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Discussion Starter #1
Been having some weird stuff going on with my ACC. All my blend motors where replaced (new ones) and all is good for 4 months, then occasionally I get the book symbol upon starting the car and it blows heat regardless what setting. I was thinking temp control blend motor. But the error code only happens randomly, and 99% of the time if I shut the car off and re-start it goes away.

Now I've noticed my exterior temp always seems to start at 36 degrees (the temp it was several weeks ago) with frost symbol and takes about 4-5 minutes to display right temp.

As I hear exterior temp sensors rarely fail i was thinking of swapping a used ACC to see if that is part of the issue. In the past on my other P38's if a blend motor failed it failed and the error code was always present. That is the one stumping me. Sadly I don't have access to pull codes.
 

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Could be the recirc motor, as depending on the outside temperature, the recirc is generally open but only closes with very high and very low temperatures. For me, this means I get a book symbol on 28 degree (celsius) days but not otherwise.
 

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@Rover-ABQ, I have a Nanocom if you want me to pull the codes from the HEVAC unit to see what the book symbol is popping up for. Let me know.
 

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Im having a similar problem , only on hot days thou . the air con is low on gas having it recharged next week will see if this fixes the problem. I think its going out off range trying to compensate for the air con. how is the air con in yours?
 

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Discussion Starter #8
Im having a similar problem , only on hot days thou . the air con is low on gas having it recharged next week will see if this fixes the problem. I think its going out off range trying to compensate for the air con. how is the air con in yours?
AC seems ok. I have noticed when I set a temp the fans seem to go on too long going past the set temp. I assume the interior temp sensor maybe faulty as well.
 

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Exterior temperature sensor problem starting at 0 deg celcius is a problem of poor connection at sensor plug(or voltage drop during starting).
Clean sensor plug pins or replace plug.
 

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Best to check stored faults with Nanocom. At same time check all the temperature inputs, which can help spot any bad connections. If any of the sensor values are way out, the HEVAC can do strange things.

E.G, I have occasional intermittent connection on the heater pipe sensor, so the system thinks the water is colder than it is, and makes the HEVAC move the temp control flaps a bit on the warm side !! When the sensor is working correct, the cabin temp regulates nicely. (gotta fix that connector before the summer)
 
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