Hissing VEM!

[jamescarruthers]

I have a problem with my VEM on my non-air-con 1987 480ES.

The air direction buttons produce a hiss noise (escaping air) and no change of direction in air except for the windscreen/defrost button, which is the only button that does as it should.

Luckily I have a spare which I am going to swap over at the weekend but I wonder if anyone else has had this problem. I did wonder if there was maybe a leak elsewhere or a pipe off. I haven't managed to find the source of the hiss noise-- although haven't tried too hard.

I think air-con cars have exactly the same air distribution system with the push buttons.


Thanks in advance,

James

[Ben Harris]

I seem to remember (from many years ago!) that there is a vacuum line which run behind the VEM, and is used for repositioning the vents. I'm guessing that the 20+ year-old rubber connections will have perished and need replacing. If you're going to the effort of removing it entirely to replace it, then I'd have thought it will be obvious one it's out.

Ben.

[jamescarruthers]

Thanks Ben, I'll get it out next week and report back.

[gsa60]

Hi James.
I had the same issue about a month ago. In my case it was the VEM that was at fault. One of those solenoids that redirect the vacuum was leaking.
I ended to swap the VEM as mine had the fan tracks burnt also.
Cheers

[jamescarruthers]

Repaired!

There were some missing O-ring seals on the vacuum outputs internally, hence the hissing.

Also, one on the pipes was crushed so I managed to get a replacement set from the scrapyard.

I did discover some burnt bits on the PCB so I'm looking for a replacement VEM, importantly from the earlier cars with a green l/h plug/socket.
See here: http://www.volvo-480-europe.org/forum/v ... =8&t=34461

The seals obviously fell out on somebody's previous investigation of the burnt bits!

[Flying Dutchman]

I've got a similar problem on my 1990 with AC. The VEM wont change directions no matter which button I press. Otherwise all the buttons and LEDs work as they are supposed to. Mine dont make any hissing sounds but I can hear the relays click when i push the little buggars! Any suggestion what to start with?

[jamescarruthers]

There aren't relays but push button air control valves.

If you have no hiss, then maybe there is no air (or is it vacuum, I can't remember?) feeding the VEM unit. The feed air pipe goes across to the R/H side of the car (driver's side in the UK) behind the dashboard, I'd check that first. If you get in the footwell you'll be able to spot it, going out into the wing.

Be careful taking the pipes off. They're pretty tough but the ends loop over the unions of whatever they attach to so you can't just pull them off. Basically, try and see an easy one first before you try and take one off blind!

[Flying Dutchman]

Think its vacuum. Is it fed from the intake manifold? There s 3 lines connected that goes into the RH fender

(why 3 ?)

Maybe one are broken, cant hear any hiss, but thats hard of course with the engine running.
Will have to examine further. What do you think about the possibility of the VEM being broken?

[jamescarruthers]

I think only one exits the car (to the vacuum) and the rest go to vacuum servos to move various parts of the ventilation system. I'll dig out my book when I get home and take a picture of the schematic for you.

[Flying Dutchman]

Thanks! That would be great. I actually read about the sama fault as I, in a thread on the swedish 480 forum. Solved by changing the VEM since it is irreparable.

[jamescarruthers]

It could be repairable. I took mine apart and found that someone had previously took it apart but lost all the seals! Also, if you've got no vacuum going in (pull it off and listen to the input pipe) your unit could be okay too. Should be able to get a pic tomorrow.

[Flying Dutchman]

Was able to localize what I belive is the feeding line. Black rubber hose through chassie connected to brown line that goes to the vem. Let the engine run for a while and pulled it apart. No hissing or blowing/sucking at all.. will pull the inner fender tomorrow and have a look.

[Flying Dutchman]

Finally found it! The vacuum hose was blocked by the front mount of the container for windshield wash (hope you can understand my poor English) Had the car in a workshop changing timing belt. They must hav put the hose on the wrong side of it and just tighten the bolt.. So no VEM error here.

[jamescarruthers]

Fantastic. Well done mate.