Mk 7 - Heater (A/C) version - no heat, vacuum ok

[Jp71]

All,

When i twist the heater dial to hot the air stays cold. Its the AC version so i had a look at the heater water control valve just behind the firewall. When the engine is off, the little actuator arm is extended out and I can push it in and out. When the engine is running, the actuator is in in both hot and cold. I pulled off the vacuum hose feeding into this valve and sticking my thumb over the end of the hose when the engine was running i could feel a suction, to me suggesting that hose is fine. The suction was there in both hot and cold mode, turn the engine off and the actuator opens up again (presumably because the vacuum has gone).

This suggests to me the issue is with the control between the heat dial and the whatever that dial controls to turn the vacuum on and off, does that seem a correct assumption, and if so any pointers as to what the dial controls and what i might start to look at to fix it? thanks all

2008 mk 7, 350 TDCI,

[Airthies]

Blend door actuator,
motor failure.

Sent from my Pixel 8a using Tapatalk

[Jp71]

Blend door actuator,
motor failure.

Sent from my Pixel 8a using Tapatalk

The pipes going through the firewall are both cold, would this suggest its the blend door actuator as i would have assumed they'd be hot if that was the problem? thanks

[Airthies]

Is there any heat at the bulkhead vacuum valve?
That unit will divert between the cab heater or looping it straight back to the engine.
So regardless of the position of the valve or if the vacuum is working or not heat should be passing through that valve.

Sent from my Pixel 8a using Tapatalk

[Jp71]

Is there any heat at the bulkhead vacuum valve?
That unit will divert between the cab heater or looping it straight back to the engine.
So regardless of the position of the valve or if the vacuum is working or not heat should be passing through that valve.

Sent from my Pixel 8a using Tapatalk

Yeah, the plastic valve house with the actuator and the vacuum lines going into get warm, its just the pipes from that through the firewall that stay cold, cheers

[Airthies]

The switch in the cab doesn't directly control the vacuum like the non AC version.
Vacuum controls are electric and are in the front left inner wing area, below the engine fuse box and behind the headlight unit.



Sent from my Pixel 8a using Tapatalk

[Jp71]

The switch in the cab doesn't directly control the vacuum like the non AC version.
Vacuum controls are electric and are in the front left inner wing area, below the engine fuse box and behind the headlight unit.



Sent from my Pixel 8a using Tapatalk

Useful thanks, so you think i should start looking at fuses and/or the eclectic vacuum control? And if they seem OK then the electrics back to the heating dial?

When you say left (its a right hand drive) so you mean drivers side or passenger side? Its a RWD if that makes a difference? Cheers

[Airthies]

Is there any heat at the bulkhead vacuum valve?
That unit will divert between the cab heater or looping it straight back to the engine.
So regardless of the position of the valve or if the vacuum is working or not heat should be passing through that valve.

Sent from my Pixel 8a using Tapatalk

Yeah, the plastic valve house with the actuator and the vacuum lines going into get warm, its just the pipes from that through the firewall that stay cold, cheers

Those valves do fail, if it's not been changed already at that age I'd say it's doing well.

But usually the failure is external, with the housing cracking and leaking externally.

But if it's getting warm and it doesn't matter which position the vacuum valve is in I'd say the piston is jammed and the vacuum linkage has snapped.
I'd need to check mine tomorrow to remember which way it works.

Sent from my Pixel 8a using Tapatalk

[Jp71]

Is there any heat at the bulkhead vacuum valve?
That unit will divert between the cab heater or looping it straight back to the engine.
So regardless of the position of the valve or if the vacuum is working or not heat should be passing through that valve.

Sent from my Pixel 8a using Tapatalk

Yeah, the plastic valve house with the actuator and the vacuum lines going into get warm, its just the pipes from that through the firewall that stay cold, cheers

Those valves do fail, if it's not been changed already at that age I'd say it's doing well.

But usually the failure is external, with the housing cracking and leaking externally.

But if it's getting warm and it doesn't matter which position the vacuum valve is in I'd say the piston is jammed and the vacuum linkage has snapped.
I'd need to check mine tomorrow to remember which way it works.

Sent from my Pixel 8a using Tapatalk

Cool, that makes sense as the actuator/lever on the back moves out when the engine is cold but is always fully in when the engine is running

[Airthies]

The switch in the cab doesn't directly control the vacuum like the non AC version.
Vacuum controls are electric and are in the front left inner wing area, below the engine fuse box and behind the headlight unit.



Sent from my Pixel 8a using Tapatalk

Useful thanks, so you think i should start looking at fuses and/or the eclectic vacuum control? And if they seem OK then the electrics back to the heating dial?

