hi,
i have a 94 940 with ac.

1. i have no heat when i dial the mcc switch to heat.
2. i do have heat if i take the vacuum line off the heater valve in the engine bay.
3. i have no heat when i put the vacuum line back on the heater valve.
4. the vacuum registers work (defrost, floor, etc)
5. i don't hear a hissing sound as if i have a vacuum leak.
6. i don't believe i installed it backwards, with the arrow pointing to the heater core.

it appears that my dial switch for heat is not working.

how does this dial operate; how does it relate to the heater valve? it has something to do with the vacuum, i'm sure, but that's the extent of what i know.

the heater valve is the motorcraft yg136, installed 1.5 years ago, no leaks.

thanks,
byron golden
86 245
92 245
94 940

in a 240 there is a vacuum storage tank just to the left of the passenger feet. If it comes unplugged you can loose Vacuum.
In a 740 I found it inside the front bumper. not where you'd think to look, so you might look for the line to that little plastic tank, If it leaks it might cause similar issues. I didn't even know it was there until I happened to remove a front bumper.

hi phil,
the 240 vacuum tank is behind the central console and it can slide out horizontally.

jay, the 240 vac tank is white. it has the appearance of 3 globules melded together. vacuum ports are on either end.

hope you have a snow blower with plenty of gas for this weekend.

regards,
byron golden

Dear bcg,

Hope you're well and stay so. I asked about the color of the vacuum tank, as I thought amazonphil had confused it with the fuel system's vapor capture canister, a black plastic item hear the front bumper. Indeed he did so.

All the best for the Holidays and for 2023!

Yours faithfully,

jesecon

Hi,

What did you find out about the electronic gadget, on how or if, it bleeds air towards the heater valve? It’s should fail open to full heat in a non energized state.
A vacuum is not a normal state in the universe, unless you’re in outer space part.

Seeing some of this new engineering means it’s probably done in some other complex way so they can work for NASA.
Where was your redundant system?
Whoops, no backup procedure in the manuals either?
Are you always able to roll a window down, except when their electric. Whoops!

Have you checked for dirt in the orifice or orifices?
It Might be as simple as that.

Does it look like it controls a solenoid valve by pluses, rather than just open and shut it off, like a EGR controller valve? The valve on that, under the hood of 240s gets plugged up every few years too.

Seems to be another case of backwardness, like the 240’s overdrive lock out solenoid on the automatic transmission.

Me thinking, just how many years and the numbers of vehicles have been built?
And we still have those simple issues hitting us, but then again, there’s the bad windshield wiper.
(:-)

Phil

Dear Amazonphil,

Hope you're well and stay so.

What is the color of the plastic tank, to which you refer?

Thanks in advance!

Yours faithfully,

Spook

it's black and fitted inside the front bumper of my 740. i think it was either in the middle or towards the driver side.

4 bolts and you can remove the bumper. You can pull the shock with the bumper or unbolt it from the bumper. there may also be some side trim so if it wraps around and is connected to the fender as well there might be some bolts uniting that corner. I would not remove the trim from the fender, but unbolt it.


if you can access the hose I'd just suck on the hose and see if you can make vacuum . you could tee it to the manifold and put a vacuum gauge on it.

If it doesn't; leak then it probably isn't that, but might just be the rubber hose came off.

the rubber servo things seem pretty robust. I took apart my airboxes and set them aside when I disassembled the car and some were quite well buried inside those plastic housings. the heater core itself seemed to require a lot of dashboard removal etc It's right behind the firewall and buried up there in plastic. you cna see the hoses in the engine bay.

near the radio where that slider thing lives you can likely get to the ends of every hose there and I think you can test them by applying vacuum to each hose.

I would not go trying to disassemble more than the area around the valve unless you find a non functional one. perhaps it is leaking at the slider valve assembly.


each hose simply leads to a diaphram. there is a return spring at the diaphram.

someone struggling with a heater fan motor replacement or a radio might have accidentally unplugged one of those hoses.

in my 740 I found that the heater fan motor was full of water, not only that but it had a plastic container built around it and it was full of water. I dont know the cause but perhaps there is some plastic just below the vents on the outside of the car below the windshield, they shelter some things and if cracked maybe the water leaks from there. i removed the whole dish shaped plastic near the heater fan. it still blows but I dont think it blows as well as it did wit that plastic thing in place. I removed it because it was causing water to stay all around the motor and the motor was completely submersed. I think I took the motor apart and saved it but it was full of rusty water. with that plastic removed I did not get any water on the floor so who knows why it was filling up in there?

the 240's are horrible for access to the heater fan. If you need to do one of those Id remove the seats and plan for a whole weekend of knuckle scratching and cursing fun. on a 740 it's much easier.

