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Heating / air con random behavior


Andyl
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I know these cars are supposed to be quite smart, but my P38's heater / aircon has a mind of it's own.

Some times blows hot, sometimes cold, you have to keep adjusting the temp setting to keep comfortable.

Local specialist tells me it reads faulty blend motors on the testbook, I have no reason to doubt them, they generally know what they're talking about, but I've never seen the fabled test book, could the output be misenterprated?

The faulty blend motors thing is a commonish fault, but from what I hear it is usually accompanied by a book symbol in the display, I never get that. Also the outside temperature reading is often way out and the behavior of the heater/aircon seems to relate to it.

In one journey (Saturday 14th April - pretty warm!) the car had been used then sat in the sun for an hour or so, started up and had a frost warning for over 5 minutes! Put the aircon on high as the inside was roasting, but it just blew warm air until the "outside" temp started to go up then the aircon began to cool down! Next time I started the car in the early evening the "outside" temp read 24 degrees!!

Does this sound like a blend motor problem? I have my doubts and they're not a cheap thing to change.

Comments welcome please!

Cheers,

Andy

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Sounds like its summat to do with the blend motors yes. However do be aware that they need "calibrating" with testbook. It may be that they dont need replacing they simply need re-calibration. As far as I know there is no way to do this other than with the relevant diagnostic kit.

Jon

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I have the book symbol now and then when I start my car.

When I do get it it seems that the ext. temp reading is way off.

The heater then seems to work according to this.

It may be worth just trying to replace the ext. temp sensor and

see what happens.

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Doubt its a blend issue,the ecu is more than happy to put up the book symbol if it does not get the correct feedback from them.What it cant tell though,is wether its loosing its own marbles - which is not uncommon,I've even had new ones that dont work.Best thing to do is to try a known good one in it.Ideally it should have a blend tune done on Testbook,in practice most of the garages that I work for seem to get away without doing it.

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Thanks folks.

My thoughts were ecu or sensors, but faced with the "test book says blend motors", I wasn't sure.

I'll pay them another visit for some deeper investigations, they may even have a good spare ecu we can try, but I certainly won't get the blend motors done at this point on the strength of the test book output!

Cheers,

Andy

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