A/C Heater Niggles - Cryptic Fault Code

[greggers]

Hi, I've recently picked up a 2004 coupe with a few little niggles that need sorting... First on the list is the error with the A/C - I've run through the reset routine and I'm getting the error code AA82, which according to the table of errors is:

Type: DC
Description: Towards ground
Cause: Feedback
Identification: Mixing

So from that, something about the way it is feeding back some information is broken, I presume in relation to the temperature.

The actual symptoms of the issue are that it seems to stay on whatever temperature I start it up on... i.e. if I start it set to cold, I can't change away from cold once running/driving. Same if I start on hot, it'll stay hot and I can't make it cooler once running. It also seems to have an intermittent fault where I can't redirect the air, it does work sometimes but isn't consistent.

Does anyone have any pointers to where I should start?

As an aside, what's the best place to get a proper workshop manual that would include the diagnosis steps for this... I found one 4200 manual, but it didn't include this.

Cheers.

 

[Zep]

If I were to take a stab at it, I’d say the actuator for the hot / cold flap is not providing feedback on its position and the controller is deciding not to move the flap once running. That it only happens when the engine is on suggests some sort of ground issue. I’d be checking my earth straps.

 

[conaero]

If I were to take a stab at it, I’d say the actuator for the hot / cold flap is not providing feedback on its position and the controller is deciding not to move the flap once running. That it only happens when the engine is on suggests some sort of ground issue. I’d be checking my earth straps.

I would second that

 

[greggers]

Thanks @Zep & @conaero - I presume you're talking about the earthing straps in the engine bay... Will see if I can find them and give them a clean.

 

[hladun]

I've uploaded a 3200GT set of manuals to Dropbox. The 4200 is similar except for the engine and drivetrain. There's a lot of useful info here. It takes a little hunting but there's a good description of the A/C system along with wiring diagrams.

Maserati 3200GT Workshop Manual

Shared with Dropbox

www.dropbox.com