AC selection rotary valve
June 19th, 2018, 08:54 AM
#1
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Location: Bastrop, Texas (near Austin)
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AC selection rotary valve
Here's a good one. On my 65 Starfire, the vent system (no AC) is operated by a vacuum selector with pushbuttons. The pushbuttons rotate a vacuum valve to route the vacuum to the appropriate servo (left vent, right vent, both, heat, defrost) None of this works. I've tested all but one of the servos and they are good and I am getting vacuum. It appears the problem is in the rotary valve. A guy on the OCA facebook page was kind enough to open his up and show what it looks like. It looks like two aluminum halves that mate together with some sort of felt button in the very center. One would expect to see some sort of o-rings or raised rubber areas to seal, but this one is straight metal to metal from what it appears. I would think it wouldn't seal well enough to hold vacuum to open the servos but I'm wondering if when they were manufactured, that perhaps the mating surfaces were machined very smooth so they mated pretty tight, creating enough seal to open the servos. I was wondering if anyone has ever worked on one of these and repaired it. As far as I can tell, that valve is not available. I can find used ones on Ebay but who knows if they work. Fusick sells a rebuilt one (entire assembly) but for 250.00 I thought I'd try myself. I was thinking that perhaps the surface becomes rough over the years causing it to leak. Perhaps taking it apart and putting fine sandpaper flat on a surface and carefully sanding both surfaces smooth again might fix it? Or maybe what ever hardware holds the two tight together may have worn out? The fella said that felt washer appears to have oil on it so perhaps that aids in the seal. Anyone worked on one before? This is one that has the multi pushbuttons like a car radio but I think the mechanics of those valves are probably all the same in those years. I've not yet taken mine out because I can't figure out how to get to the bolts. GM definitely had a better idea when they started making dashes with removable front panels so you don't have to work from behind!
Thanks guys and gals! PS, I'll attach a picture of the valve the guy posted.
John
Thanks guys and gals! PS, I'll attach a picture of the valve the guy posted.
John
June 19th, 2018, 09:45 AM
#2
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Location: St. Paul Minnesota
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Its not only about getting it "smooth". Its about "mating" the two parts.
1. I would try a plate of glass with some 400 to 600 lapping compound. A few passes to see it they are flat.
2. Then put 600 or so lapping compound between the two parts and rotating them. Perhaps you only need to do steps 2 through 5.
3. CLEAN all the residue and lapping compound off well.
4. Apply a very small amount of Lubriplate between the two parts.
5. re-assemble and try it out.
Good luck
1. I would try a plate of glass with some 400 to 600 lapping compound. A few passes to see it they are flat.
2. Then put 600 or so lapping compound between the two parts and rotating them. Perhaps you only need to do steps 2 through 5.
3. CLEAN all the residue and lapping compound off well.
4. Apply a very small amount of Lubriplate between the two parts.
5. re-assemble and try it out.
Good luck
June 19th, 2018, 09:55 AM
#3
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Location: Bastrop, Texas (near Austin)
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Its not only about getting it "smooth". Its about "mating" the two parts.
1. I would try a plate of glass with some 400 to 600 lapping compound. A few passes to see it they are flat.
2. Then put 600 or so lapping compound between the two parts and rotating them. Perhaps you only need to do steps 2 through 5.
3. CLEAN all the residue and lapping compound off well.
4. Apply a very small amount of Lubriplate between the two parts.
5. re-assemble and try it out.
Good luck
1. I would try a plate of glass with some 400 to 600 lapping compound. A few passes to see it they are flat.
2. Then put 600 or so lapping compound between the two parts and rotating them. Perhaps you only need to do steps 2 through 5.
3. CLEAN all the residue and lapping compound off well.
4. Apply a very small amount of Lubriplate between the two parts.
5. re-assemble and try it out.
Good luck
Thanks for the tip, sounds like a great way to try to fix it.
June 19th, 2018, 10:26 AM
#4
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Location: St. Paul Minnesota
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Hi Ralph and thanks! I don't have any lapping compound, could I lay fine grit sandpaper (I have up to 2000 grit) flat on glass and use that do you think
Sandpaper can bunch up or have "lumps" with adhesive. Its ok to smooth washers and such, but you are trying to make a "sealing surface".
or should I go ahead and procure the compound?