I have a tool that looks like a big metal syringe and it was intended for bleeding brakes. I did not find it worked so well for brake bleeding but a tool like that might work for testing.

I got a hold of a vacuum generator and I connected that to a pressure cooker so I use that for brake bleeding.

a vacuum generator is a thing that hooks up to your compressor and then the air from your compressor blows through it creating vacuum by way of a venturi. they are very simple, no moving parts. one problem with a vacuum generator is the air rushing is quite loud and you may want to be listening for if you can hear the flap move or not. you might consider putting a Tee near the connection to the manifold for the fuel regulator and then obtain test vacuum with the engine running. you could use one but I'd put it and your compressor in a different room so you can hear better. you can get quiet little vacuum pumps.



if you can run the heater fan and then actuate the vacuum servo by way of a vacuum pump or something then you might be able to see if it's doing it's job of redirecting the "flow of vacuum"

.. even vacuum in the manifold isn't really actually vacuum because we are all living and working under atmospheric air pressure but lets ignore that bit of science and think of it simply as "vacuum" even though it would be more correct to talk about pressure differential. thinking deeply about vacuum from that scientific sense probably just adds unnecessary confusion.


the rubber servo thign is like a bellows, when vacuum is applied it shortens the rod length, a spring pulls it back. I'm not sure which way they fail. Ive never seen one fail. if you suck on the hose it might move, If you blow into the hose it should not leak. don't hook compressed air to it as that could blow a line off somewhere where you can't reach.



those vacuum hoses of course dont really want to fall off because the vacuum is pulling them on and together, the lines don't contain any pressure. one may be rotten sure, but I think the likely cause is that someone was working inside the dash and inadvertently pulled a hose off and if it was summer they may not have noticed. In winter you need those things to work or you can't see where you are going, so they tend to suddenly become really important.

if you get to taking the cigarette lighter and console apart , I seem to recall fighting to remove the plastic that houses the lighter socket. eventually I looked closer and found a little piece of black plastic that unclips and reveals a screw. If you get there and seem to be struggling get a flashlight and have a look it wasn't very evident to me how it comes out until I found that plastic cover thing right near the lighter. Its easy to break it out of frustration if you don't find the quite well hidden screw

the sides of that center console thing had bolts from the inside , near the fuse tray, they were hard to access. I think Id' try to take those sides right off to see the hoses better. You may find something wrong with the control, maybe it leaks.

you will find a few small bulbs that light the ashtray and other bits in that area. they also light up the shifter so you can see what gear you are in. If you can lay your hands on a few of those bulbs you might replace any bad ones. there is one for the rear ashtray . they are little bulbs that I've never seen used in other cars and half of them are likely blown. If you visit a wrecker you might think of taking a few.

I think I have the heat control and some servos if you need But I am Near Vancouver Canada. If I have them they are all from an 88 740 sedan.
the 240 had pushbuttons for vacuum control and the 740 wen to that slider thing. I bet that if you can get to the hoses you could use a 240 one although it wouldn't fit the dash, its a bit more simple perhaps? maybe using one from a 240 could be a quick fix if you are stuck.


If you remove the speedometer I'd look for a reset button thing. I think they had it so it would reset and light an engine service dashboard lamp when the timing belt is due. it was so that the owner would then go to his dealer questioning why it came on and the dealer would tell him his timing belt is due.

probably most can replace the timing belt but may not reset that thing so it's good to reset it if the speedo is ever removed. I'm not sure if every model used that thing, 240's did , maybe 740, not sure about others. I think you can actually reach it without removal of the speedo if you know where it is. That can save questioning why the silly idiot light came on. Its supposed to come on at every 50 K or some other mileage setpoint. a new belt usually comes with a sticker so you can put that sticker on the timing belt housing and write the mileage down there instead. I think the idiot light "feature" will mainly confuse people unless you are bound to a dealer.



I have a friend with a dodge charger, It must be around 2011 or something, which I consider "new"

those cars have ridiculously cheap little made in china plastic motorized gearboxes to control the heat flaps and the gears inside are designed to crumble and fail due to plastic breakdown after about 10 years. what happens if the teeth fall off and then they dont move or they go click click click for a while, as the missing teeth skip by, until it self destructs and it was engineered to do. people think they are " buying American" but the cars still fail just as they were planned to , due to this sort of garbage which is definitely easily predictable at the factory level.

Volvo's system of using vacuum was quite simple and they really didn't fail very often back when volvo was made with quality and longevity in mind.

