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[nordic]

Hello,

Does removing the HBV vacuum pipe, and blocking it, prevent cold air to the cabin?

I know doing this should provide constant hot water through the heater matrix, but would this prevent you getting cold air into the cabin even if you selected 'cold' on the dials?

Cheers,

Andy

[ffcgary1]

Seem to remember that the controls fail to respond to settings on the dial if vac pipe disconnected. the HBV operates on a vacum principle to open the valve.

[alank46]

No, the HBV operates on a vacuum to CLOSE the valve and stop water flow to the heater matrix.
If the vacuum pipe is removed from the HBV and plugged it will have no effect on the operation of the other vacuum controls.

Seem to remember that the controls fail to respond to settings on the dial if vac pipe disconnected. the HBV operates on a vacum principle to open the valve.

[nordic]

So - if hot water is always flowing to the heater matrix - would this have any impact upon cold air entering the cabin when I select 'cold' on the dial?

Cheers,

Andy

[Andy H]

If the vacuum pipe to the HBV is plugged then there should still be vacuum available to operate the flaps in the climate control.

With hot water flowing through the heater matrix there will be hot pipes in the cabin and some heat transfer within the climate control but I would expect 'cold' to mean cold. The control might be poor though because instead of mixing cold air with outside air the system will be mixing cold air with hot air (possibly very hot if it is already hot outside)

[amba]

I have always had difficulty getting my head around how this HBV actually works too 

If you have climate set on cold does this close the valve off in the HBV and stop all coolant flowing through the heater matrix ?

When you increase temp above LO does valve open in HBV and allow the coolant to flow around the entire system ??

[Andy H]

I have always had difficulty getting my head around how this HBV actually works too 

If you have climate set on cold does this close the valve off in the HBV and stop all coolant flowing through the heater matrix ?

When you increase temp above LO does valve open in HBV and allow the coolant to flow around the entire system ??

The climate control panel knows the outside temperature so I expect that the control should be more sophisticated. (wouldn't count on it though )

[amba]

More curious about why the HBV seems to be the "achillies heal" in the system really.

It seems to be the diaphram valve inside it that leaks but if it is only being controlled by a vacuum to open or close it why is it such a problem bit of kit ?

Does coolant always flow through it but just get shut off from going through the heater matrix when digital controls set to LO

[2woody]

The Omega heater is of the "air-blend" type. This means that the heater matrix is provided with a full flow of hot water at all times, irrespective of what temperature you've selected. The air into the cabin is either run through the matrix if you've selected "hot", or bypasses the matrix if you've selected "cold", or any combination between the two.

Now for the exception. On a car fitted with air conditioning, there is an extra valve, the HBV, which can be operated to stop the hot coolant reaching the heater matrix, but this ONLY operates when the aircon is "on" and BOTH temperatures are selected as "LO". It diverts all of the coolant, there is nothing other than open or closed for the valve.

If you move just one of the temperature selectors away from "LO", then the HBV opens to flood the matrix with hot coolant. This does not mean that the cabin heats up, as 99% of the heater air is still going through the heater without going through the matrix.

If the HBV vacuum is disconnected, cabin hot will still be hot and cabin cold will still be cold, just not quite as cold as with a fully-functional HBV.

[nordic]

Fantastic Answer! Cheers!

I am going to check the suction of the vacuum pipe that leads to the HBV at different temps tomorrow.

Following that excellent answer, I feel to do so is no longer required, but I will have a go just to see and will report back. I expect it will only suck when the dial is on 'low'.

Again, thanks for the answer

Andy

[nordic]

I have now tested the vacuum pipe suction at different cabin control temperatures.

There is suction beyond just the 'Lo' setting. The suction appears to be triggered by the cabin temperature. Coming on when the temperature you set triggers the cabin fan to start. Go up in temperature and the fan stops - as does the suction.

This suction is present if the air-con is on or 'econ' is selected.

So if this vacuum pipe is blocked will it impact upon cold air coming into the cabin?

Will the air remain hot regardless of what cabin temperature I select?

[Andy H]

I have now tested the vacuum pipe suction at different cabin control temperatures.

There is suction beyond just the 'Lo' setting. The suction appears to be triggered by the cabin temperature. Coming on when the temperature you set triggers the cabin fan to start. Go up in temperature and the fan stops - as does the suction.

This suction is present if the air-con is on or 'econ' is selected.

So if this vacuum pipe is blocked will it impact upon cold air coming into the cabin?

Will the air remain hot regardless of what cabin temperature I select?

No - the climate control will still blend the two air streams to try and keep you comfortable. The only difference is that when you don't want heat the poorly insulated ends of the heater matrix will still be warming your feet in the footwells.

The other important point is that the HBV is a bypass valve not an on/off valve. Even when flow is stopped through the heater matrix there is still flow through the back of the cylinder heads . If you block it completely there is less coolant flow for cylinders 5 & 6

[2woody]

I have now tested the vacuum pipe suction at different cabin control temperatures.

There is suction beyond just the 'Lo' setting. The suction appears to be triggered by the cabin temperature. Coming on when the temperature you set triggers the cabin fan to start. Go up in temperature and the fan stops - as does the suction.

This suction is present if the air-con is on or 'econ' is selected.

So if this vacuum pipe is blocked will it impact upon cold air coming into the cabin?

Will the air remain hot regardless of what cabin temperature I select?

something's wrong there - are you sure that you've got the correct vac pipe connected to the HBV ?

I'm only just up the Tyne valley - want me to have a look at it ?

what year car is it ?

[Andy H]

I have now tested the vacuum pipe suction at different cabin control temperatures.

There is suction beyond just the 'Lo' setting. The suction appears to be triggered by the cabin temperature. Coming on when the temperature you set triggers the cabin fan to start. Go up in temperature and the fan stops - as does the suction.

This suction is present if the air-con is on or 'econ' is selected.

So if this vacuum pipe is blocked will it impact upon cold air coming into the cabin?

Will the air remain hot regardless of what cabin temperature I select?

something's wrong there - are you sure that you've got the correct vac pipe connected to the HBV ?

I'm only just up the Tyne valley - want me to have a look at it ?

what year car is it ?

Sounds correct to me.

No vacuum = flow to heater matrix.

When the climate control doesn't want heat it applies vacuum to stop the flow.

[nordic]

Yes - definitely the correct vacuum pipe.