 that we just got done with several moths ago. The hot water shut off valve control is controlled by the Cold-Hot roller wheel(right side)...and NOT the left roller wheel. So as long as the Cold/Hot roller wheel is all the way at the top on the "C"...the hot water is stopped...and his car gets so cold that like he said..."I could sell ice cream out of it". He has stated that in the heat of summer..the air coming out when on MAX A/C gets down to 42 degrees F in the center duct. The owner is a forum member also.

A manual shut off valve works also....but I run into may that leak when turned...not often...but it has happened many times. I prefer it being a 'no hands on' working system myself.

DUB

Mashman

I use one like that, and it works VERY well.

It's not a cutoff switch, it's a bypass. I don't know if that is a normally closed, or normally open bypass - mine is normally open, which means coolant flows to the heater core when there is no vacuum applied. When it has vacuum, it doesn't try to restrict the flow, it reroutes it, bypassing the heater core. Since it's not restricting the flow, unlike a cutoff, there is very little pressure built up. In my opinion, this is a much better solution. If you install a bypass, I would make sure you go the normally open route, that way you don't have to do anything when you have the cooling system flushed.

Some years had vacuum cutoffs, and some didn't, and when the vacuum was supplied varried for different years. I have a 72, and it did not come from the factory with a vacuum cutoff, so I had to add a vacuum supply, I installed it like later C3's, and put a vacuum switch on top of the heater core. The vacuum switch is actuated by the temperature wheel, when the wheel is all the way to cold, then vacuum is applied to the bypass valve, when it's not, the vacuum is cutoff.