Detailed info on Vacuum leak

J

jobear

Registered
I received some great info from Mr John and Driller regarding a vacuum leak affecting the air conditioning. All good info and something all should read but I need to go into more detail. The preoblem appears in only warm weather if that is possible. I had it to the dealer yesterday and they had it all day and could find nothing wrong. It would not default to the defrost mode. The dealer is at the beach area and yesterday it was overcast all day and about 70 degrees or so. After leaving the dealer I drove about 75 miles home, everything worked just fine. I live in the desert area and it has been 85 with a couple of hundred degree days here. Today I went to work and it worked all the way there and the temperature outside was about 70. When I got off work the temperature was close to 85. The air immediately defaulted to defrost. Anyway, point that I am trying to make is that the check valve has been replaced and the problem still exists. Although still only 90% of the time, as before. Obviously in the warm weather everything expands. What can I look for as the dealers seem to be no smarter than I, lol. At least if I had something to suggest they check for.
thanks so much,
Barry
 
RE: Detailed info on Vacuum leak

The ambient temperature change may be the missing clue.

Mr John's description of how the A/c system maintains vacuum while its source (manifold vacuum) rises and falls with engine load is excellent. If you understand it, you'll obviously understand the need for the tank/reservoir in the passenger fender to be 100% airtight if it is to hold vacuum for the heater controls to maintain settings during low intake vacuum situations.

This is not always the case, though.

I have seen a number of these tanks, on various Ford products, develop leaks in their seams where they are plastic-welded together. When the plastic of the tank is cold(er) it is contracted and sealed. When the temperature is high enough, expansion allows small leaks to become evident.

You could pull your plastic inner fender down to gain access, remove the tank, examine it carefully for cracks, seam splits, or holes and replace it or seal any imperfections with epoxy.

OR:

You could also diagnose it for leaks with a vacuum gauge and tee.

First, remove the line that goes to the reservoir from the valve Mr. John described. Using a couple of other pieces of vacuum line and a tee, tap into that line with a vacuum gauge.
Start the engine.
You should now see the gauge slowly climb (as the tank evacuates) to a good manifold vacuum reading, ~17-21".
Assuming the valve is working correctly, this vacuum reading will remain constant even if you goose the throttle. This is the reserve source for your heater controls in action.

Now for the real test:

Shut the engine off.
Again,assuming the valve is working correctly, your vacuum reading should stay where it is for quite a while, in theory forever.
If the reading drops in a matter of seconds, you have a leak.
Look for it.
Keep in mind, at this point, the leak may also be in the line from your tee back to the tank. Look for small cracks in it before condemning the tank. These plastic vacuum lines get very brittle with time.

One further caveat: you may have a leak somewhere under the dash that is consuming the vacuum at a greater volume than the tank is capable of holding, but that's fairly rare.

Let's investigate the valve/line/reservoir area thoroughly for now.
 
RE: Detailed info on Vacuum leak

Frankie,
man, what a really great response. I have been through hell trying to get someone smart enough to know all this to work on it. Maybe I need a vacation and could come up there, lol. thanks again for the advice and I'll try this one next. It is kinda cool to take the car into a dealer with printed instructions, lol.
Thanks again and I'll post the outcome in a week or so. Or I'll
email you with the results. The darn thing seems to be working more than not these days. It worked all day today except leaving Costco it didn't work for a few miles and then was fine again.
Chat soon and thanks
 
RE: Detailed info on Vacuum leak

One more question Frankie X,
The check valve in my '98 is a two port-one in and one out-
manual calls for a three port as far as I can tell. Which is correct?
 
RE: Detailed info on Vacuum leak

You've put me on the spot. I'm not sure about the valve. I'll sort it out with my parts guys on Monday.

I'm becoming more concerned with the fact that the system works correctly more often than not. I have NEVER seen one of these check valves work intermittantly; when the inner valving stops sealing, the valve is Kaput. Period.

Still, I'll stand 100% behind Mr. John's information. It's certainly the path I would have chosen, and, based on your initial description of the problem, I didn't bother to post anything because the situation seemed well in hand. Default to defrost is almost always the check valve.

...except in your case, apparently...

Let's follow the vacuum leak path for a moment. There's two routes: either the tank cannot hold enough vacuum to maintain HVAC door positions (that's my previous post), or there's a leak under the dash large enough to vent away the reservoir too quickly.

The ambient air temperature clue is something I'd like to investigate a bit further.

In an automatic climate control system, in high temperatures, the recirculation door is used more frequently to keep cabin temperatures lower, rather than trying to cool very hot outside air. If you have a leak in the lines from the back of the control head to the recirculation door vacuum motor, or in the motor itself, your defrost default would occur while recirc. is demanded.

