Aircon Not Working Because Of Ecu?

[jwah]

I recently just took my car to an auto elecy and he said there is nothing wrong with my air con, but there could be somthing wrong with my computer? Ive thought of putting my pfc in to see if that'll make it work. Anyone had this problem or know how to fix it? I have a 32 GTR

Cheers

[BH_SLO32]

Reviewing the wiring diagrams and ECU input/output signals, there are 2 wires on the ECU that interact with the A/C namely pin 46 (A/C switch signal) and pin 9 (A/C cut signal).

It appears that when the A/C button is pressed the ECU detects this via pin 46 and responds by earthing the A/C relay signal wire (pin 9) which controls (in part) the operation of the A/C compressor.

I say "in part" because the A/C relay signal wire first passes through a dual pressure switch before arriving at pin 9 on the ECU (ie dual pressure switch is in series with pin 9). This inevitably is to ensure that the A/C system has adequate gas pressure before allowing the compressor to switch on.

I think the pressure switch is located on the A/C filter canister which resides in front of the radiator on the drivers side. Provided the system is gassed the compressor should switch on when pin 9 earths the A/C relay signal wire.

Assuming the PFC controls the A/C in the same manner as the factory computer (I would be surprised if it didn't) then plugging the PFC in may help to eliminate the ECU as a possible cause of the problem.

Failing this you can check the voltages at pin 46 and pin 9 before and after the A/C button is pressed and check what the ECU is doing.

I hope this helps.

Cheers

[jwah]

Thanks for the Detailed reply. I will have to plug in the pfc and see what happens, just got to get around to it. The auto elecy was pretty certain it had somthing to do with the computer in it because he actually got it working by bridging it out or somthing at the computer. So with what your saying, sounds like it could be the computer. But i'll have to find out. Thanks again

Cheers

[RB30-POWER]

You need to first check that the computer is receiving the aircon request signal from the switch/climate control.

If the ecu input is seeing the request signal, but not operating you then need to check that the other side of the circuit is fine. To do this just switch the output side at the ecu and confirm that it all starts working. (This will rule out things like high/low pressure swicthes)

If that makes it work, then the ecu is the culprit.

Rather then replace the ecu, I would just wire up an extra relay to bypass the computer.

I would still provide the ecu with the switched aircon request signal though, so that it changes the idle strategy for AC mode.

This is basically the same as what was said above, but i wanted to point out that you really only need to test the two sides of the ecu to quickly narrow where the problem lies, you can then narrow it from there.

Im sure your auto elec knows what he is on about.

[jwah]

Ok that makes heaps of sense. But i was just thinking of putting my PFC in to see if it works, and if the air con works, i wont bother getting anything fixed until i go and get my car tuned. Ive had it sitting around for about 3 months now, just finishing off my engine still. But i thought i'd fix a few bugs first. Ive never actually pulled out the computer before, but im guessing it'd be alot easier just switching it then checking all those things youve just said?

Cheers

[RB30-POWER]

Great idea

Connect the PowerFC up and if the AC switches on, it will prove that the relay/switch inside the standard ecu is fried.

Too easy....

[noone]

Draggin up an old post I know but am wondering if the dual pressure switch would prevent the aircon from switching on after having the gas updated to r134 (i think that is what it is) I have been told that r134 is a higher head pressure than the older r12 that the system was designed to run. Does the switch only work if the pressure is to low or will it switch/not switch if pressure is to high as well. Going to have a chat with the local aircon guy tomorrow so will post back any findings Just thought someone on here may be able to confirm my suspicions

[PM-R33]

Bumping an old thread.

Can the low pressure switch itself fail? I have had the gas checked and there is plenty in there, everything seems to be operating the way it should be but the clutch on the compressor wont engage.

If I earth the low pressure switch it will engage the compressor and work properly so is it possible that the switch itself is f**ked and thinks there is low gas when there actually isn't?

Edited November 4, 2010 by PM-R33

[noone]

Checking the low pressure switch with a multimeter will answer your question

Should see a circuit, alternatively earth the other side of the switch, car side, that will prove it as well.

Next step back is pin 9 I think on the ecu, hopefully you dont have the problem I do with the ecu not earthing that output

[PM-R33]

I ended up sorting it out

Turned out to be a bad connection from the ECU to the Aircon output wire. Even though the ECU said it was switching, in reality it wasn't.

I traced the wire back and found where the connection had broken.

Once I changed the settings on the Vipec to make sure it was swtiching the correct way it kicked in and started working.