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8 & 10 cyl Bristol cars Type 407 onwards - restoration, repair, maintenance etc

Bristol 411 heater controls

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Old 03-02-10, 11:20 AM
Join Date: Jul 2008
Posts: 18
Default Bristol 411 heater controls

The mystery of Bristol heater controls .... These never seemed to work as I assumed the controls indicated.

In the course of restoring my 411, parts of the heating system were refurbished and the opportunity was taken to figure out what the controls actually did. The following is the note which I was given:

Direction Switch:

Off Foot area temp controlled
Demist Windscreen cold, foot area temp controlled
Defrost Windscreen temp controlled

Temp Switch:

Off Foot area closed, hot air closed
Cold to Hot Foot area open, temp in transition

From this I understand the main controls work like this: To demist the windscreen, select Defrost and Hot. To heat the footwell only, turn to Off and Hot. To heat the footwell and direct cold air to the windscreen, turn to Demist and Hot. To get cold air in footwell, turn to Defrost and Cold. To turn all off, turn both to Off. This seemed to be consistent with what I experienced in the past but I confess not to having tested it comprehensively since getting the note.

I would be interested to know what others have found.

Chris Browne
Auckland, New Zealand
Cellular: +64-21-617007
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Old 08-02-10, 10:46 PM
Join Date: May 2008
Location: Melbourne, Australia
Posts: 1,073


I can supply detailed pictures of the heater box if required but as for the original dashboard controls I can't help because I have an air con system fitted where the heater box used to be and the original original control knobs don't do anything (the A/C has it's own electrical control panel beneath the dash).

When I first bought my 411 and before the A/C was fitted, I did spend many hours getting the original heater box controls to work properly.

I discovered that the centre of control cable on the driver's side of the heater box had at some time become shortened and the outer sheath of the control cable was too long. Whoever cut or broke the cable didn't think to shorten the outer sheath as well ! This meant that the full travel of the lever connected to the cable was not possible. I managed to remedy this by shortening the outer sheath, but it involved dismantling the centre of the dash to remove the control cable. Unfortunately that was 10 years ago and I can't remember the details of what each control setting actually did.

I also have a question - when you use demist is it very powerful through the screen vents? and do you still get air through the eyeball vents at the same time?

My A/C unit (which I have finally got working) uses the original air ducts and vents. Demist has been replaced by "defrost", which moves a vacuum operated flap to direct air through the screen vents (it also opens a hot water valve and switches on the A/C). On Defrost I can detect air coming through the screen vents but a large proportion of the air still comes through the eyeball vents.

Regardless of whether Defrost/Demist is on or not, I have also noticed that the drivers side eyeball vents get more air than those on the passenger side. Is this the same as other 411s?

I know why this happens - if I look through the eyeball vents in the centre of dash with a torch, I can see a square aperture at the other end of the duct, which is much larger on the driver's side than it is on the passenger side. I was wondering if this was a conscious decision on Bristol's part to give preference to the driver over the passenger where fresh air and heating was concerned.

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