ECU changed.. now no A/C

[cinquecento]

Hi all,

It was the first really hot day after dumping my 14CUX.. and was surprised that the A/C doesn't work. Plugged the old Lucas ECU back in.. and bingo!!.. A/C worked.

What happens is the A/C clutch doesn't engage...and the ECU wires that are A/C related seems to be :

21 Yellow/Black Air conditioning thermostat input, if fitted

33 Black/Grey Air conditioning compressor clutch relay, if fitted

36 Black/Green Air conditioning condenser fan output, if fitted


Am I correct in assuming that wire 33 provides the ground for the clutch relay after the A/C console switch engaged.?

Is there anything esle I need to consider?.. thanks

[OscarT]

Listen here Bruce

Don't be coming on here complaining about your A/C not working in really hot weather - we're freezing our nuts off over here!

Go jump in a Bingabong or whatever.

OscarT

[dnb]

You need to use one of the aux outputs of the ECU to operate the compressor switch.

If I had AC in mine I would set the aux output to switch the compressor off at full throttle, but on at other times. I believe it is a ground switch.

No idea what the other 2 signals are doing, but I suspect the thermostat input is a safety cutout.

[Uncle Fester]

I'm guessing here, but when it was mapped was the a/c allowed for?

If the default setting for each site is 'a/c off' then you're going to have to set it to 'a/c on' in the required sites.

Which ECU have you fitted?

My Emerald will be fitted shortly and I have a/c too. If you find the answer let me know. It might save me some trouble.

[shpub]

The two other signals are quite importanT;

The thermostat controls at what temperature the A/C compressor is switched off to prevent icing. The ice melts and dumps itself into the interior or other places where the water shouldn't go.

The fan is to ensure that the A/C rad has air flowing through it.

The ECU also does some other stuff like turning the compressor off when the engine revs rich a certain point to prevent the compressor from being over revved and seizing. It also disables the A/C if the water temp gets too high as running the aircon does increase the engine running temp.

It does quite a bit to provide a fairly intelligent control.

PS

The ECU also adjusts the mapping to cope with the additional load including raising the idle temp so that the AC doesn't stall the engine.

Edited by shpub on Monday 10th December 12:28

[The AJP Griff]

I had this issue when fitting the Omex to my car.You dont need a switch from the ecu,you just need to provide an earth to the a/c compressor relay,from memory this is a switched earth as long as the Lucas is switched on basically,so theres no other link between the Lucas system and the a/c system.Just give this relay a permanent earth.It's pretty simple to do,so i'll have a look through my notes for you Lindsay,and i'll mail you something.You can of course use an a/c high idle from your ecu if it provides this facility,but in practice i found this was not really worth the bother,as the engine speed drops very little when the a/c kicks in,and my car already idles at 900-950rpm with the cam i run.

Edited by The AJP Griff on Monday 10th December 13:28

[dnb]

Any modern ECU worth its salt should detect the additional load and control the idle valve/spark timing appropriately. Therefore there should be no need to worry too much about stalling at idle. (Steve - I think you mean idle speed, not temp )

Configuring an output to be off at high RPM or high throttle position, but on at other times should be easy too. So this deals with all of the compressor stuff.

I'm surprised the engine ECU does anything at all with the thermostatic shutoff - surely in a sane system this should be a stand alone safety feature?

[shpub]

The AJP Griff said:

I had this issue when fitting the Omex to my car.You dont need a switch from the ecu,you just need to provide an earth to the a/c compressor relay,from memory this is a switched earth as long as the Lucas is switched on basically,so theres no other link between the Lucas system and the a/c system.Just give this relay a permanent earth.It's pretty simple to do,so i'll have a look through my notes for you Lindsay,and i'll mail you something.You can of course use an a/c high idle from your ecu if it provides this facility,but in practice i found this was not really worth the bother,as the engine speed drops very little when the a/c kicks in,and my car already idles at 900-950rpm with the cam i run.

Edited by The AJP Griff on Monday 10th December 13:28

Be careful. One of the reasons I think why my AJP went to meet its maker was the fact that someone had done exactly that. The compressor ended up running virtually all of the time including at highish revs which overuns the compressor. Compressor eventually siezed and this loaded the crank bearings which then threw a major wobbler.

Edited by shpub on Monday 10th December 16:49

[The AJP Griff]

shpub said:

The AJP Griff said:

I had this issue when fitting the Omex to my car.You dont need a switch from the ecu,you just need to provide an earth to the a/c compressor relay,from memory this is a switched earth as long as the Lucas is switched on basically,so theres no other link between the Lucas system and the a/c system.Just give this relay a permanent earth.It's pretty simple to do,so i'll have a look through my notes for you Lindsay,and i'll mail you something.You can of course use an a/c high idle from your ecu if it provides this facility,but in practice i found this was not really worth the bother,as the engine speed drops very little when the a/c kicks in,and my car already idles at 900-950rpm with the cam i run.

Edited by The AJP Griff on Monday 10th December 13:28

Be careful. One of the reasons I think why my AJP went to meet its maker was the fact that someone had done exactly that. The compressor ended up running virtually all of the time including at highish revs which overuns the compressor. Compressor eventually siezed and this loaded the crank bearings which then threw a major wobbler.

Edited by shpub on Monday 10th December 16:49

it's not on the AJP Steve,it's on the RV8 Griff.I was told the compressor and std pulley will cope with 6k rpm no problem by my trusty a/c man,and two years later that certainly seems to have bared out.No problems at all.

[trackcar]

shpub said:

The AJP Griff said:

I had this issue when fitting the Omex to my car.You dont need a switch from the ecu,you just need to provide an earth to the a/c compressor relay,from memory this is a switched earth as long as the Lucas is switched on basically,so theres no other link between the Lucas system and the a/c system.Just give this relay a permanent earth.It's pretty simple to do,so i'll have a look through my notes for you Lindsay,and i'll mail you something.You can of course use an a/c high idle from your ecu if it provides this facility,but in practice i found this was not really worth the bother,as the engine speed drops very little when the a/c kicks in,and my car already idles at 900-950rpm with the cam i run.

Edited by The AJP Griff on Monday 10th December 13:28

Be careful. One of the reasons I think why my AJP went to meet its maker was the fact that someone had done exactly that. The compressor ended up running virtually all of the time including at highish revs which overuns the compressor. Compressor eventually siezed and this loaded the crank bearings which then threw a major wobbler.

Edited by shpub on Monday 10th December 16:49

The MBE doesnt cut the AJP8 compressor anyway .. the aircon is wired into the MBE but if you look at the function control it's not disabled even at full throttle/max revs. Your seizure would have heppened as std whether your wiring had been modded or not.

[The AJP Griff]

How did you get on,Lindsay?

[cinquecento]

Yep.. finally got around to digging out my wiring loom.

Grounding pin 33 works.. so now I have an air conditioner just in time for winter!!!..however I will take note of the suggestions on when/where to run the A/C in terms of high rpm/icing.

Thanks all