I find it sad what happened to the Auto industry, it definitely wasn't "green" to make everything with such quickly planned obsolescence.

Dear Amazonphil,

Hope you're well and stay. The black plastic canister mounted just behind the front bumper is part of the fuel vapor recovery system. It has nothing to do with climate control.

I once changed a heater blower motor on a 240 wagon. Book-time - if I recall correctly - was nine hours. I didn't have the book: took me 13 hours. I hope never again to do that job.

On 740s and 940s, there's a drain hose that leads from the heater fan enclosure to an opening in the firearm. The drain hose sometimes gets clogged, so water pools in/around the heater blower motor.

To clear the drain hose, take a piece of lightweight coat-hanger wire, and bend the wire at one end, so that the tip is doubled. Polish the area with fine sandpaper. Push the polished end up the drain hose end. You may have to try several times, to penetrate the clog. Go gently. You'll know you've cleared the clog when water trickles out of the hose end.

Hope this helps.

Happy Holidays and All the Best for a Good, Healthy and Boring 2023.

Yours faithfully,

Spook

The charcoal cannister is int he engine bay near the airbox with three hoses . but this Vacuum reservoir is inside the front bumper. its an oblong shape , made to fit in there.

here is an ebay ad that shows it

https://www.ebay.com/itm/173087411628
if the link fails , try searching the part number 1395893 L16

I think it i very unlikely this vacuum tank will ever fail but it might come unplugged from the hose. If that came unplugged I think the heat controls would stop working. if it were loose or cracked maybe they would work but only sort of, due to the leak.

It' very well protected being inside the bumper and probably the least likely part on the car to ever actually fail.

I suspect that a hose fell off somewhere , or it may be a problem with the control valve located in the dash behind the heat controls.

there might be some different part numbers , depending if it has AC or no AC.

this thread might have some more info in it
https://volvoforums.com/forum/volvo-240-740-940-12/740-wagon-ac-vents-not-working-83573/

Dear amazonphil,

Hope you're well and stay so. Thank you for providing the part number!

I sit corrected. According to Volvo VADIS - a superseded dealer parts/service database - Part #1395893 is unique to Volvo 740s (up to and including the 1989 models). It indeed is a vacuum reservoir for the climate control system.

I suspect the long run of tubing created the risks you mention, so the vacuum reservoir was moved closer to the climate control unit.

All the best for the Holidays and a Good and Healthy 2023!

Yours faithfully,

Spook

Hi Spook,

I'm not familiar with a vaccuum reservoir being behind the front bumper area in our RWDs. I'm not sure where that ebay recycler got those fitments as being for a B230F. The part you refer to 1395893 is listed on Volvo parts sites as being for the 780s with B280F and some late 1980s European 240s (B200ET), but not 700's in general nor 900s. I suspect the ebay listing is a typo as those are the B280F years that are listed

For 740s and 940s, the vacuum reservoir moved to the centre console, at the base of the evaporator core area. It's a fairly plain round ended tank shape, unlike the 240 four tennis balls in a row reservoir tucked up at the back of the centre console behind the glove box side. I see two different p/n's for the 940 reservoir: 3522370 for the earlier one and 6841037 for the later '94-'95 940s, but they look identical to me in the parts diagrams and I have no idea why they would need to be different. To my knowledge they are not known for leaking and you would have to be doing some serious disturbance around the air distribution box to pull the hose off. 940 air distribution systems are instead well known for the diaphragms leaking in the three vent actuators on the left side of the air distribution box. Each actuator is on a separate vaccuum line from the heater control unit and loss of vaccuum for one actuator can affect the whole vaccum system when the vent control is in that position. Loss of vaccuum at multiple actuators could cause significant loss to the point that the heater valve no longer responds.

I'm wondering if someone like a PO may have tried using something like RTV to seal the rubber hose connector at the heater valve. Pushing the line into the rubber sleeve could foul the end of the line. If during later work a piece got on the end of the vaccuum line it could easily get sucked into the line and cause a blockage. Poking a wire in to loosen it might drive it further in.

Best of the season to you -Dave

[p/n 3522370 & p/n 6841037 #20 below]


--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Dear Dave Stevens,

Hope you're well and stay so! I agree: on 940s, the vacuum reservoir is mounted as you state. Sometimes parts identical in appearance/function come from different makers and so are assigned different part numbers.

As to 740s, I don't spend time on them, as I don't own one.

All the best for the Holidays and a Good and Healthy 2023!

