Interior ventilation - does this actually work?

Joss Walker · Nov 28, 2016

My car is normally a roof down only affair but I have taken it to work a few times over the last few weeks, part of my drive is really lovely and with the autumn colours and low sun etc its been a good start to the day, coming home has been mainly roof up and this is where I have begun to notice that the little slider controls for the ventilation that I assumed were meant to direct airflow either up or down don't really seem to do anything! Is this a case of 'they all do that' or should I actually be able to feel air blow out by my legs?

Thanks

Riverside · Nov 28, 2016

They are vacuum controlled, check for a leak.

zcacogp · Nov 29, 2016

Roof up / roof down? Must be a cab.

Unless they are different on the cab to that on the coupe then they are controlled by electric servos. These can get jammed or the connections can break. Have a read of Clarks Garage as that will explain things well.

http://www.clarks-garage.com/shop-manual/hvac-01.htm

Oli.

scam75 · Nov 29, 2016

Yes it works really well when working properly, which yours isn't unfortunately! As the boys have said it could be a vac leak. It could also be a servo motor or the control panel or any number of things. But my money would be on a vac leak.

Stuart

Joss Walker · Nov 29, 2016

Thanks all - at least it confirms there is something wrong with mine, and now the fun begins!!

zcacogp · Nov 30, 2016

I'm going to sound really fick by asking this but that's this vacuum-control system? I'm note sure I have ever heard of it.

Oli.

Riverside · Nov 30, 2016

I assume the OP's issue is with the recirculate flaps, they are vacuum controlled. If you have a vacuum leak they will stay closed, so your car mists up.

garyadams · Dec 11, 2016

Hi Joss

I also have a Cab and have been trying to sort out a heating issue just recently. Having spent much time upside down in both the drivers and passenger's footwell this is what or how I understand the system to work.

On the HVAC control panel
The top slider is the defrost slider and this operates the the uppermost electrical/mechanical servo in the passenger footwell to direct warm air to the window screen vents.
The bottom slider operates the bottom electrical/mechanical servo in the passenger footwell to direct air to your feet
The temperature control dial operates the middle electrical/mechanical servo in the passenger footwell to adjust the mixer flap for adjusting air temperature* out of the vents
The defrost button again operates the the uppermost electrical/mechanical servo in the passenger footwell to direct warm air to the window screen vents and turns on the fan to maximum
The recirculation button applies power to the upper vacuum servo in the drivers footwell in order to close the two external flaps adjacent to the fan air intake ports

*there is also the the heater control valve which is vacuum operated by the lower vacuum servo in the drivers footwell I believe this is also operated by the temperature dial

Gary

Joss Walker · Dec 14, 2016

Thanks Gary - really useful info, now I know it's only the one footwell in which I need to be upside down!!

I also need to fix the little clip to adjust the temperature (I have one in my box of things) so may try to tackle all in one go once some of my other more major issues have been addressed!

garyadams · Dec 15, 2016

Hi Joss,
Once you know the three mechanical servos are working and the clips are OK, a good check from the workshop manual is to put a vacuum on the tube going to the vacuum cylinder, have the temperature dial set to cold (blue) then turn the key to the first position and you should see the heater valve above the oil filter activate this proves the heater vacuum servo is OK. Then press the defrost button and the two flaps should close at the air intake, that proves the defrost vacuum servo as also OK.
The issue I had was intermittent, getting full heat which was uncontrollable, but the next time I started the car it worked fine. As I knew all the individual parts worked OK it only left the one way check valve (blue & white) at the back of the engine bay, which in my case is sticky, hence I wasn't always getting a vacuum.
I blew mine out with an airline (opposite way to the vacuum) which may have helped, as the heating worked OK the other day I used the car.
I may replace the check valve if I can find one at a sensible price!
Gary