troyd

Greetings from All Thumbs Automotive.....

So things have been relatively uneventful with the Olds of late....until recently. So the AC is now only blowing through the floor......so, knowing that the air flow is controlled by vacuum.....I figured the vacuum canister on the firewall was kaput. No such luck. Replaced it and still no joy.

So, one hose is connected to a vacuum port on the manifold and the other goes through the firewall and I assume that it connects to the heater control in the dash. That’s pretty much it, right? So, the vacuum hose that runs to the control panel is probably a pre-Mayan artifact (the one connected to the manifold port is new-ish).....so, that would be the next likely culprit, right?

Your thoughts gladly welcome...

Fun71

Did you verify there is vacuum pulling on the hose that goes to the dash controls? Maybe something is blocking the port in the vacuum reservoir? Maybe connect the hose from the dash directly to the manifold vacuum source, bypassing the reservoir? Just thinking to verify there is vacuum to the dash control hose before diving under the dash.

joe_padavano

Before wasting a lot of time and money replacing parts that may or may not be the cause of the problem, you MIGHT want to try some no-cost troubleshooting first. When the HVAC system looses vacuum, it defaults to output from the heater and defroster ducts as a failsafe. figure out why there's no vacuum. Could be the hose coming from the intake manifold. Could be the check valve. Could be a bad or disconnected hose under the dash. Could be the vacuum switch in the control head. Could be a bad vacuum actuator on the HVAC box under the dash. The CSM has the hose plumbing diagram and a matrix of which connections get vacuum for each position of the control slider. That and a vacuum gauge are probably the first things you should use.

cfair

What year & model are you working on here?

Your year Chassis Service Manual or Assembly manual should have a vacuum diagram for your car and system. When AC vacuum controls fail, usually the vacuum hose ends stretched over the metal ports / diaphragms either split or crack from the stress of being stretched for a few decades. Design wise the vacuum works against springs to move levers. If the springs are missing or diaphragms have leaks, levers & doors don’t move.

A handheld vacuum pump can help diagnose individual components like hoses and diaphragms, but can’t really substitute for a running engine - they don’t have enough volume. It could be that your replacement reservoir is bad too. You might try hooking up the vacuum reservoir connections 2 ways to see if it behaves differently when you swap engine connection for the other one that goes through the firewall.

From the intake manifold, the vacuum usually travels to a reservoir (Bakelite plastic or one that looks like a tin can). From the reservoir you’ll have an outbound supply line which goes through the firewall to whatever vacuum accessories you have. Often this is just the AC system, but optionally can include vacuum trunk release and/or vacuum power door locks for pre-70’s cars. Sometimes there is a one way valve on the line between the reservoir and AC unit. It’s there to prevent an engine vacuum leak in case of AC system leak.

Olds color coded the vacuum lines between the AC controller and the diaphragms. First check that all of your lines, possibly except the input line from the reservoirs are color coded. If your lines are good shape, chances are you’ve connected the wrong port to a diaphragm or 2. Depending on your car, check Fusicks or the reproduction places like OPGI for a replacement set of hoses. If you have a big car - 88/98/Starfire, you’re probably not going to find anything, so a boneyard can help, or you can make your own replacements.

If your lines allow vacuum leaks or are not connected, you can substitute a correct size new vacuum line, but if it were me, I’d put a label on it corresponding to the factory color code like “Chartreuse” using blue tape so that 5 years from now you can figure out what you did. If you do go the route of making your own vacuum lines cut them all 2-3 inches too long so that when they wear at the end, you can snip them a few times to make a good connection down the road.

If not, someone may have been in there before and done something wrong. It sounds like you have vacuum to the system, it’s just the one diaphragm that’s not working - either because the diaphragm is bad, or maybe because the spring that diaphragm works against is missing and not pulling it back. It could also be that your vacuum distribution switch is bad/leaky. This is pretty rare though.

My mid-60’s big cars are simple and work great, but there were some major changes into the 70’s and beyond that seemed to make them more finicky as time went on. They can be made to work though, my ‘66 Starfire with A/C, door looks and trunk release holds vacuum for 24 hours and more. Personally, I find that amazing with 55 year old components.

Hope this is a good start.
Chris

troyd

Thanks guys.....should have started out, it's a 71 Cutlass...and this is a problem that has recently, very recently, presented itself. IE everything was fine until it just wasn't.....so, I'm eliminating the whole trying to isolate, identify and un-pickle something that was half assed 20 years ago.....IE. I'm looking for a part that just stopped doing what it was supposed to do.

Right, so, I'm down with what you guys are saying here......and to Mr. P's point, yes, I'm looking for the logical (re not throw parts at it and **** money away and hope for the best) way to approach this. I mean vacuum hose seems to grow in my garage. I got miles of it....so replacing vacuum hoses just for the sake of it notwithstanding.