Yours faithfully,

Spook

i replaced the ac-heater control module with one found in a junkyard. luckily, the unit was serviced, repaired by programa some years back.

the unit reduces the vacuum to the heater valve as designed, now.

previously when i turned the dial for heat, the unit maintained vacuum on the heater valve, keeping it closed. no hot fluid went to the heater core.

i'm slowly taking the original unit apart to see if i can repair it.

thanks for all the help.

regards,
byron golden

Hi all,

I’m just reading on inside this and really know nothing about this series of cars but would like to throw this out there.
It has been my belief that automotive heater valves are suppose to fail in heating mode for safety reasons.
This is to keep someone from freezing in cold climates despite
This provision was to be provided in regulations of my year cars. Especially, if not controlled physically by a mechanical means or any said has can be overridden to provide heat.


I was going to post the above way earlier but was having trouble with 403 error codes.
I didn’t remember if I had saved it before that hit me but apparently I had.
This might explain how the heating control apparatus controls the heater valve.

Phil

hi,
normally, i look up the names so i can address you with your own name.

anyway, yes. if you can find that information, that will help me to troubleshoot the problem and report back.

funny, the vacuum remained while i dialed to heat, which should reduce the vacuum to open the valve for heat.

i'd rather try to fix the unit and have a spare than to spend lots of money on a replacement.

thanks!
byron golden

Hi Byron,

It is a nice thought to remember names but mine is “Phil” almost like dirt in a hole. (:)
Not as “uncle Phil” as “Kittysgreyvolvo” has called me occasionally.
He is good for distorting words in his posts to have fun with all of us. (:)

As far as me having information on what I said about things being done to have things “fail safely,” I don’t.
You only have to be observant. They are around you all the time.
Take for instance an traffic intersection with automated lights.
They have a default when a failure occurs.
The lights will flash red in all directions of control when there is a problem.
This mode puts the intersection under “manual control” for those using the intersection.
Everyone is required to stop completely and basic operational driving rules apply.

In your case the valve was made to “fail open” to full heat without any outside energy applied to it.
It’s called “at rest” position. “Normal” this or that?
If a valve is put into position opposite, of what is was used there for, it is “tagged” with “Not Normal.”
SAFETY starts with communications and forethought.

In this case if controlling vacuum line broke or split you would have full heat.
If excessive moisture, say frozen water vapor, got into the system and plugged the line from getting vacuum, you would get heat.
That is, providing some air leaked into the line over a period of time and that does happen more than you think. The reason for vacuum reservoirs.
In your case, no vented air came in and vacuum was allowed access to the valve all the time. Controller failure.

In the case of your controlling valve, it either bleeds air in or restricts the vacuum source.
It’s not a fail safe valve as it is designed to be a “variable function” valve.
In other words, it’s upwards from the “safety” fail safe operation and “ultimately” cannot be defaulted one way or the other. It’s a middleman controller.

Upon failure, you become the other working middleman.(:)
If it failed to full heat you have to adjust the fan speed, go to recirculating mode or just roll down the windows! It still fails safe.
Since you failed on the colder side you came to the BRICKBOARD. (:) Now that’s cool alright! (:)

You will have to find, on the old valve to be repaired, how it lets air in towards the valve to release its holding power. It’s probably through and orifice or the physical limitations of the valve itself.

The EGR valves on the 240 and most other cars “fail closed” to insure that the exhaust gases cannot continually be held open.
It is operating itself electrically from the ECU through a solenoid valve that applies vacuum to open the valve per a program in the ECU.
When the valves open it heats up a sensor that the ECU monitors.
It starts looking for a change of state or status from where it was when it sent a signal to open.
It needs to see this in a predetermined time frame or it turns on a CEL and records an emissions code.

Now, what I have found, a couple times, is the valve get plugged up or sticks from debris. Each time the EGR valve has been fine.
The solenoid gets into the same predicament as your manual valve.
This is from your side with a knob or automatically from a sensor controlling it remotely. Automatic climate controls now that is another ball of ugly wax!

Either way it cannot pass vacuum or let air in to the EGR diaphragm.
This solenoid valve has a foam filter on its top under a cap. The foam can deteriorate into dust or let’s dirt get in for ventilation.
I get my valves cleared with some denatured alcohol and replace the foam with polyester fiber.

You are going to be looking for the same kind of scenarios.
You may not have to open anything up and you may not be able too?
Just rinse the insides with an alcohol.
I favor denatured as it less of “other things” in it that isopropyl can have.
Either will work to do a light flush through it.

You might consider a fine or light spray of a “dry type” of silicone spray, for any seals, after cleaning.
If it had anything in there from the factory, it was a very light weight film of oil and probably has evaporated.
Maybe, it will help pass any future incoming debris.

