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  #1  
Old 06-07-2019, 03:34 PM
07Vulcan 07Vulcan is offline
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Default Vaccum guage

What is normal vaccum at the vacuum canister? So far im pulling about 20hg. Still loose ac to the defrost vents. But the vacuum canister helped alot. I can now drive with regular a/c and it not default to the defrost vent. But max air still doesnt work and defaults bad to the defrost vents when it is selected. I cannot find a line broken or leaking any where. I have pulled vacuum with a hand pump and they hold vacuum. I have been over and over everything in the cab with the vacuum pump and everthing holds vaccum to 30hg. I even swapped out the vacuum valve. (The vent selector switch) Any ideas out there for the remedy?
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  #2  
Old 06-07-2019, 06:33 PM
CalebJ CalebJ is offline
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Default Re: Vaccum guage

If you cap the engine vacuum supply to the HVAC system and just provide 20" using a vacuum pump, how do the vents behave?
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  #3  
Old 06-08-2019, 04:37 AM
07Vulcan 07Vulcan is offline
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Default Re: Vaccum guage

All the vacuum motors work fine.
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  #4  
Old 06-08-2019, 05:46 AM
tomw0 tomw0 is offline
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Default Re: Vaccum guage

One thing that is easily overlooked is the control head. Inside there is a labyrinth that connects different ports, depending on the mode selected. It can leak enough to make the rest of the part be rather wimpy.
You may be able to take it apart, clean it, lube with light grease, and re-assemble. You may also be able to hear slight seepage of vacuum all the time, engine running.
Does the reservoir retain vacuum for some time after engine shutdown? In theory, you should be able to do a selection or several after shutdown. The reservoir was designed to provide a couple applications of the power brake booster in the case that the engine died, and you needed to stop... Mom would be a bit surprised by the engine shutdown, but even more trying to apply the brakes that were power assisted a few seconds ago, so the reservoir.
You may have slight leakage from multiple spots.
tom
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  #5  
Old 06-08-2019, 09:05 AM
07Vulcan 07Vulcan is offline
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Default Re: Vaccum guage

I did put the vacuum pump on the reservoir and it held vacuum. I looked into disassembling the the vacuum switch, even went to the junkyard bought a used one just to see how difficult of a chore it would be. It is very difficult to take it apart and get it back together correctly. There are springs and tiny ball bearings. I pulled every vacuum line in the cab and under the hood at the salvage yard. Then put the vacuum pump on them one by one harness by harness until all were replaced by passing the vacuum test first. Still defaults to defrost. I wonder if the vacuum motor that defaults to defrost may be leaking off vacuum? I dont know but still on the hunt.
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  #6  
Old 06-08-2019, 03:29 PM
turismolover22 turismolover22 is offline
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Default Re: Vaccum guage

Quote:
Originally Posted by 07Vulcan View Post
What is normal vaccum at the vacuum canister? So far im pulling about 20hg. Still loose ac to the defrost vents. But the vacuum canister helped alot. I can now drive with regular a/c and it not default to the defrost vent. But max air still doesnt work and defaults bad to the defrost vents when it is selected. I cannot find a line broken or leaking any where. I have pulled vacuum with a hand pump and they hold vacuum. I have been over and over everything in the cab with the vacuum pump and everthing holds vaccum to 30hg. I even swapped out the vacuum valve. (The vent selector switch) Any ideas out there for the remedy?
To be honest, this was the same symptom I had in my truck. It was tired as hell with 220k on the clock (01.5 2.3, 5MT) The A/C would work "alright" on normal and default to defrost on MAX.

After the rebuild/refresh, both A/C settings work fine. You could also consider looking into your pulse dampener and IMRC vac lines, if so equipped with the runner controls. Those both were shot on mine, unbeknownst to me, and would cause enough of a vac loss to cause the same symptoms.
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  #7  
Old 06-09-2019, 04:59 AM
tomw0 tomw0 is offline
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Default Re: Vaccum guage

The DEFROST mode is default because it needs no vacuum to work. Take away all vacuum, and it will go to DEFROST.
If you tee in a vacuum gauge, and check the reading at cruise, you may find your engine is more tired than you think. Either you do not produce enough vacuum, or it is being leaked out.
Have you checked the brake booster for leaks(if you have one) or the other lines connected to the 'tree'? You could obtain a bunch of caps, and cap off all the other items so the only thing left is the HVAC.. and see if that makes a difference.
I have to think about it to figure the consequences, but have you checked your PCV valve? It is a port directly to manifold vacuum, that is supposed to be modulated by spring pressure, and seal at the proper time... Gummy could cause problems.
That's all I can think of.
tom
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  #8  
Old 06-09-2019, 07:04 AM
07Vulcan 07Vulcan is offline
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Default Re: Vaccum guage

Thanks Tom. I have checked the brake booster and again no leaks there either. As far as the PCV valve, i havent checked it. But i will next. Thanks fornyour input and advice. I think my motor is is more tired than i think and may not be able to produce enough vacum with 192000 plus miles.
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  #9  
Old 06-10-2019, 10:47 AM
tomw0 tomw0 is offline
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Default Re: Vaccum guage

FWIW, I have seen some engines where the intake manifold is loose... You can rock it up and down a bit... That causes lower than normal vacuum also. If you have tried squirting carb cleaner or other 'fuel' around the intake with no change in idle speed or smooth running, not a likely thing. Worth a look? Yup.
tom
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  #10  
Old 06-11-2019, 01:42 PM
07Vulcan 07Vulcan is offline
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Default Re: Vaccum guage

Ive used three can of carb and choke cleaner. Never once did it change how the engine idles. Ive looked at all the intake gaskets and throttle body gaskets. Still cannot find a leak or hear one. Im gonna hook up the vacuum guage and drive it to see how much vacuum is being lost when under a load. Thats my last thing i think. Other than the smoke machine. Which i dont have. But i have some idea on how to improvise. My wife has a fogger she used at a Halloween party. I just gotta sneak it out to the shop then "modify" it just a little.
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  #11  
Old 06-11-2019, 02:51 PM
turismolover22 turismolover22 is offline
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Default Re: Vaccum guage

Quote:
Originally Posted by 07Vulcan View Post
Ive used three can of carb and choke cleaner. Never once did it change how the engine idles. Ive looked at all the intake gaskets and throttle body gaskets. Still cannot find a leak or hear one. Im gonna hook up the vacuum guage and drive it to see how much vacuum is being lost when under a load. Thats my last thing i think. Other than the smoke machine. Which i dont have. But i have some idea on how to improvise. My wife has a fogger she used at a Halloween party. I just gotta sneak it out to the shop then "modify" it just a little.
look up details on homemade smoke machines. They are really easy to make with a glass jar and some random bits lying about at the house.
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  #12  
Old 06-12-2019, 08:09 AM
CalebJ CalebJ is offline
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Default Re: Vaccum guage

If you're getting 20 inches of vacuum going to the canister, I'm not seeing a problem there. That's a good number and doesn't point to an engine issue.
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  #13  
Old 06-12-2019, 08:50 AM
tomw0 tomw0 is offline
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Default Re: Vaccum guage

there is a youtube showing making a smoke machine from a pickle jar, a Bic pen, a length of tubing, a sock, some baby oil, and a soldering iron. Pretty easy to make, and you can use the cheapest soldering iron you can find.
tom
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