Mysterious "water valve" - 1993 K1500

[Wildblue19]

While reading through the 1993 C/K 1500 electrical systems manual (thank you @hatzie ), I stumbled across this tidbit in the AC section:

"The Water Valve is a normally open solenoid that allows coolant to flow through the heater core. The Water Valve closes when the temperature setting on the Heater and A/C Controller is in the full Cold position. "
[Pg. 153]

It further describes the location as on the right rear of the intake; there is only the crappy quick disconnect fitting into a factory hose on my truck.

I understand coolant shutoff valves for AC performance. I tested a manual shutoff valve in my 93 suburban and it decreased vent temps by over 5°. I also know for a fact my truck has no such built in valve.

This section is the only place the phrase 'water valve' is mentioned in the entire manual, and I was unable to find a wiring diagram in the manual showing how the solenoid is switched and where it is mounted.

If I am missing parts, or maybe this was an optional thing for some trucks, I'm not sure. Chime in if you've seen one factory!

 

[someotherguy]

It might be an error in the manual. My 1994 C/K service manual describes vacuum hoses in the A/C section....clearly a cut-and-past from the prior generation of trucks.

Richard

 

[Wildblue19]

I think that may be the case as well, which is unfortunate since my experience has shown AC improvement with the core blocked off.

 

[yevgenievich]

I added one before when I had 91 suburban. I just tied it to vacuum and capped vacuum off for it in colder months.

 

[454cid]

I believe the valve was an SUV thing. It required a electrically operated vacuum switch, I think.....same type of thing that Dodge used to engage the front axle, I think.

 

[HotWheelsBurban]

I added one before when I had 91 suburban. I just tied it to vacuum and capped vacuum off for it in colder months.

Yes, square body Burbs and trucks had no factory heater control valve. The 400 SUVs with rear heater have one, in the rubber hoses that go on the passenger side of the engine compartment ( and under the truck to the rear heater core). They're plastic, and are prone to cracking from age and being too heavy handed tightening the hose clamps. Had this issue on the first 99 Burb. Dad finally put brass tubing,from a hobby shop, in the hose nipples, and that helped.

 

[Wildblue19]

Yes, square body Burbs and trucks had no factory heater control valve. The 400 SUVs with rear heater have one, in the rubber hoses that go on the passenger side of the engine compartment ( and under the truck to the rear heater core). They're plastic, and are prone to cracking from age and being too heavy handed tightening the hose clamps. Had this issue on the first 99 Burb. Dad finally put brass tubing,from a hobby shop, in the hose nipples, and that helped.

Thanks for the info. Was it a vacuum shutoff valve or electronic one? I'm going to try and implement a shutoff in my '93; just need to figure out the best way to actuate it automatically with HVAC controls...

 

[east302]

I believe the valve was an SUV thing. It required a electrically operated vacuum switch, I think.....same type of thing that Dodge used to engage the front axle, I think.

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.

 

[HotWheelsBurban]

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!

 

[yevgenievich]

Late 80's f body ac control panel had a vacuum port for the heater diverter valve. Probably other gm vehicles as well. Adding one with a vacuum switch actuated by existing controls should be relatively simple. For as little as I used heater on the 91 burb, I never did auto control for it.