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940 Heater Control Valve

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Old Oct 14th, 2019, 20:57   #41
J liddy
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Have the heating on this time of year it will soon dry out and no carpets or underlay till you find the leak!!!
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Old Feb 19th, 2020, 10:30   #42
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Sorry to bump an already bumped thread here.

Volvo 940 GLE estate - 2.3 non turbo, 1992, manual. Driven to the moon and back. My blower motor works - it pumps out air on all speeds around the dial. However, this is only cold air - twiddling the temperature control dial doesn't make the air any warmer. The dial itself is also very stiff - you can't really turn down from high past the half way setting to any lower level. No coolant leak or wet patches on the carpet etc.

Can I safely assume that the heater control valve needs replacing?

Is this the bit I need?

https://www.ebay.co.uk/itm/Car-Heate...QAAOSwDktbBduw

Also, the middle air vents above the centre console don't seem to pump out much air at all - any ideas here?
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Old Feb 19th, 2020, 10:34   #43
Laird Scooby
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Quote:
Originally Posted by McGandalf View Post
Sorry to bump an already bumped thread here.

Volvo 940 GLE estate - 2.3 non turbo, 1992, manual. Driven to the moon and back. My blower motor works - it pumps out air on all speeds around the dial. However, this is only cold air - twiddling the temperature control dial doesn't make the air any warmer. The dial itself is also very stiff - you can't really turn down from high past the half way setting to any lower level. No coolant leak or wet patches on the carpet etc.

Can I safely assume that the heater control valve needs replacing?

Is this the bit I need?

https://www.ebay.co.uk/itm/Car-Heate...QAAOSwDktbBduw

Also, the middle air vents above the centre console don't seem to pump out much air at all - any ideas here?
Have you got air-con?
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Old Feb 19th, 2020, 10:35   #44
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Have you got air-con?
No air con - I should have specified.

Out of interest, which Volvo 940s were fitted with air con, and which were not? Was it an optional extra from new on all trim levels?
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Old Feb 19th, 2020, 11:09   #45
Laird Scooby
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Quote:
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No air con - I should have specified.

Out of interest, which Volvo 940s were fitted with air con, and which were not? Was it an optional extra from new on all trim levels?
In that case, that's not the valve you need. The valve you need will be on the shelf between the Diplodocus Dimples and the Do-do doo-doo - in other words they are extinct!

There is another thread around and inside it is a link to how to convert a Mk1 Golf heater valve for use with the manual heaters on Volvo 7/9xx models, if i can find it later i'll post a link.

When the heater control is set ot "coldest", it turns the heater valve off. As it moves away from coldest, it opens the heater valve, regardless of how far from coldest. The control of temperature is done with the blend flap to mix cold (outside) air with warm (heated) air, there is no progression on the heater valve, it's either on or off.

If you are a good contortionist, have a torch and a small mirror, you should be able to see the heater valve above and to the left of the cutch pedal. You should also see the end of the Bowden cable that moves it. If you can get a glamorous (or even ugly) assistant to move the temperature from cold to hot and back while you observe the cable, you might get an idea what's going on.

As for the centre vents, assuming they are similar to the 740 (same heater box i believe so should be) they should have a knurled wheel at one end of each vent and turning that wheel should open the flaps behind. There should be some indication on the wheel to indicate it's opened the flaps :

<a href='https://postimg.cc/rdmr6cmf' target='_blank'><img src='https://i.postimg.cc/rdmr6cmf/IMG-20180802-184908310.jpg' border='0' alt='IMG-20180802-184908310'/></a>

You can see the white line on the wheel at the end of the vent indicating it's open. On manual heaters, these are fresh air vents only so will provide air from outside the car only. This can be boosted with the fan if wanted. Mine has air-con so i can set the temperature of the air coming out of the vents and turn them off with the front panel controls.

In short, first thing for you to do is investigate whether the cable is moving the heater valve.
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Old Feb 19th, 2020, 12:29   #46
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Quote:
Originally Posted by Laird Scooby View Post
When the heater control is set ot "coldest", it turns the heater valve off. As it moves away from coldest, it opens the heater valve, regardless of how far from coldest. The control of temperature is done with the blend flap to mix cold (outside) air with warm (heated) air, there is no progression on the heater valve, it's either on or off.
Dave, are you sure about that? I was pretty sure non-AC uses the NLA variable valve near the clutch pedal.