Try an experiment when the A/C system is working correctly: switch to Max A/C (this is nothing more than manual control of recirculation) and see if your problem begins. If it does, you'll know where to start looking.

...which reminds me... at no point have you told us if your default is more frequent in certain HVAC temperature or position settings than others.

Is it???
 
RE: Detailed info on Vacuum leak

I think the leak/bad connection is behind the dash, Frankie. I thought I read somewhere that Barry had something done to the blend door.
 
RE: Detailed info on Vacuum leak

I agree.

I'm trying to cover all the bases, but if I were to make one long distance GUESS, it would be that the recirculation motor line is cut or dangling loose under the dash!
 
RE: Detailed info on Vacuum leak

thanks again for more info--
Blend door WAS replaced---
I never use it on max as it is very cold since I had it bled and recharged. usually set fron 72 - 75 degrees.
I have a problem, when I try to warm it up a bit inside if the air is too cold, and set it at 77 degrees it is still blowing really cold air, lol. I can adjust the blower of course at any time but at 77 I would think the air wouldn't be quite as cold. Maybe that is a clue a well. It is still intermittent and usually after a while it works just fine. sounds like the tank but you guys are they experts.
It always works well on vent/floor but did default one day to defrost from there but usually never. Thanks again and a reply to this would be greatly appreciated.
Barry
 
RE: Detailed info on Vacuum leak

I think you've missed the point of my earlier post.

In order to narrow down the leak possibilities, when the system seems to be working well, I want you to DELIBERATELY SELECT MAX A/C to see if that position triggers the default. Let us know what happens.

You haven't really helped in your description of the second, previously never mentioned, problem. Do you have NO control over temperature? Will it get warmer if you dial up temperatures above 77?

If you have no control at all, that's a blend door or control head problem.

If you have to just dail up a little higher than you think you should, that's probably a cabin temperature sensor problem.

You're really not giving us enough information to allow any of us to get to a root cause. Don't just say you don't use MAX because it's too cold. Use it! Use every position and every temperature setting. See if any of them seem to trigger the default. Look for any pattern that might help us help you!
 
RE: Detailed info on Vacuum leak

Frankie, I will try max tomorrow and I'm quite sure that once the defaualt stops it's thing, the auto continues to work, but will post after I try it tomorrow. When I change the temp, the blower slows down but I don't think the temp warms. Also never had it above 77 so not sure about that but will check that out also and hopefully give you some accurate details. I understand what you are asking and will try to give better info. After a few miles it seems to work properly on automatic as far as the blower goes. I will get you an update on the temp control and max details tomorrow. Thanks a lot. You have been extremely helpful so far.
Barry
 
RE: Detailed info on Vacuum leak

Hey Frankie,
Paid great attention to detail today. Hope it helps.
Outside temp 83 degrees when I left work. Turned air unit to "auto" and then I idled through the parking lot and the first and second time I accelerated out on the street it defauted to defrost. After that it worked just fine on auto. When switched to max it would default to defrost. After complete engine warm up it would still default to defrost on "max". I travel up a failrly medium grade going home after about five miles from work and the unit always worked just fine on "auto" today. Everytime I switched to "max" it would default to defrost. When it would default to defrost I would switch to "auto" and it would not return to normal operation until I took the load off the engine by letting off the gas completely or go into a small down grade.
The temp did adjust properly today. When I would click it up to 79 or 80 it would stop coming through the vents and I believe go to the floor. When I hit the vent/floor button it would come through the vents warm, so I am assuming that is working ok.
Hope this gives you the right answers you were looking for and I GREATLY appreciate this interest in my problem. If you want to speak to me, email me your number.
thanks again, Barry
Barry
 
RE: Detailed info on Vacuum leak

Frankie - have him do a self diagnostic to see what that reveals. (I don't have my books here). I don't think it is related to the blend door. That's electric and is monitored electrically. Also, I think your assessment of a leak in a vacuum tank could be part of the problem since the temperature outside seems to affect it, but it would have to be one hell of a hole that opens up then closes. It sounds like the whole control assembly needs to be replaced. A cut hose would not do this, but maybe the connection between the plastic tubing and the rubber adapter could leak enough???? I still think it's the control. Maybe the self-test will show something. Maybe a vacuum motor is bad and is allowing the vacuum to leak from the tank. Do what Frankie said and try each position of the heating A/C system manually. When you find a vacuum motor that is bad, it will let the vacuum out and default to the defrost mode. Make sure you leave enough room out to empty the tank. In fact, start the car with the heat A/C in OFF and go through each setting and listen for a leak that does not stop. The vacuum motors should complete their motions in 2 to 4 seconds (max). Don't forget to turn the system back off and start and run the car after each button press to build up vacuum in the tank. If the outside/recycle motor is bad, it will drain the vacuum tank completely when the system is in OFF mode. So, check that first.

