Mysterious "water valve" - 1993 K1500

[east302]

I believe they're vacuum operated. Dad put manually operating ones on a couple of the square body Burbs, so he could shut the hot water off to the heater box,and keep it from heating up the AC evaporator core. Gotta have all the help you can get in those hot and humid Gulf Coast summers!

Was it just a pair of ball valves on the hoses?

Seems like that would be the same concept. Open them for a couple months a year when you want heat and otherwise leave them closed.

 

[wirlybird]

Adding to that, the valve was only used on the Tahoe/Yukon/Suburbans (for 95+ at least) and not the pickups. When you turned the temperature dial to the “max” detent it closed the blower intake damper (recirc) and energized the solenoid on the firewall which then applied vacuum from the PCV fitting to the water valve, closing coolant flow to the heater core to maximize a/c performance.

On my 98 two door Tahoe it makes about two degrees dash vent temperature difference if memory serves. Nothing to write home about- with no rear air in mine, it doesn’t help those in the back much.

My 98 ex-cab truck without the water valve arguably cools the cab better since it’s smaller.

I’d assume that the 94 and under Blazers were similar, but no guarantees on that.

I found one in my '97 2 door Tahoe also, when it started leaking, and once I figured out what it was I removed it completely. It wasn't even hooked to a vacuum source from the factory so it was sort of bypassed already.
Info I could find was it was really for trucks with the rear air. Removing it helped the heater work better in my opinion!

 

[HotWheelsBurban]

Was it just a pair of ball valves on the hoses?

Seems like that would be the same concept. Open them for a couple months a year when you want heat and otherwise leave them closed.

I think so. We haven't had that truck for several years.

 

[Wildblue19]

Came up with my own solution, since I couldn't find an off the shelf setup to do what I wanted.

Added vacuum solenoid valve on intake and vacuum shutoff valve in the heater core return line. Vacuum solenoid triggered via my DIY circuit board.

Circuit board reads voltage from temperature blend door potentiometer. When the signal indicates full cold position, internal logic triggers the mini relay, closing ground and energizing the vacuum solenoid.

Fun project, my first time designing and making my own board so there was lots of learning.

 

[1998_K1500_Sub]

Here's a water valve diagram and info from the 1998 service manual, with some pictures. Some of this was discussed prior in this thread.

 

[1998_K1500_Sub]

Circuit board reads voltage from temperature blend door potentiometer. When the signal indicates full cold position, internal logic triggers the mini relay, closing ground and energizing the vacuum solenoid.

What’s the 8-pin DIP, a comparator (e.g., LM311) or simply an op-amp used as a comparator?

 

[someotherguy]

Came up with my own solution, since I couldn't find an off the shelf setup to do what I wanted.

Added vacuum solenoid valve on intake and vacuum shutoff valve in the heater core return line. Vacuum solenoid triggered via my DIY circuit board.

Circuit board reads voltage from temperature blend door potentiometer. When the signal indicates full cold position, internal logic triggers the mini relay, closing ground and energizing the vacuum solenoid.

Fun project, my first time designing and making my own board so there was lots of learning.

That's taking DIY to the next level, sir.

Richard

 

[Wildblue19]

What’s the 8-pin DIP, a comparator (e.g., LM311) or simply an op-amp used as a comparator?

Thanks for the info, I hadn't seen that before. I figured the 95+ systems had a 'max' cool detent that triggered the solenoid. Nice!

8 pin is as you suspected, op amp comparator based on the blend door full cold pot signal (~4v). I'm ME but EE basics come in handy sometimes!