AC uses the flap mixer and vaccum controlled shut off valve.
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Old Feb 19th, 2020, 13:05   #47
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Dave, are you sure about that? I was pretty sure non-AC uses the NLA variable valve near the clutch pedal.

AC uses the flap mixer and vaccum controlled shut off valve.
The valve isn't variable Tony, the mechanism on the back of the heater control panel closes the heater valve when moved to the cold position, as soon as it moves from the cold positon, it opens the hear valve.

The manual heater still uses a blend flap.



Item #24 in that diagram is the blend flap.

Bear in mind, if the lowest temperature is 16C and you want 18C, if the ambient outside temperature is only 8C, you still need heating, that's why when the temperature selector is moved away from coldest, it opens the heater valve fully. If you look at the control mech on the back of the heater panel you will be able to confirm this. Yes, there will be a short transition area from closed to open but in the great scheme of things, this is very short and a few mm travel of the lever/knob on the front panel will be enough to completely change the state of the valve.

For this reason, a V3 lever arm microswitch or similar could be grafted onto the heater controls so it is activated on the coldest setting and wired to close a 12V solenoid valve when cold is selected. This means the solenoid valve will open with no power so when the cooling system is flushed, it flushes the heater matrix too.

I'm aware of the AC system using a solenoid valve block (that develops dry joints and causes problems) and the blend flap etc. I've had to repair the solenoid valve block on mine as i had little to no air flow from any outlet and when i did get flow, it was at the hottest possible. One of my first jobs on this 760 as i picked it up on one of the hottest days of the year 2016 so wasn't impresssed at frying myself with little or no airflow!
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Old Feb 19th, 2020, 16:31   #48
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Well I can tell you that my 95 940 non-AC, temperature control controls a variable valve via a control cable. To my knowledge there is no solenoid valve on my car.

I originally had a problem where the heat would not shut off completely. It turned out the hose clamp on the valve had been over tightened and distorted the valve so it didn't close. The variable valve is the cut off valve. Luckily this happened when the valve was still available. I am absolutely sure it is variable and cuts off the heating.

I can't be totally sure I don't have a flap control as well, but I don't see any need for one. I expected the flaps are for direction only (defrost, feet etc).

Over the years I had learnt that the cut-off valve is only for AC cars with the flap control.
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Old Feb 19th, 2020, 17:37   #49
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Quote:
Originally Posted by TonyS9 View Post
Well I can tell you that my 95 940 non-AC, temperature control controls a variable valve via a control cable. To my knowledge there is no solenoid valve on my car.

I originally had a problem where the heat would not shut off completely. It turned out the hose clamp on the valve had been over tightened and distorted the valve so it didn't close. The variable valve is the cut off valve. Luckily this happened when the valve was still available. I am absolutely sure it is variable and cuts off the heating.

I can't be totally sure I don't have a flap control as well, but I don't see any need for one. I expected the flaps are for direction only (defrost, feet etc).

Over the years I had learnt that the cut-off valve is only for AC cars with the flap control.
I didn't say you would have a 12v solenoid water cut-off valve Tony.

The heater control valve is NOT variable, it's either open or shut, as per the mechansim on the back of the heater controls. If someone can prove me wrong then i'll happily say they're right but even in old Minis, Moggy Minors and so on, the HCVs have been on or off, same with other cars that don't have a full-flow cooling system like my Jeep Cherokee XJ for example.

The diagram i added further up is for the manual LHD heater box, the RHD is mirror image and will have the temperature blend flap.
If you think logically about all i've said, you'll see it all makes sense.
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Old Feb 19th, 2020, 18:33   #50
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I have observed the cable moves in proportion to the heat setting and controls the valve in proportion to the cable movement. The Valve opens a slider cover which again is in proportion to the heat setting.

In the Haynes manual it says a mechanical cable is only fitted to non-AC cars. It does say a variable flap is used and shows the cable connected to the flap, however my car the temperature cable is connected to a typical heater control valve (similar to used in the 360), part #10.

Haynes also shows a vaccum controlled shut off valve is fitted to the non-AC, again my car doesn't have this. I'm pretty sure I researched all this when diagnosing my valve, after consulting the manual and finding significant differences.

Unfortunately my Vida is not working any more so I can't get the diagrams and check application years.

If I have time I'll have a further look at it. But I don't see how my control valve can be a shut off valve if its connected directly to the heater control and has a variable action.
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