Heater vacuum valve

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Testie
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Heater vacuum valve

Post by Testie » Sat 05 Dec, 2009 1:16 pm

Heater tap was frozen so I purchase a new replacement from board sponser. The new plastic one,really only needed the tap, only has one hose attachment while the old one has two going to the vacuum element. So red pipe or green pipe? Both work either to open or close but it will be a bit annoying to get out and change the pipes over!
I do have the hose diagram but still at a loss to connect correctly. :?
Has anyone had experiance with these?
Col.

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Chai
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Re: Heater vacuum valve

Post by Chai » Sat 05 Dec, 2009 10:55 pm

The replacement tap has an internal spring that keeps the tap open. The tap shuts when vacuum is applied to the single connector.
My 1974 only had the single vacuum line that supplies vacuum when you do not want heat. That vacuum cable is coloured red.
Chai
1974 450SLC

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Re: Heater vacuum valve

Post by Testie » Sun 06 Dec, 2009 1:03 pm

Thanks

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Re: Heater vacuum valve

Post by Testie » Mon 07 Dec, 2009 4:47 pm

OK this is starting to S#$% me. :x The relay in the vaccum valve is on all the time (with ignition). Therefore there is a micro switch hidden in the dash somewhere. I have the control panel out but I can not see the switch/s. I am sure the heater valve was working except that the tap was seized before I tried to rearrange the plumbing.
Does anybody know where the switches are?
Help please I just want to enjoy the car not have it in pieces all the time. :cry:
Col.

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Chai
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Re: Heater vacuum valve

Post by Chai » Mon 07 Dec, 2009 11:10 pm

The microswitch is near the pivot end of the heater control slide lever.

My 1974 has a totally vacuum-based switch arrangement but I'm guessing that yours is similar to what is shown in the US-based service manuals, with electric micro switches controlling the vacuum units located on the firewall. I'm looking at the US schematic now and, based on the relative location of the red and green lines in the picture, I think the medium green line is the one that should supply vacuum to "turn-off" the heat.

However, you mention that the electrical wire to the vacuum relay is live/on all the time. This means that the micro switch thinks that one or both heater slides are in the 'not-DOWN' position. With the engine running, pull the electrical connectors off BOTH the red and green vacuum switches. Then check which red or green tube has vacuum and push that end to the heater tap. Plug up the other tube with a large screw into the end of the rubber tube.

You may be lucky and be able to gain access these micro switches by just removing the "above knee" panels under the dash. If not you'll have to remove the seats and then the entire centre console (encompasses the hand brake, gear lever, ventilation and radio).
Chai
1974 450SLC

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Re: Heater vacuum valve

Post by John Green » Wed 09 Dec, 2009 2:30 pm

Just read Chai's post, makes sense to me after our chat yesterday. How did it go?
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Testie
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Re: Heater vacuum valve

Post by Testie » Fri 11 Dec, 2009 8:41 am

I will pull the seat out and try to locate the microswitches on the weekend.Thanks and I will let you know how I go.
Col

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Re: Heater vacuum valve

Post by Testie » Fri 11 Dec, 2009 4:08 pm

:oops: Just about to pull my hair out when I discovered that PO had swopped the diagram on the levers around. That is the vent controls were on the outside and the heater tap on the inside levers. No wonder the microswitches did not work as I was operating the wrong levers. So back to the vaccum and with the power now off by operating the correct lever the single pipe from the vaccum control valve now turns the tap on and off. So simple!!Just need to remove/block the other one off and put the dashboard back together.
There are two lights behind the facia one big globe and one led size. Both are on grey wires and do not seem to have a holder to go to. There are other lights on the facia but these just hang there.The big one lights up the bottom panel of the radio when the panel is in place but where sholud they go. :?: Now I am on a roll I would like to fix them somewhere.
Col

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Re: Heater vacuum valve

Post by Chai » Fri 11 Dec, 2009 9:27 pm

Time to start a new topic.
Careful with large globes - their wattage may be too high = more heat = molten plastic dash panels or molten plastic globe holders.
Chai
1974 450SLC

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Re: Heater vacuum valve

Post by Chai » Fri 11 Dec, 2009 9:47 pm

Found my 16-year old photos - gotta get a negative scanner - showing the globes behind the ventilation/fan speed/air-con dash panel.

There are 2 globe holders located on the top left and right side of that panel, just below the radio slot. These light up the heat and ventilation sliders.
There is either one or two fibre optic leads that point toward these globes. The other end of the optic lead goes inside the rear-demist, sunroof (not for the SL: the rear passenger cabin light) switches.

I THINK there is one globe each for the fan speed and another for the air-conditioner control.

Hope this info helps.
Chai
1974 450SLC

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Testie
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Re: Heater vacuum valve

Post by Testie » Fri 11 Dec, 2009 11:12 pm

Thanks Chai, I will look in the daylight tomorrow. Thanks again.
Col

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Re: Heater vacuum valve

Post by Testie » Sat 12 Dec, 2009 1:16 pm

I can only find the globe on the heater fan, fits into a holder of sorts. There seems to be none on the Air con. switch but the big bulb behind lights that up.The one I am most conserned with is a small LED sized one with four brass tags around the bulb. Maybe they aresupposed to be glued somewhere on the front panel. The leads are grey and 8 to 10 inches long and are tied back to the other wires. Any more hints before I leave it behind the panel :?:
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Re: Heater vacuum valve

Post by AMG » Sat 12 Dec, 2009 1:48 pm

there should be 2 like the one in the bottom pic, they are for the slider illumination. they sit in the corners behind the indicator arrows at the top
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Re: Heater vacuum valve

Post by Testie » Sat 12 Dec, 2009 5:33 pm

Thanks JOEB, it looks like the holder part could be broken. More repairs tomorrow.
Col.

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Re: Heater vacuum valve

Post by Chai » Sun 13 Dec, 2009 12:02 am

Hi Col,

Here's the photo showing where the two top lights should be located.
Notice the burnt out plastic near the globes. The replacement light globes are 12V - 1.2W, are NOT LED-type and are therefore dimmable.
Buy a few spares as the instrument panel uses the same globes.
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Re: Heater vacuum valve

Post by Testie » Mon 14 Dec, 2009 8:43 pm

Thanks again the LED was only a reference to the physical size. The other holder is missing, as is the plug for the cigarette lighter/navman.
But at the moment all that is there is working and I will look for the other parts when time permits. :D :D
Col.

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Re: Heater vacuum valve

Post by TheMadRacoon » Sat 26 Jul, 2014 4:45 pm

Testie wrote:I will pull the seat out and try to locate the microswitches on the weekend.Thanks and I will let you know how I go.
Col
Picking up on an old thread....

My heater(s) work mostly fine. ie no heat when both heat levers are in the down (off) position - I can hear a 'click' when levers reach the bottom position; and there is heat when either lever is lifted. However I can't regulate the heat. I had a very quick look in the engine bay after working on something else and could see one actuator near the firewall on the passenger side. This has an actuating lever connected to what must be the heater tap on coolant line to the heater core. I didn't thoroughly test but when the driver's side lever is lifted up from the off position the actuator moves the tap lever fully, and retracts it fully when the interior lever is returned to the off position.

As mentioned I haven't checked to see if there is a second actuator or what happens with different settings of the two interior controls, but any leads as to what to check for? Would like to have max heat when levers are fully up rather than just above the off position, and ideally 50% heat when levers are half way up.

TIA
Emad,
TheMadRacoon
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