HEVAC Book symbol when AC turned off?

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jdennington

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For some reason I get the book symbol when I have the air con switched off but when I switch it on, it doesnt appear. A check has revealed that the air con compressor isnt kicking in, so why I dont get an error when it should be running is beyond me. I have even turned the interior fans off so there is no heating/cooling/ventilation going on but I still get the error pop up after a few minutes, probably less than 5. The system was overhauled around 6-8 months ago when the condensor was replaced. I can only assume that a sensor is failing, before I book it in for some diags, I thought I would ask on here to see if anyone had any pointers
 
That doesnt really make sense,which tends to point towards the HEVAC ecu failing itself.You may find weird codes logged,that dont add up when you view sensors in live data.
I keep a known good ecu on the shelf to help out in these situations.(I have even had faulty new ones in the past.)
 
Hi All

It is all too easy to condemn the HEVAC but actually it is doing exactly what it should do.

The HEVAC stores all errors that it logs but displays the book symbol only when there is a currently active error, this may well be one it has already logged. Therefore the book symbol will come up and disappear seemingly randomly, but this is what should be expected.

My advice would be get it plugged into the diagnostics and find out what it is reporting to be the error. You could get the refrigerant checked (is there any left in there?) but this will be about the same cost as a slot on the diagnostics and will only tell you if you are low on / out of refrigerant.

Whereabouts are you, if you are local to us we can plug you into our diagnostics and see what we find out. let me know if this is of interest.

Thanks
Andy
 
Hi Andy, thanks for your reply, I am based in the High Wycombe/Amersham area I agree with your comments and will need to get some diagnostics done first. If you are not too far away I would be more than happy to pay you for the diags check
 
Andy.R said:
Hi All

It is all too easy to condemn the HEVAC but actually it is doing exactly what it should do.

The HEVAC stores all errors that it logs but displays the book symbol only when there is a currently active error, this may well be one it has already logged. Therefore the book symbol will come up and disappear seemingly randomly, but this is what should be expected.

My advice would be get it plugged into the diagnostics and find out what it is reporting to be the error. You could get the refrigerant checked (is there any left in there?) but this will be about the same cost as a slot on the diagnostics and will only tell you if you are low on / out of refrigerant.

Whereabouts are you, if you are local to us we can plug you into our diagnostics and see what we find out. let me know if this is of interest.

Thanks
Andy
Click to expand...
I disagree - with the AC off button pressed the HEVAC ecu will not request a grant signal from the engine ecu and try to engage the compressor clutch.If there was a low gas pressure situation and the trinary switch failed to power the clutch a fault would get logged and the book symbol would appear.
If it was a blend motor issue the book symbol would be highly likely to come on a few seconds after boot up and stay on.Blower motor issues the same.
More likely is an intermittent fault with the heater matrix temp sensor or the evaporator temp sensor.But both of these should log a fault irrespective of AC on or off.
The only answer is to get it on Testbook and watch the live data.
 
The book symbol only appears when the AC is turned off, it takes around 2 minutes for it to appear. I can run the blend motors through the whole range from Hi to Lo with no problems and can distribute the air using the buttons on the front of the HEVAC unit correctly. If I have the AC switched on, no book symbol appears but the compressor does not engage, odd that this doesnt bring up a fault though as it makes more sense to me that way.
 
jdennington said:
The book symbol only appears when the AC is turned off, it takes around 2 minutes for it to appear. I can run the blend motors through the whole range from Hi to Lo with no problems and can distribute the air using the buttons on the front of the HEVAC unit correctly. If I have the AC switched on, no book symbol appears but the compressor does not engage, odd that this doesnt bring up a fault though as it makes more sense to me that way.
Click to expand...
Exactly - thats why it points towards the ecu failing,but till its gone on Testbook we are only guessing......
 
eightinavee said:
Exactly - thats why it points towards the ecu failing,but till its gone on Testbook we are only guessing......
Click to expand...

Hi eightinavee,

Completely agree with your comments, the point I was making was don't condemn the ecu until you have had some diagnostics on it, checked connections and all other cheaper routes first. You might replace the ECU and still not fix it, especially if it is a dodgy earth or similar.

It is all too easy, especially, it would seem, with a P38, to assume the worst and then be surprised when it isn't, hopefully before shelling out big time.

With regard to getting the diagnostics done, I am Bedfordshire based, work in Hertfordshire let me know if we can meet up somewhere and 'plug in'.

Thanks
Andy
 
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