I would just buy a small can, it can't be that expensive. I think you can buy it at a local automotive supply or industrial supply.....when you go buy a small piece of glass. Get some isopropyl alcohol and maybe "Brake cleaner".
So what you suggest is to take a piece of glass, and smear the compound directly on the glass, then work the halves of the valve across the compounded glass?
Yes, if you use step 1 to check for flatness.
Sure can't get a flatter surface than that. I like the idea of lapping the parts together like valve grinding..
You are "mating" the two halves as they rotate, like lapping valves. Valve grinding is grinding, valve lapping is lapping a ground valve.
Rotate the parts together as if they were assembled, with lapping compound between them for a good seal.
Perhaps I should just go ahead and find the compound. Probably Amazon would have it.
Help your local business, buy from them. They might even let you rub some between your fingers. See what grit sizes they have or can order.
Thanks for the tip, sounds like a great way to try to fix it.
Sandpaper can bunch up or have "lumps" with adhesive. Its ok to smooth washers and such, but you are trying to make a "sealing surface".
or should I go ahead and procure the compound?
I would just buy a small can, it can't be that expensive. I think you can buy it at a local automotive supply or industrial supply.....when you go buy a small piece of glass. Get some isopropyl alcohol and maybe "Brake cleaner".
So what you suggest is to take a piece of glass, and smear the compound directly on the glass, then work the halves of the valve across the compounded glass?
Yes, if you use step 1 to check for flatness.
Sure can't get a flatter surface than that. I like the idea of lapping the parts together like valve grinding..
You are "mating" the two halves as they rotate, like lapping valves. Valve grinding is grinding, valve lapping is lapping a ground valve.
Rotate the parts together as if they were assembled, with lapping compound between them for a good seal.
Perhaps I should just go ahead and find the compound. Probably Amazon would have it.
Help your local business, buy from them. They might even let you rub some between your fingers. See what grit sizes they have or can order.
Thanks for the tip, sounds like a great way to try to fix it.
June 19th, 2018, 02:31 PM
#5
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Join Date: Mar 2007
Location: Northern VA
Posts: 47,259
I would make very sure the valve is bad BEFORE tearing into it. There are three possible valve failure modes.
1. The valve is leaking. If this were the case, you would hear a loud hissing noise coming from it when the engine is running.
2. The valve is plugged internally. This may or may not be something you can dislodge without disassembly.
3. The shaft is broken and the valve is not rotating.
Before tearing anything apart, have you verified that you have vacuum on the inlet to the valve (ok, technically, that port is the outlet...
)? It is far more likely that the hose is bad than the valve.
I would also strongly suggest that you get a Chassis Service Manual, which describes this system in detail.
1. The valve is leaking. If this were the case, you would hear a loud hissing noise coming from it when the engine is running.
2. The valve is plugged internally. This may or may not be something you can dislodge without disassembly.
3. The shaft is broken and the valve is not rotating.
Before tearing anything apart, have you verified that you have vacuum on the inlet to the valve (ok, technically, that port is the outlet...
)? It is far more likely that the hose is bad than the valve.I would also strongly suggest that you get a Chassis Service Manual, which describes this system in detail.
June 19th, 2018, 03:25 PM
#6
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Join Date: Mar 2018
Location: Bastrop, Texas (near Austin)
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I would make very sure the valve is bad BEFORE tearing into it. There are three possible valve failure modes.
1. The valve is leaking. If this were the case, you would hear a loud hissing noise coming from it when the engine is running.
2. The valve is plugged internally. This may or may not be something you can dislodge without disassembly.
3. The shaft is broken and the valve is not rotating.
Before tearing anything apart, have you verified that you have vacuum on the inlet to the valve (ok, technically, that port is the outlet...)? It is far more likely that the hose is bad than the valve.
I would also strongly suggest that you get a Chassis Service Manual, which describes this system in detail.
1. The valve is leaking. If this were the case, you would hear a loud hissing noise coming from it when the engine is running.
2. The valve is plugged internally. This may or may not be something you can dislodge without disassembly.
3. The shaft is broken and the valve is not rotating.
Before tearing anything apart, have you verified that you have vacuum on the inlet to the valve (ok, technically, that port is the outlet...
)? It is far more likely that the hose is bad than the valve.I would also strongly suggest that you get a Chassis Service Manual, which describes this system in detail.
Hi Joe,
Thanks for the tips! could be plugged since it is pulling a tiny bit of vacuum.