For the person who was talking about a 2 port vacuum valve. They are used in a vacuum system, mostly a pollution control system where the vacuum needs to be supplied at all times, regardless of the accelerator position. These sometimes also have a small diameter hole that lets the vacuum out at a predeturmined level when the vehicle is off or the vacuum is not on the specific hose to the device directly. Also sometimes the vacuum check valve is built right into the vacuum tank. This would also leave you with 2 connections.
 
RE: Detailed info on Vacuum leak

Right on the money!

One note, though, Barry: as you experiment with positions, you'll probably have to drive the car and accelerate to lower the manifold vacuum and duplicate your symptoms.

Unless the leak we're looking for is HUGE, just idling may keep manifold vacuum high enough to overcome it and hide it.

I'm most inclined to suspect the recirculation door motor or line.

Mr. John has brought up another valid possibility: I might be partially correct and it's the recirculation circuit internal in the control head itself.

Still, if you consider that work was recently done behind the dash, I'd be more willing to believe something was damaged or left unplugged before I'd believe a totally coincidental heater control head failure.
 
RE: Detailed info on Vacuum leak

thanks guys, both of you-
I have experimented with all postions and have narrowed it down to a default to defrost on start up or warm up on "auto" for a block or two and then "auto" works well for the rest of the day, and on Max it always defaults,--- always. I can get this to happen just sitting still with accelerator and brake on and putting on a load of sorts. Even very small inclines and a small load while driving make this happen.
Am I to understand that I can hear the vacuum build and shut off? Also what will the leak sound like and where will it come from. LF fender area?
Also if I take it to a dealer, as I am not extrermely mechanical myself, am I to suggest he check in the dash area? Where would you start if I was lucky enough to come to you in Ontario, or to visit John?
Also John-- I mentioned that the car currently has a two port valve -a one in & one out valve and the manual calls for a three port valve for this car, they have told me. The current valve appears to be a good one but it was just mentioned as information.
I don't completly understand the test directions but am rereading them again.
One more item that may or may not help. Today the outside temp was 88 and I did adjust the temp to 83 (on auto) and it kept us quite comfy. I thought that was set a little high to be putting out cool air.
You guys are the greatest and I feel we are so close that I just need a little bit more info to understand what to ask the tech down here to zone in on.
thanks so much ,
Barry
 
RE: Detailed info on Vacuum leak

Thank you, Barry! That's exactly what I wanted and expected to hear!

If it always defaults on MAX, I know my theory is correct. I'll say it again, because this is what you'll tell the service department:

It's not just "behind the dash". The leak is definitely in the vacuum circuit to the recirculation door. Tell them MAX position always triggers the default.

If the boys at this shop need more information than that, they're just parts replacers. Take your keys back from them and go somewhere else!!

It makes me very sad to say it, but all dealership techs are not created equal.

I'm hoping for the best for you.
 
RE: Detailed info on Vacuum leak

Thank you once again, I now have a place to start.
If you ever need any interior upholstery or moonroof questions or advice just give me a holler--I did that all my life - same goes to John and Schultz and anyone else in need or that helped sort this out.
thanks again,
 
RE: Detailed info on Vacuum leak

If you have a 2 port check valve, you simply have got the wrong valve. There should be a 3 port valve on every Mark VIII. I have the SM for every year vehicle and it shows a 3 port valve - 1 port on the large round section ans 2 ports on the smaller round section that is mounted 90 degrees on the other side of the large round section.

If you send me your email address, I will send you a picture of the valve and how it's supposed to be connected.

The engine vacuum is connected to the large round section's port and then the vacuum tank and the heater A/C is connected to the other 2 connections. If you have a 2 port check valve, there is something wrong. How is that valve connected?
My test was to start the car with the heater or ETAC in the OFF position and start the car for a short time to fill the vacuum tank, then turn the key off. See if you can hear any vacuum leaking. If there is, try to find out where. If there is none, press the defrost button, listen for a leak. You should hear nothing because this is the default position. If you don't hear one go to vent. You should hear the vacuum moving around for about 2 to 4 seconds. If it stops then start the car back up and run it for a minute and stop it again. Listen for a leak. If you don't hear one, continue all the way through each button starting and stopping the car until you hear a leak. You should hear vacuum moving each time you change buttons, but the vacuum should stop after 2 to 4 seconds. If it continues past that point, you have found either a leak in the hose to that vacuum motor, or that vacuum motor is bad.
But if you have the wrong check valve, that's your problem.
 
RE: Detailed info on Vacuum leak

Hey John,--thanks for all the info -- between all of you guys help I think I have a handle on it and at least know how to direct the tech if I can't fix it myself, which is doubtful, lol.
Thanks for the offer for the picture. Just go to one of my posts on this subject and on the left their will be an email envelope. Hit that to sent me an email.
thanks again,
Barry
 
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