Heater valve vacuum problem

[LeeRoy]

Hi,
My heater valve is opening during boost and even light driving affecting my AC air. I'm sure it's the valve as I bypassed the heater core and I get cold AC all the time.
I assume a bad or missing check valve or something else?
There is 1 check valve on the drivers side going to the metal vac line. That one is ok.
Are there others?
Any tips on how to troubleshoot?

Also, when I turn the car off the heater valve maintains a vacuum source for hours.

Thanks

[Steve Wood]

The vacuum line that goes to the firewall should have a small check valve in it to prevent boost from blowing into the AC controls and also to the vacuum storage ball that is under the fender just in front of the drivers side front tire...you can see the ball if you are laying on the ground and looking up just in front of the tire.

Now the line that runs to the firewall connects to a vacuum distribution valve and that valve also has check valves built into it.  One side of this valve goes to the reservoir ball and the other side is connected to two small hard plastic lines-one goes to the heater valve in the heater hose and the other small line goes into the car to the ac controls.

You can check the small check valves by blowing into them from the vacuum block side or where the metal lines come out.  You should not be able to blow thru them but you should be able to suck thru them.  This prevents boost from going to the AC, heater, and cruise control.  If the distribution valve on the firewall is bad, it will fail to provide vacuum to the various controls that need vacuum to operate.

Right now it sounds one of the small check valves is probably bad or missing.  They are available from the parts stores.

[Steve Wood]

The one on the firewall should be this one  https://www.oreillyauto.com/detail/c/dorman-help/dorman-help-3-16-3-16-1-4-inch-wye-y-check-valve/mtm0/47150/v/a/2665/automotive-car-1986-buick-regal?q=2+way+vacuum+check+valve&pos=0

the line on the bottom goes back to a vacuum line coming from  egr vacuum line area as I recall.  The one to the right goes to the cruise control and vacuum storage ball and the top one goes to the AC controls.

As I said, I suspect it is one of the small two way check valves in the line rather than this one, but, I have found it's a good idea to replace them all as most of them started to fail 20 years ago from age.

[LeeRoy]

Thank you. Will check.

[Just a Six?]

Steve so glad I checked this post as for years I've had weird issues with my ac on Hot days & I don't think I have any check valves in my lines. I always knew that's why my cruise control doesn't work but this explains the other issues my ac gets on hot days. Time to find a couple check valves again. Years back I picked up a half dozen but they are MIA & now that I moved last fall all my stuff is in boxes in the garage so no chance I have them anymore. I'll look for that one you posted up out here in the Great White North!
Thanks you're always a wealth of info to all of us! 

[Steve Wood]

David, it will do it in a flash!  On your cruise control, mine did not work for several years.  A couple of years ago, I decided to change some of the vacuum lines because they were old and had turned to carbon black on the outside. The one that goes to the cruise control actuator and on to the storage ball had never been touched.  When I started to remove the piece that went to the actuator, I discovered it had a crack in it on the bottom side.  Amazing how well my cruise worked when I put new hose on it.  LOL

The little check valves are usually found in any parts store in the HELP section or whatever is similar to that.  They are pretty cheap down here but you may have to throw in a relative up there.

I went and snagged a copy of the vacuum line diagram.  If your removed the egr vacuum control valve, just go straight to the two way valve on the firewall instead of to the control valve and then on to the firewall.

Good to see you ! 

[Just a Six?]

Thanks Steve I'll save this info & put them on the list with fresh oil etc. It's in the driveway now & letting the rain clean off the dust! 

[Steve Wood]

Sende some of my that rain

[LeeRoy]

Steve,

The check valve coming from the metal vac line is leaking. I did check it blowing into it and it seemed fine but it did not work with a few psi of compressed air. I think this is the major issue.

Next issue is my heater valve does work but it does not seal 100%. The valve closes and I can visually see it blocks the port but when I hooked it up to a hose water does leak. With fluid entering vacuum port side a leaks a small stream (maybe 10%) with fluid flowing the other way it maybe blocks 25%.

Also the valve was hooked up in the car with the vacuum chamber at the top which I think is upside down. Correct?
Does coolant flow into the the valve before the heater core or does it shut off coolant coming out of the heater core?

So my dilemma is do I replace this with the plastic replacement as the metal one is discontinued. Metal one is definitely more reliable. I'm worried about cracking.
This is the plastic replacement from Rock auto- https://www.rockauto.com/en/parts/acdelco,155812,heater+valve,6860
Are there metal equivalents?  I've searched and found nothing.

Thanks for the help

[Steve Wood]

I hate it when I type a long answer and it kicks me out.

Shorter version.  Vacuum goes to the bottom.  See the pic from the manual I attached.

I suspect the valve is designed to pass a little coolant to minimize core corrosion.  Lack of cooling may be caused by the fact that the condenser is old and no longer flows/cool as it once did and it was not designed for R134A which generates a lot more heat than the freon of the day.  A new condenser, new variable orifice valve and can will probably make it work a lot better. 

Highway Stars is showing temporarily out of stock on the valve.  I did not check Kirban's site.  https://www.highwaystars.net/valve-heater-flow-control-original-gm-25523118-acdelco-15-5320/

If you have not downloaded a shop manual, see the link and instructions of the first post in the General Buick Tech forum on this board and get a copy.  The wiring part is worth it's weight in gold...or more but there is a lot of good stuff in the manual beyond that.

[Steve Wood]

Wow...just looked at the price on that valve...think I would stick with the plastic one LOL

[LeeRoy]

Crazy price. And there is one on ebay for $250.

[LeeRoy]

Got everything working.

Used this one instead of the plastic replacement.

https://www.rockauto.com/en/parts/uac,HV1022c
Correction pn is Hv1022c
Thanks

[Steve Wood]

Good deal!  Glad you found one

[Just a Six?]

Wow one is $130 the other is $10 that's crazy.   
I've had my Vacuum pointing up the last 20+ years so I put it on upside down like the diagram.