Heating

[phil235]

I have a convertible 4.0, The heater set on auto blows hot all the time and the centre vent blows very little air. I have had the air con recharged
and this works fine on manual, the heater also works on this setting.
Any ideas ?

Regards Phil

[davidchevin]

Hi Phil

Have a look in the 'Aircon' forum (lower down the index). There's lots of good stuff there.

[phil235]

Thanks David.

Phil

[dogbitedavie]

i have a problem, whereby, if you start the car from cold, with the heater on hot, it will stay hot. but if the heater is hot and you turn it to cold and then back to hot, it just stays cold.... so i just leave it on hot, and wind the windows down !!

[almcl]

What year's your car?

If a Mk II Delanair is fitted (pre '87, I believe) can you hear the servo move when you change the temp setting?

If not, a new amplifier might be the answer.

[phil235]

Hi Al

Its a 94 and I don't think I can hear any thing.

Phil

[phil235]

Hi Al

Its a 94 and I don't think I can hear any thing.

Phil

[davidchevin]

Hi Al

Its a 94 and I don't think I can hear any thing.

Phil
Hi Al

Its a 94 and I don't think I can hear any thing.

Phil

Just because you've got a hearing problem, you don't have to repeat everything for our benefit

[almcl]

A '94 has the later heater, not the Mk II, so ignore the amplifier remark.

The Mk III system has a computer on the side and this can give problems. It also has a manual/auto option. Does yours give the same results in both manual (knob pulled out) and auto (knob pushed in) modes?

[Mark_B]

Hi

I think I'm the resident expert on Mk3, having wrote a website about it nearly 10 years ago now!

If after switching to Manual (left knob out), you can vary the heating effect between all shades of cold and hot, according to where the knob is pointing, then it is quite unlikely that there is any major problem.

If so, it's likely the problem is the temperature sensor(s) involved when the knob is set to Automatic. There's a sensor (cabin temp) just above the glove box, and another (intake air temp) located in one of the blower units. If one of them or wiring to it fails, the computer gets confused.

If it is that, a possible fault would be a detached connector plug.

Good luck!

[phil235]

Hi Al & Mark

Thanks for your replies.
Mine has a seperate button for Manual and Air con and it seems to be either too hot or too cold when set on manual but when set, the air con seems to be working Ok. The defrost setting also works Ok, what seems to be the problem is that the when set on auto it is over heating and the centre vents don't work.
Any ideas.

Phil

[Mark_B]

Yes of course, yours will be the later type, so no wonder what's been said about knobs and 'out/in' not make sense! Though I believe the principle is still the same between the 2.

Difficult to establish which symptoms belong to which mode. When the system set to manual, it works as designed (open-loop), is that right? That is, when in manual mode, can the air vent output temperature be set to all shades of temperature between cold and hot? Does the centre vent open during this exercise?

IMO seems one of these problems that without detailed symptoms it'll easily attract different opinions of varying believe-ability and risk acting on them. I saw it on another message board few days ago, the guy had spent 3 hours polishing his car one sunday then it kept stopping on the motorway. People on the list were writing messages saying it's the plugs, fuel filter, engine ecu, coil, etc...!
My money is on a cabin temp sensor, or some other sensor that's only ever involved when in auto mode.

[phil235]

Hi Mark

Thanks again for your reply. You can get varying temps from the temp nob but at any setting the centre vent does not open. Also it does not open with the air con working.

Phil

[poprivet]

I don't think mine has ever worked properly on auto, either too hot or cold. Maybe its just a hysteresis problem of the system over-compensating in an effort to achieve the set-point? So I leave it permanently on manual and turn the temp control up or down to suit my comfort at the time. Absolutely fine by me, I'm just glad its working at all!
Pop

[almcl]

Phil

if the centre vent never opens, the vac hose that supplies the actuator may be off, or leaking somewhere. It's a black coloured pvc tube coming from the back of the control unit. Should be visible with the cheek panel removed.