Yes, the first thing I checked was the vacuum hoses hoping it was that simple. One of the servo's barely moves when you switch it one way so it is trying. I do have the factory manuals (Body, chassis, parts and illustration manuals) but it's not real clear about how to get this part out. I am thinking that the radio needs to come out to give you room to get your hands in there and maybe I can get the clock out and fix it too while everything is out. Then I can get the unit in my hand, connected to the vacuum source and do some more testing. It appears that this circuit has reduced vacuum to begin with..When you pull the vacuum line off the reserve tank, it has a sort of a pointy end to it. It is connected directly to the same vacuum line as the reserve tank for the trunk (car has two), and it has twice as much suction. No sure why this is but maybe full manifold vacuum would ruin the diaphragm in the servos. Who knows. It is very odd that the piece relies on metal to metal contact for a seal.
Cheers,
John
June 19th, 2018, 03:31 PM
#7
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Join Date: Mar 2007
Location: Northern VA
Posts: 47,259
Did you actually check vacuum on the hose from the engine to the control head? Your post isn't clear on that.
If I remember, there are three screws that hold the control head to the dash. On my 67 I removed the HVAC box under the dash (I had to replace the heater core) which gave me plenty of room to get my head up under the dash and see those screws to remove them. You want to remove the entire control head from the dash first, then verify that the pushbutton mechanism is working properly to rotate the vacuum switch.
If I remember, there are three screws that hold the control head to the dash. On my 67 I removed the HVAC box under the dash (I had to replace the heater core) which gave me plenty of room to get my head up under the dash and see those screws to remove them. You want to remove the entire control head from the dash first, then verify that the pushbutton mechanism is working properly to rotate the vacuum switch.
June 20th, 2018, 08:48 AM
#8
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Location: Bastrop, Texas (near Austin)
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Did you actually check vacuum on the hose from the engine to the control head? Your post isn't clear on that.
If I remember, there are three screws that hold the control head to the dash. On my 67 I removed the HVAC box under the dash (I had to replace the heater core) which gave me plenty of room to get my head up under the dash and see those screws to remove them. You want to remove the entire control head from the dash first, then verify that the pushbutton mechanism is working properly to rotate the vacuum switch.
If I remember, there are three screws that hold the control head to the dash. On my 67 I removed the HVAC box under the dash (I had to replace the heater core) which gave me plenty of room to get my head up under the dash and see those screws to remove them. You want to remove the entire control head from the dash first, then verify that the pushbutton mechanism is working properly to rotate the vacuum switch.
As much as I could. I pinched it as far as I could reach it and it held suction with the miti-vac connected under the hood. I can't reach where it is connected to the valve without pulling the assembly but it "looks" okay and none of the others were bad or soft at all. In fact they felt really good and were original because they have their color coded stripes. If it's leaking it would have to be at the very end where it connects. It is possible, but given the condition of the other hoses under there, I doubt it. I did order a section of that size hose to replace the main one just in case since it does go to the engine compartment The car lived in a cool climate it's entire life until now so I think time has been kind to the rubber parts! :-)
I'm going to pull the radio out this weekend and see if that will afford me room to get in there and get that thing out so we can have a better look.
July 9th, 2018, 08:23 AM
#10
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Location: Bastrop, Texas (near Austin)
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Did you actually check vacuum on the hose from the engine to the control head? Your post isn't clear on that.
If I remember, there are three screws that hold the control head to the dash. On my 67 I removed the HVAC box under the dash (I had to replace the heater core) which gave me plenty of room to get my head up under the dash and see those screws to remove them. You want to remove the entire control head from the dash first, then verify that the pushbutton mechanism is working properly to rotate the vacuum switch.
If I remember, there are three screws that hold the control head to the dash. On my 67 I removed the HVAC box under the dash (I had to replace the heater core) which gave me plenty of room to get my head up under the dash and see those screws to remove them. You want to remove the entire control head from the dash first, then verify that the pushbutton mechanism is working properly to rotate the vacuum switch.
July 9th, 2018, 09:28 AM
#11
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Location: Bastrop, Texas (near Austin)
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Just saw some one selling one of these on a facebook page.
https://www.facebook.com/GratefulPar...69023016568496
Somehow the link doesn't show up. Go to Facebook and /GratefulParts
https://www.facebook.com/GratefulPar...69023016568496
Somehow the link doesn't show up. Go to Facebook and /GratefulParts
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