When you say left (its a right hand drive) so you mean drivers side or passenger side? Its a RWD if that makes a difference? Cheers

Vehicle sides are always designated seen from the rear.

So as you say it's a Right Hand Drive
Then the left is passenger side.

I'd say you need to confirm the valve is opening and closing regardless of vacuum.
From what you've said, the vacuum cylinder is working as you can see it's control rod moving between on/off position?

Test this by disconnecting The hose when engine is running and a vacuum is present.
If it moves the the vacuum circuit would appear ok from an integrity point of view.

If valve is under vacuum when running, disconnect hose and plug it to hold vacuum to ensure brakes still work.

And see if heat flow is returned to the cab.
If it doesn't then valve is goosed.
If it does, then there's a reason the vacuum control valves are either being electrically opened or bypassing.

Sent from my Pixel 8a using Tapatalk

[Jp71]

The switch in the cab doesn't directly control the vacuum like the non AC version.
Vacuum controls are electric and are in the front left inner wing area, below the engine fuse box and behind the headlight unit.



Sent from my Pixel 8a using Tapatalk

Useful thanks, so you think i should start looking at fuses and/or the eclectic vacuum control? And if they seem OK then the electrics back to the heating dial?

When you say left (its a right hand drive) so you mean drivers side or passenger side? Its a RWD if that makes a difference? Cheers

Vehicle sides are always designated seen from the rear.

So as you say it's a Right Hand Drive
Then the left is passenger side.

I'd say you need to confirm the valve is opening and closing regardless of vacuum.
From what you've said, the vacuum cylinder is working as you can see it's control rod moving between on/off position?

Test this by disconnecting The hose when engine is running and a vacuum is present.
If it moves the the vacuum circuit would appear ok from an integrity point of view.

If valve is under vacuum when running, disconnect hose and plug it to hold vacuum to ensure brakes still work.

And see if heat flow is returned to the cab.
If it doesn't then valve is goosed.
If it does, then there's a reason the vacuum control valves are either being electrically opened or bypassing.

Sent from my Pixel 8a using Tapatalk

I think if I've understood the above correctly, and ive just been and done some testing

When the engine is running and the hose is attached the control rod is in - no heat - I can feel a suction from the vacuum hose however
When the engine is running and i disconnect the vacuum hose, the control arm pops out - still no heat

I think that means the valve is bung?

[andz327]

sounds about right, remove water hose and manually open valve from inside the pipe and put back on and try it for heat

Sent from my SM-G990B using Tapatalk

[Jp71]

sounds about right, remove water hose and manually open valve from inside the pipe and put back on and try it for heat

Sent from my SM-G990B using Tapatalk

thats a good idea thanks, presume you have to keep the vacuum hose off once open so that it doesnt alter the postion of the valve?

[Airthies]

sounds about right, remove water hose and manually open valve from inside the pipe and put back on and try it for heat

Sent from my SM-G990B using Tapatalk

thats a good idea thanks, presume you have to keep the vacuum hose off once open so that it doesnt alter the postion of the valve?

Yes, leave the vacuum hose off if it's forcing it closed.

If removing the unit to check it, make sure you've still got good glow through the heater matrix.
Depending on your coolant quality it's not unheard of for them to get blocked.

Stick the garden hose on it, make sure it's running clear and free

Sent from my Pixel 8a using Tapatalk

[Jp71]

sounds about right, remove water hose and manually open valve from inside the pipe and put back on and try it for heat

Sent from my SM-G990B using Tapatalk

thats a good idea thanks, presume you have to keep the vacuum hose off once open so that it doesnt alter the postion of the valve?

Yes, leave the vacuum hose off if it's forcing it closed.

If removing the unit to check it, make sure you've still got good glow through the heater matrix.
Depending on your coolant quality it's not unheard of for them to get blocked.

Stick the garden hose on it, make sure it's running clear and free

Sent from my Pixel 8a using Tapatalk

OK =,. so this afternoon I have

(i) taken off the valve, put it on the hose and when i manually move the actuator arm it changes the flow of liquid.
(ii) flushed the matrix
(iii) reinstalled the valve and left the vacuum off - this appears to get the pipe going through the bulkhead warm (it may have yesterday but i didnt pick it up) - no heat came through the vents however
(iv) when i turn the heat control dial the vacuum doesnt change and the actuator thingy stays in (in both hot and cold positions). When i pull the vacuum hose off the control actuator arm pops out.

SO based on that process of elimination i'm guessing the valve is ok.

It appears there is a fault
(a) with the control of vacuum
(b) with the transfer of heat across the matrix and out the vent

Are they both likely to be controlled by the little solenoid thing behind the passenger headlight under the water reservoir? I think that is the electrical control for the vacuum ??

Cheers