VP Aircon ECU controls :Att donauto.

[jas24zzk]

I was going to thro this into Other projects, but figured others could benefit from the curve balls that can come with mods/upgrades.

Problem. No power to Aircon compressor.

Vehicle. 1983 Toyota Hilux Extra Cab, with a series 2 VP commodore V6 conversion, with ECU controlling all functions including Fans and A/C.


The hilux sends pwr to the pressure switch, then out to the compressor.
This is part 1 where i may have it wrong.

Does the VP send pwr or gnd to the ECU?
Does the ECU then send GND to a relay? (it does for the fans)

I could cheat and bypass the ECU, but that would complicate fan control...i'd have to stick in a relay, and diodes to bring an engine fan in and not upset the ECU. this also defeats the purpose of having the ECU control it.

Thoughts...

cheers
Jas

[boofhead]

It is not always the case though it is considered normal that an ECU will ground a circuit to make it work rather than prvide the power for the circuit. Obviously to limit current this grounded circuit drives a relay rather than the device directly.

[jas24zzk]

Thats my thought also. Tho need to confirm if the input is pos or neg.

[hybrid]

If you have the original harness, can you not trace it?

[donoauto]

On a VP, when you select any fan speed, power is supplied to the A/C switch from fan switch. When the A/C switch is turned on, that power then travels through the thermostat & pressure switch. The pressure switch output then supplies power to 85 or 86,as well as terminal 30 of the A/C clutch relay as well as supplying power to pinB8 (brown wire) of the ECU.
Once the ECU receives the ECU request signal on that brown wire, the ECU outputs a ground on pinC2 (light green with a black trace) that goes to 85 or 86 (whichever wasn't used in previous step) on the A/C clutch relay.
The output of the A/C relay is a green wire direct to the clutch.
You may want to use a different power source to 30 of the relay instead of relying on power through the fan, thermostat & pressure switches to relieve them of the load i.e.pick up power from battery or another live fuse.

[hybrid]

↑ ↑ ↑ Thats why he gets paid the big bucks. ↑ ↑ ↑

[jas24zzk]

LOVE reading tech replies when boozed....will get right back to you when i draw it out


LOL

[jas24zzk]

Ok Great.

Green wire is 87.

I've got it wired Pwr in to the AC Req on the ECU so i have that part correct.

Mistake is clearly that I was expecting the ECU to send Power out and have wired it that way..direct to the Clutch. I figured out the Fan side sends ground, how i didn't realise the AC side was the same is beyond me.....maybe i was sober.

Thats an easy fix...i'll toss in a relay to manage it tomorrow.
I may also need to look deeper into the fan control. The ECU accomodates dual mode single fan, So I have it set up running dual single speed fans, with one mode controlling each. Just gotta check A/C mode is bringing in the bigger fan first

Thanx donauto.

[jas24zzk]

All fixed and working as advertised. thanx Donauto