So, and again, I'm thinking out loud here really trying to get my mind wrapped around this

So, I got the CSM and the hose routing Check. What I'm thinking here is that the whole she-bang is based on a process that starts from the manifold port sucking air in and harnessing that vacuum (opening actuators) to allow that vacuum to open the diverters under the dash......so, if I'm troubleshooting.....start at the manifold port and work backwards, right? Safe to assume that there is vacuum being created (I mean, the power brakes work....so, something is producing vacuum, right?). So, yes, there is a hose (in good nick that runs to the canister on the firewall. A new one at that. (so, assuming that it isn't defective).....the other hose runs to the little thing conected to the lever on the control panel........so my next move, as Kenneth (I think said) would be to bypass the canister and apply suction via vacuum pump (or we could just connect it to a manifold vacuum port....no joy there, in my mind would be the hose through the firewall to the control panel. ...

So, my questions are this......does this seem like the logical way to go about this? And, if so...I guess what I'm really asking is are there common failure points (beyond the canister and pre-Mayan vacuum hoses) in the system?

Again...apologize for what my appear to be nonsensical ramblings and appreciate the feedback and patience.

Cheers,

Troy

joe_padavano

Troy,

Yes, that is the correct process. Start at the manifold and work back. I would take a vacuum gauge and check the reading at each point in the system, starting right at that manifold port. Yeah, it's unlikely that it's blocked, but not impossible and it takes a second to check it. Move to the hose that goes into the vac canister, then the one coming out, etc, etc.

cfair

Troy,
Not nonsensical ramblings. We’ve all been there. Something suddenly just doesn’t work. Sometimes on Sunday night at 10:00 p.m..

If the brakes work and some other AC functions work, like the heater, it sounds like you’ve got vacuum to the controller.

Sounds like one or more arterial lines (aka the controller output lines) ain’t right. I haven’t crawled under a ‘71 much, if ever, but if you can physically see the controller connections and the diagphram connections, you can trouble shoot them. In my older cars, I usually have to remove the cabin A/C manifold to see the controller located above it.

Look at your CSM and you’ll see the controller routes incoming vacuum signal to a diaphragm/spring combination based on your demand. Mine does this routing using a rotary valve which spins to different clock positions and hence different vacuum lines arranged in a circle when you push the function buttons. Not every pin on the controller needs a vacuum line. See your CSM for which ones should be unused and blocked.

Once you can see and get at the components, it’s pretty quick to test individual diaphragms with a vacuum pump. I’d start testing the ones on the distribution manifold since they’re at the center of the system.

• If you apply vacuum and a rod doesn’t move or a door doesn’t make moving sound, the rubber inside the diaphragm may have a hole
• If you see a lever disconnected from a diaphragm that’s a problem - i.e. the vacuum side works great, but isn’t connected to the lever or door its supposed to move.
• If you don’t see a return spring pulling against the diaphragm, once it gets vacuum once, that’s where it stays - i.e. the return spring can’t return it to the starting position.

Your CSM really is the authority here, just follow the design with existing or new hoses (carefully labeled) & you’ll be back in business.

Hope that helps.
Chris

Vintage Chief

Troy - If you don’t own a vacuum gauge - buy one ASAP. You will be sooooo glad you did. An extremely useful tool. Removes any guesswork. A shame about the Mayans eh?

troyd

Crying shame. Poor bastards.

Vacuum gauge. Got it.

NORM! Still trying to organize a trip your way...... ugh, the restaurant business has been a nightmare the past what seems like a lifetime.....but, we are coming that way. I haven’t seen our rental in Fayetteville in close to 2 years.....the rent check still comes but, I probably ought to see if the house is still actually there.....

‘Preciate you guys patience with the neophytes

Cheers,

Troy

Vintage Chief

Stop in any time Troy. Good luck the AC.

cfair

Troy,
These cars have been with me for 40 years. I’m well north of 50 & still feel like a neophyte a lot of days. Never feel bad about asking questions here.

Part of the fun for me is that there are systems yet-to-discover or settings yet-to-discover. Like you’re going through with the AC stuff today. Or like I’ve gone through with a bunch of seemingly-simple stuff over the past few decades. As the professional mechanics age into retirement, their knowledge is lost. So each of us has to figure out once-known settings and knowledge anew. At least by sharing what we know here, the information we learn (right & wrong) is captured here and lost a little less often.

For example, transmissions are still mostly a mystery to me. I haven’t rebuilt an engine. Suspensions make me nervous since the spring loads can really hurt you during repairs. Between suspensions & brakes, I choose to leave those to professionals. Cuz if I get them wrong when I’m learning, people could get hurt. Too high a price.

But for stuff like windows, electrical, convertible top hydraulics, fun vacuum operated options? Sure, I’ll have a go. If I get it wrong, the harm is the top doesn’t go up, or the window, or the doors don’t lock & I hear a vacuum hiss. Not safety-related. No big deal, it’s an old car!

Let me know if you need me to post the ‘66 big car vacuum diagrams. I suspect there irrelevant to your ‘71, but there’s a off chance Olds was somewhat consistent with the color codings and the ports.

Cheers
cf

troyd

So, I know you guys are glued to the edge of your seats..... crusty, pre-Mayan vacuum hose was about disintegrated coming through the firewall so a little bit of time fumbling behind the dash (great fun) and pulling hose through connect to canister and we are good to go.....flappers are flapping appropriately.

Vintage Chief

Troy - Glad you found & fixed the issue. Happy flapping.

cfair

Congratulations on the fix and thanks for the echo.

Great feeling when you get something working as it should.

cheers
cf