I have a definate noob question, i have a failing ECU on my 2002 legacy 3.0 . My air condition compressor is not getting any power from my ECU. Can i buy a used ECU and flash it to my car? Or do i have to get this done at the dealer. I have only worked on domestics my whole life, older models that are before all the diagnostic goodness...I have found several on ebay , that a reasonably priced. But i just need to know if it is a difficult task to swap it out and get it programmed? All answers are greatly appreciated !

The ECU usually grounds outputs to things like A/C when it wants to turn them on. Power usually comes from a fuse, through a relay coil, and then gets grounded at the ECU to complete the circuit.

So i should just look for a blown fuse? i hadnt had time to look at it.. I had my wife dropped it at the shop and they rendered the decision that the ecu was not sending signal to the compressor.. It has had fits in the past though, the A/C would stop working on long road trips. Then after a rest period it would return to normal ops ? now it doesn't work at all..

Edited February 28, 201214 yr by squirrely_1

there is a TSB, #10-74--2, date 09/01/02, for the 01-02 AC compressor.

 

i don't know if it is related to your trouble but i might be worth a search.

From what you say I wouldn't go right out and replace the ECU unless it is absolutely comfirmed that the signal coming from the ECU to turn on the AC fan isn't working when it should be. It sounds to me that there is a bad wire connection somewhere that is causing the trouble or a faulty fan relay. Proper trouble shooting will confirm the real problem.

 

If the trouble really is within the ECU you can purchase a rebuilt one for a reasonable cost and I don't think any programming is needed to make it work in your car. Sometimes programming is needed for extra options in some cars but I don't think Subaru has any of these, that I know of anyways. Removing the ECU from under the dash is fairly easy to do.

Edited February 29, 201214 yr by Cougar

You don't need to re-program anything to swap the ECU. But It's highly unlikely that's the problems. Subarus very rarely have ECU problems.

 

The AC systems has very many components, switches, etc that make it work. So a lot of stuff to break. Until all that stuff is tested, I wouldn't condemn the ECU.

You have a button in the cabin to turn it on, fuses, a few relays in the box under the hood, pressure switches in the system to lock it out if pressure is too high or low, temp sensors, etc. The clutch on the compressor could fail, and on and on.

Lots of components to fail, ECU is highly unlikely.

Thank you very much for all the info.. I will press on with the troubleshooting !

So found out that it is a multiple fail problem..revolution sensor fail, some receiver dryer fail, and a expansion valve fail..Not the ECU.. These all seem like things i can fix.. But where the hell are these parts located..lol.. Also who knows where i can find a munual that covers the H6 motor. Hayes, chilton.. none of these cover it..?

All the items you mentioned will be under the hood and are part of the AC system. Check Ebay for some copies of factory manuals. You can also purchase them from Subaru.