Ok, I got frustrated with all the hot air that my truck would insist on blowing out of the vents, even with the dial turned all the way to cold. It would come out a lot warmer than ambient temperatures even with the cut off valve that I had installed.
I found out that the cut off valve was not doing it's job, it was still allowing coolant to circulate in the heater core.
So this time I got a different valve, a coolant shut off valve for a 1987 Audi 5000 turbo. It's a spring loaded gate valve that completely shuts off the flow of coolant. When closed it's sort of like a reed valve in that you can blow in one side hard enough to overcome the spring it will allow flow, but if you turn it around and blow into the other side, the pressure pushes the gate against the seal and will not allow ANY flow, no matter how high the pressure. The housing would blow apart before anything would flow in that direction.
Here's what they look like.
The part number is: 431.819.809.A

I bought two of them and installed them both with the lever side facing the engine. That way ANY pressure waves that come up through the heater hoses are stopped cold in thier tracks with these nifty valves.


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On to the control relay. This one you have to go to the VW/Audi dealer to get, but it's less than $10.00 for the unit so don't bother looking around for anything better.
Part number: 191.906.283.A
It's perfectly suited for this task. It's a vacuum solinoid that turns on a vacuum signal when you energize the relay. When you turn it off it vents the driven line to the atmosphere so the item that you are controlling with it returns to it's default position. In this case, the heater valves open back up. Hook up the vacuum source to the outer nipple and the one going to the heater valves on the middle one.

Also put a tee in the source line so you have a good way to get source vacuum.

Now about powering the relay, I was lucky and had an old fuel injection plug laying around the shop that fit perfectly as the plug to power the relay. But they are not readily available to the general public unless you want to do some serious scrounging in junkyards or go to the VW dealer and buy all the little individual pieces to make the plug. The parts are available if you want to go that route, and it's the best one to take.
An easier route would be to go get some of those 1/8" wide female spade connectors and splice them to the 18 or 20 guage wire that you would use to power that relay and then wrap them with several rounds of electrical tape. Use enough tape so that it would support the connector inside the hole while it's connected to the relay.


From there it's a simple task to get a two pole on/off switch, get some power from under the dash and run it to that relay and from there to ground.

Test drive. Get out on the freeway and the heater now blows EXACTLY the same temperature as outside the truck, even with the heater turned all the way to hot. No more warm air! And turning on the AC results in refrigerator quality cold air coming out.

 

Thanks for the post Kwik. I've been waiting for the info and looks like a worthwhile mod.

 

Thanks for the solution to this pita problem...one question though. Do you think the coolant shutoff valve is really necessary on the coolant return line from the heater core? Once again, great job Kwik!!!

 

Kwik have you studied the normal flow of coolant through the heater core? I am wandering if there may be a starvation of coolant on the out flow side of the core and a backup (no flow condition) in the in flow side of the core. In other words, the truck was designed to always flow coolant to that circuit. If you stop that flow you are isolating the heater core but are you also isolating anything upstream or downstream of the core that should have coolant flow. May be a mute concern but I'd hate to burn something up.

 

sgrol...so maybe like a bypass valve instead of a shutoff valve? I love the twists and turns to these mods. The ideas keep flowing - um just like the coolant to my heater core. I really need to do something about it.

 

Just thinking out loud about the extra switch to power the unit, so bear with me. I don't know how the temp selector dial works, but could you wire the shutoff/bypass valve to that dial so that when the selector is on the cold side all the way it would autmatically engage the valve? That way if you just want cool outside air or the A/C it would engage for you without an extra switch to flip??

 

I like the idea Kwik. I am wondering if you have ESOP and put manual hubs in, if you could use the hublock solenoid? The vaccuum lines are their all you would have to do is the power plug.

 

FWIW I have been running a shut-off valve for about 150,000 miles with no ill effect. Just really cool AC even at almost 200,000 on the truck. I think at the time I did it I reduced my AC temp by about 5 degrees.

 

Hmm I like that idea, and I am thinking it would work pretty good instead of setting up a seperate siliniod expecially since I have manual hubs. have to look into that one a little more.
Great idea Kwik.

 

I don't have ESOF on my truck, it's all levers. Sounds like utilizing the ESOF for that would work perfectly after you convert it over to levers.

 

I can't wait for the cool air!!

 

I just got back from a long drive and was surprised to learn this fact: As long as I'm moving on the freeway and lot's of cool air moving over the hood, the air coming out of the vents was nice and cool. As soon as I slowed down for a light and the air stopped flowing over the hood, the air coming out immediatly warmed up. It's like it was sucking air from the top of the warm engine hood. As soon as I sped back up again, it cooled off.
I think this is as good as it's going to get. I know for sure that the coolant flow is turned off because I can turn the heater all the way to hot and no change in temperature at the vents.

 

Snap on sells a great little thermometer with a long stem that sits in the vents nicely. I will try and get a picture and post it.. before my heater mod i got lower 40s out of the vents. After my manual gate valve install it usually hangs around 38-40 idle or running down the road, and it gets plenty hot here in texas....

 

And what does snap on charge for that $1.99 walmart special meat thermometer?

 

They are around $10.

The a/c will always blow colder going down the road than at idle. Thats just a fact. In my old car, I mounted 2 large electric fans on the condenser to help fight that since it gets so hot here in texas.

MrB sent me a pic of his valve install and I did it exaclty the same. My a/c was blowing in the low to mid 40s on the hot days and now it stays between 32-38 with the cutoff valve. It will be over 100 out and the wife will complain to me its too cold.