I have the ACC set to 20 deg and for 45 minutes, on a cold day, all is fine. After 45 mins, you can almost set your watch by it, the output from the ACC turns to cold. The only way to stay warm is to increase the temp setting to 'max'. Saab have suggested a new ACC unit but I am not convinced as it behaved correctly when tested. Is there a sensor somewhere that could be playing up? Any ideas gratefully recieved.
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I have a 2 year old 9-3 and the same thing happens on sunny cold days, on cloudy cold days all is fine. I've had all sorts changed under warranty but it always tests perfect. However on the centre of the dash board there is a black lump, if I cover this up on sunny days the heat comes back on. The handbook says that this sensor compensates for radiated heat from the sun, thats great but your feet freeze. I wonder if this is another Saab Quirk, or do I just have the unlucky car?.
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I think you'll find most climate controls use a photosensor to detect the amount of sunlight shining into the car (my car's got one, anyway). However I've never had the dramatic temp changes you guys are getting from cloudy to sunny days.
Possibly the sensor is playing up and the resistance of it is non-linear (or wrong, or bust, or something) so that the ACC unit thinks there's Equatorial sunshine overhead, and turns down the heat a bit...
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There's sensors all over the place, but the most likely is the internal temp sensor. They should be able to check the output resistance and check it against a given temperature. I don't know if the sensor is fed via a fan, as that may have stopped, or it may be bunged up with fluff and dust. If you can see where it gets its 'air' from, you may be able to get at it to clean/check. Assuming the Saab is getting on a bit, they didn't have full diagnostic function, so components have to be tested individually. The blend door has a motor drive, so that could be playing up as well. If it has got proper diagnostics, then they can read the values coming in from the various inputs. So whilst one of them may not have gone closed or open circuit and triggering a specific fault, they can check each value against a given. Does it reset itself if you turn the ignition off when it's going silly, then turn it back on again straight away?
Of course, it could be they are correct. Get them to swap it out on the understanding if they are wrong, then you get your old one back and a refund.
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Thanks for your thoughts Dave. I will have a go at my local Saab dealer (Haymill) to see what diagnostics they have got but my favourite non-franchised specialist plugged a test set into the system and gave it a clean bill of health. I will probably buy a new internal sensor and see what happens but its just not cold enough right now to give it a good test! I have had the sensor out and it was clean and the fan was running. I like your idea about 'borrowing' a new ACC unit.
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