Factory ECU - A/C pins do what?

[1JZ-Rolla]

So on our OEM ECU's, there are some or all of the following pins:

A/C
A/C 2
A/C Mag clutch


But where does each wire come from/go to, and what purpose does it serve? It seems most 80's onwards toyotas have the air conditioning controlled by its own module/amplifier and switch unit (dash), but what is the relationship with the ECU, other than simply to increase idle speed when the aircon is on?

I'm struggling with my setup at the moment after an engine conversion, A/C compressor won't stay on, and idle up function works in reverse to what is expected?


any advice and info appreciated

Cheers
Phil

[Ken_T]

I can't help you in relation to toyotas specifically but I went looked into this good when I was wiring a megasquirt for SR20. In this application, the pin from the ECU went to switch on the hvac panel. The switch was NO and would connect to earth (or power) when activated. This told the ECU to switch engage the compressor on if all other conditions were satisfied. To do this, the ECU would ground the A/C mag clutch pin allowing the compressor to engage and idle to increase.

One of the wires also went to a NC switch in the evaporator to tell it to stop operation of the A/C when the evaporator was frozen over(switch opens).

I might have the open/closed and powered/grounded side mixed up but I hope you get the idea.

[DX20VT]

Cant comment on your one specifically,

but a lot of cars run the AC through the engine ecu because....

1. It will not let the AC clutch engage below a certain RPM to help prevent the engine stalling

2. When the ECU recieves the AC signal, it will raise the Idle speed before it allows the clutch to click in, say 0.5 sec or so,
so that the revs will not drop then pickup.

3. it will disengage the AC when the car starts to get above a certain temperature to help prevent overheating

[dumbass]

a/c or ac1 tells ecu that u have switched air on and idles motor up
acmg triggers a/c clutch relay

ac2 or act or sometiems theres other named pins for ac normally goes to ac amplifier for something
u normally need to bypass it
or if its an mr2 it gets trickier

we dont know what car or motor it is
anyway its not all the same for all toyotas

[CrUZida]

A lot of cars will also disconnect the AC at full throttle with the AC MG pin.

[1JZ-Rolla]

Ok cool, those approaches seem logical, so I could assume that there should be continuity between the A/C Mag Clutch pin and the single wire at the compressor for the lockup clutch, as a first functional check?

Not sure still of the difference between A/C 1 and A/C 2 pins though.......


THanks

[DX20VT]

so I could assume that there should be continuity between the A/C Mag Clutch pin and the single wire at the compressor for the lockup clutch, as a first functional check?

Nope, doubt it.

the ECU cannot supply enough current for the clutch.
the ECU will trigger an AC relay somewhere,
and there is may be a pressure switch in the circuit between the ECU and the relay too.

YOu will really need to find a diagram to tell what goes where, unless someone knows it from memory.

What car is it again?

[dumbass]

what fking car is it and what motor hehehehe
they all work different
sometimes u cant just wire this to that
u need to trick things

[1JZ-Rolla]

Good point. Have been through the vehicle (JZA70 Supra) switch and relay diagrams and can't find the A/C Clutch relay listed anywhere.. though there has to be one hey.

Engine is from a JZX100 Chaser. Major headfark at times on the wiring side.


There is a 3 way pressure switch in the engine bay, I understand the controls side of things needs to see the gas line pressure as being above a minimum, but below a maximum point before it will pull the compressor clutch, not sure though what the mid-point is supposed to trigger. Secondary radiator/condenser fan perhaps.

I'm digging through wiring diagrams as we speak, and its doing my head in

[1JZ-Rolla]

Thanks Dumbass

JZA70 Supra
Single turbo VVTi 1JZGTE from JZX100 Chaser

[dumbass]

ok cool
well the acmg mut be working ince it turns on for a sec
they both have the same pinouts
so its either a pressure switch problem
have u got gas in the system
they can get fiddly at times trying to solve but most of the time is in ac amplifier not the engine ecu

[dumbass]

oh ok its a vvti
well they get bit more complicated
easiest way to fix is
put a relay between a/c wire and the acmg and dont run thru ecu
so ac works when ac amplifier turns it on
to get it to work properly using the vvti ecu u sometimes need to wire up the vvti amplifier
i have had in the past when doing 3s swaps in mr2s the ac2 or act pin sometimes might be 5 volts or somthing
so i ran it off the tps power but i would not do this for the 1j until u find what it does
maybe check the voltage on the ac2 wire when its not connected
if its 0v then trigger to 12v ign but thru a 1 k resistor so its nto a dead short
if its 12v then trigger the ac2 to 0vs thru the 1k resistor
if that doesnt work then maybe try 5v trigger

[1JZ-Rolla]

Yep its gassed, just a couple of days ago, that's when we identified the issue (was completely vacced down for the engine conversion, so couldn't test the A/C operation until re-gassed). System has sufficient pressure checked from the manifold gauge set so the pressure switch should be happy (assuming no fault there, it was fine before).

The other bit that is confusing me is that with the aircon switch off, the engine idles as 1100rpm. Yet with it on, idle drops to 800rpm, reverse of what you'd expect right?

[dumbass]

well i might have found yr problem

ac wire i think might be a ground not a 12v
that might be y its idling up as when air is of it thinks its ok
so cut the ac wire and measure voltage on free wire to ecu
and if its 12v then ground it thru 1k resistor
and opposite if its 0v

my info is in jap so fkt if i know what they mean
but ac comes from amplifier terminal mgc

ac2 comes from amplifier terminal efi0

then there is another wire thwo which comes from ac amplifier terminal efi1

everythign is in jap so hard to navigate so i think im on the right 1j

[1JZ-Rolla]

Thanks mate, much appreciated, sends me in the right direction at least.

Any idea what the AC2 is actually supposed to do on the VVTi? I can't see anything to do with that on the old twin turbo ECU.
I assume THWO is to shut-off the compressor if the evaporator is too cold on the VVTi setup?



I think i'll do a functional test of the actual compressor clutch tomorrow, running 12V to the clutch pin at the compressor, to make sure it can actually physically lock up.

Then i'll follow your instructions above to see if I can make sense of the idle-up issue, and hopefully it will make sense then.


THanks again for looking into this, its a bit over my head!