355 HVAC ECU

Here it is! In the luggage compartment, you have to remove the covering. I have not heard/read that this ECU is prone to fail. Have a look to all the fuses.
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We've actually sold about 5 of them in the last 12 months. Certainly not a 'high failure rate' item, but they do fail.

Part #46 on this diagram:
http://www.ricambiamerica.com/article_info.php?articles_id=1543

The item is here (excuse my photography skills):
http://www.ricambiamerica.com/product_info.php?products_id=241634

 

If replacing the ECU is the ultimate option, I would first open it to check for bad soldering. If no sucess, it is most probably the electronic output stage which drives the stepper motor. May be something reparable ... Sorry Daniel

 

Could it also be the circuit board that is integrated with the control knobs? I was having various issues with my HVAC system (only a couple fan speeds worked, temp not regulated correctly, etc.) and replacing the unit with a used pieced from another car did the trick.

 

Had to replace mine also this past year. A/C and heat worked intermittently, then less and less often. When it was in for the major I asked my mechanic to see if he could figure out what was the problem. He came back with the A/C ECU, said that when he looked in there was corrosion on/in it. Likely due to hose overuse (ie: pressure washing by a previous owner) causing water to get into that area where the ECU sits, and therefore corrosion. Anyway, the definitive diagnosis was made when he swapped out my ECU with one that worked, and all was well. Switching back, all was not well again. With that in mind, on his advice, I then proceeded to look for a used ECU because a new one was $$$ ("stupid money", as my mechanic put it, sorry Daniel). Well, I looked for many months to no avail (eurospares, italian recycling, etc). Eventually, it got cold enough, and I wanted heat enough to just pay the stupid money for it. Good news? The new one, as predicted, fixed the problem 100%, and was a 20 minute replacement job. Bad news? I think the ECU's go bad more than people think, given the difficult time I had finding a used one. Interestingly enough, the ECU didn't look that corroded to me. I even tried the Bosch contact liquid to solve the problem, with no success.

Oh, and after seeing the consequences of pressure washing, etc, I now do a lot of "speed shine" cleaning with Griott's stuff instead of regular car washes with water.

Good luck with your ECU investigation. Before you spend $$$ though, try to temporarily swap the ECU with one that you know works to confirm that's the problem.

 

That is indeed the A/C ECU in the front trunk, passenger side. Black plastic box, approx 1"X4"X4", mounted vertically beside the fuse (the famous "hidden fuse") and held down by a metal piece. The connectors are on the rear of the ECU (two of them), which is a bit of a PITA, but not impossible to disconnect. Once out, the ECU does indeed come apart pretty easily (this is self-explanatory, as you'll see once you have it out). On mine, the corrosion was NOT obvious, but by then my mech had already cleaned it up a bit. As an electronics guy, you may be looking at it under magnification, in which case you may see it.

Regardless of whether you see corrosion or not, I would find a friend with a 355 who will let you temporarily swap ECU's to see if replacing the ECU will fix your problem before spending $$$ on a new one.

Good luck with your troubleshooting.

John

 

That pump is needed to move coolant when the car is stopped and engine idleing. When moving there is enough engine speed for the water pump on the engine to move coolant through the heater core, but not when stopped. I had a 328GTS that would pump out cold air when stopped, but worked perfectly when moving. A friend with a 92 512TR did the same thing. The pump on the 355 must have been meant to correct this.