Yep, tinkering with an old valve can teach you things.
Since it doesn’t work correctly what you can you lose.
It can do one last thing for you … treat you to some knowledge and experience.
Glad to see that you want to be curious!

Phil

Dear bcg,

Hope you're well! Thank you, for posting the results of your research. I don't recall a post reporting a failure of the temperature-level selector switch, so your work is most helpful.

Yours faithfully,

Spook

Hi Spook,

I do recall discussion here way, way back, of a failed heater control panel. A hissing sound was traced back to behind the panel. I expect it would have been the vent control rather than the temp control. It's certainly not common. I expect a number of heater control panels have been unnecessarily replaced where the leak was actually a diaphragm in one of the vent actuators on the central distribution box, a much more common problem. Last time I had a heater control panel out they do not at all look serviceable.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

hi jay,
thanks for the kind words.

i conducted a thorough search scouring the internet and brickboard for a couple of days. nothing!

currently, i'm disassembling the unit and trying to find where the problem(s) lie. if i find anything, certainly i'll post it.

first, i thought it may have been the potentiometer, but malfunctioning unit has the same resistance as the working unit.

i have the back of the selector switch off and it looks like that's where the vacuum operates. i haven't found any anomalies, yet.

it's nice to know that i could send in my unit to programa, if i had to, ~$150 to fix or replace.

thanks,
byron golden

thanks for your replies bill and dave.

i'm thinking the problem has something to do with the heater servo motor, p/n 3522797. i don't know if it is not working or the cold-hot dial has issues. i'll need look further.

i did take the glove box out, recently. maybe, i pulled something off, a pigtail, perhaps.

the heater valve is not installed backwards. when i have vacuum, the ac is cold. when i take the vacuum off the heater valve, heat comes out.

so, it appears that i'm not able to vary the heat. that reduces to either the servo motor not working or the dial is not working.

again, i'm not sure how the dial operates. does it reduce the vacuum when turned to heat resulting in the valve opening? does it operate a flap/ blender? both?

i can work out a solution if i know how the the cold-heat dial operates.

thanks

Hi Byron,

What's your e-mail, I'll send you two heater files.

Bill

hi bill,
byron.golden@gmail.com

btw, i have the volvo parts manuals. of course, they don't say anything about the function.

Thanks,
byron

The flow arrow on the heater valve is supposed to point to the firewall, the hose to the lower intake nipple for the heater core. The outlet hose on the upper core nipple goes to the red metal water pump return line along the far side of the block, so that sets the flow direction.

Your description suggests the heater valve is normally open if you're getting heat with the vacuum hose disconnected. On a few cars the heater valve is normally open, but on most cars like our 700/900s it's normally closed. Your Yg16 valve has been working for you up until now, so that would suggest it's the correct valve and having it the wrong way around is behind this.

So why is this happening? If anything, if the valve is normally closed, you'd think there would be no heat no matter which way the valve was installed and still no heat when connected unless the heater control was set to ask for heat and also able to successfully provide vacuum.

So here's what I'm fairly sure is happening. You will notice looking inside that the valve seats at an angle and thus will want to open when fluid is flowing in the wrong direction (opposite of being held shut when connected the other way as it's supposed to be). With the hose off, air can freely come and go from the diaphragm chamber allowing the valve to open. When the vacuum hose is now connected and the valve tries to open with flow, the valve is held shut because air can no longer freely move in/out of the diaphragm chamber.

I'm guessing simply turning your valve around will fix it.

If after this you're still having heat control issues then that would suggest there is a possibly minor vacuum leak somewhere, such as at the heater control or heater valve as long as you've carefully inspected the vacuum hose for kinks (especially near the valve, but also under the dash) and for leaks/split at the rubber coupling sleeve connecting it to the heater valve. With age, that rubber sleeve takes on a slightly different inlet and outlet diameter so double check it's also the right way around and sealing. I'll use a tiny zip tie on it if it doen't fit snuggly on some of the aftermarket heater valves like the ProParts one that's similar to the revised all black plastic Volvo design. Another trick I've done with the ProParts valves is to trun the sleeve wrong way around so it seals to the valve nipply and simply shove the vacuum line in a little further, often adding a drop of RTV to hold it there. See the FAQ for more information on MCC heat control vacuum leaks.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hi Byron,

Checking the 900 Heater FAQ (no heat):
Here's something to check.

"Your firewall-side heater water valve was installed backwards; The arrow on the valve points to towards the firewall inlet, not back towards the engine."

Someone with more experience than me can confirm that soon.
Download the comprehensive 900 FAQ to help you solve your issue.

https://www.brickboard.com/FAQ/700-900/

Good luck, Bill