VS Air Conditioning Pressure Switch & Master Switch

[littlesprout]

Hi ppl

I'm having trouble finding a good wiring diagram for the air con pressure switch and the AC master switch.
I could find a few for vehicles fitted with climate control but none of standard air.

The pressure switch has 4 wires and I have no idea what each is for:
1) Green & Black
2) Black
3) Brown
4) Blue & White

Tomorrow I will be removing the dash fascia to get the AC master switch wiring colours etc.

If anyone has diagrams or knowledge of either it would be greatly appreciated!

[yoda69]

Have a look at viewtopic.php?f=32&t=1352

Light Green / Black - PCM AC relay control
Black - Ground
Brown - AC input request to PCM
Blue / White - AC pressure switch

V6 and V8 appear to have same colour wiring, but obviously different PCM so different pins.
Basically switch on dash requests PCM to turn on the AC relay.
The pressure switch activates the AC fan as required.

[littlesprout]

Thanks yoda69

I can't believe i forgot about these diagrams I was looking at these not two weeks ago...

What would be the best way to bridge the low pressure switch?? Blue/White to Black??

I wanted to just trick the system for a couple of seconds so I can test if the compressor clutch engages.

All help muchly appreciated

[yoda69]

Pressure switch operates the fan, you want to ground the light green/black wire to engage the compressor.

[littlesprout]

Thanks again yoda!

I'm very confused apparently...

I thought the pressure switch prevented the clutch from engaging when the gas pressure and therefore oil was low?

How does it do that if it controls the fan?

Does the pcm look for the fan being grounded before engaging the compressor clutch?

[yoda69]

When the switch sees a high enough pressure it activates the high speed fan, this is more of a protection.
There is also fan control through the PCM for normal operation, there are some differences between V6 and V8 in VS as I believe V8 still ran an engine fan.
The easiest way to engage the compressor clutch is pull the relay and bridge the pins directly if your only doing this for a quick check.

EDIT: sorry, your right, but there are 2 pressure switches, one for AC compressor and one for fan.
AC compressor is the Green/black, light green/ black is fan.

[pman92]

Looking at the wiring diagrams, the AC switch includes 2 seperate switches in 1 physical package.
1) Green & Black: power from fuse 22, through heater fan switch and A/c switch on dash.
3) Brown: To AC relay (Pins 30 and 85) and PCM (AC request input)

4) Blue & White: From cooling fan relay (86)
2) Black: Earth.

Operation: When heater fan and AC switches on dash are on, power will go through AC pressure switch from Green/Black to Brown wires. Brown wire supply's AC relay and signals PCM that AC is requested.
When PCM permits it, it will earth AC relay coil, and allow power through to AC clutch.
This is likely a 2 way switch (IE will open circuit if AC pressure is too low or too high).

2nd switch is a 1 way switch. When AC pressure gets high enough, Blue/White will be connected to Black. This earths cooling fan relay coil and cooling fans come on. (Cooling fans are not controlled by pcm for AC operation).

---
Later vehicles use a 3 wire AC pressure transducer (not switch), that tells PCM actual AC refrigerant pressure. PCM then controls AC and fan relays as required. IE. It's the PCMs job to cut out AC in under pressure or over pressure conditions, and turn the fans on once AC pressure gets high enough. This isn't the case with VS (PCM can only disable AC for full throttle/high rpm etc. All other AC electrical controls are conventional/old school)

[littlesprout]

Thanks you pman92 & yoda69!

That is exactly the info I needed!

The only AC diagrams I could find outside the ones yoad69 suggested are the VR/VS Max Ellery diagrams which aren't the best.

I was sure the pressure switch controlled the clutch for high and low pressure conditions but wasn't sure of the fan control aspect of the switch.

Can anyone confirm the earth point?

Thanks