Aircon / heater venting to windsceen, no vac leak at the rear of the inlet manifold

[QldKev]

Yet another VX with the aircon/heating air going to the windscreen all the time, without caring what mode the climate control is set to. I've checked the vacuum line on the back of the intake manifold and all appears good. No cracks etc, no hissing sounds. With the engine off if I remove the vac line after the one-way valve (side closest inside of car) I heard a hiss for a sec then it stops. If I start the engine with the line still off I hear a hiss. Putting my thumb over the vac line I can feel some vacuum. When I plug the line back in, no hissing but the aircon is still venting to windscreen (tried all modes for air out). I tried looking up under the dash, with the lower fuse panel off, and can't see up far enough to where it enters the car.

What could be wrong and where should I be looking now?

 

[BlackVXGTS]

Sounds like you may have a problem with your vacuum solenoid pack or with the vacuum tubes running to the solenoid pack:

VACUUM SOLENOID PACK
Located on the lower rear of blower motor housing, the Vacuum Solenoid Pack consists of a band of five electronically activated vacuum solenoids used to apply or remove vacuum to vacuum actuators to alter air distribution positions. Power is used to engage these solenoids and allow vacuum to flow to an actuator. Removing this power de-energises the solenoid and allows any vacuum contained in the actuator and line to vent
through the front section of the solenoid.
VACUUM CIRCUIT
Vacuum is used to control the ON/OFF functions of the vent modes and the heater tap. This vacuum is provided by the engine. The engine vacuum moves from the inlet manifold to a vacuum tank located on the HVAC unit. This vacuum tank is used to store vacuum in times when engine vacuum is low such as at full engine throttle. A check valve is fitted on the supply line from the engine inlet manifold. Through a black plastic vacuum tube the vacuum moves to the vacuum solenoid pack. This black plastic tube is also teed off to the vacuum control valve. From the control valve, vacuum moves into a yellow plastic tube and onto the vacuum operated
heater water valve. Vacuum is used to maintain full closure of this valve and no hot water can flow. As the ECC mode switch is selected electronic solenoids are activated in the solenoid pack causing vacuum to move to the desired vacuum actuator through different coloured plastic tubing. This vacuum will activate the vacuum actuator rod which then moves a vent position door. Fig. 2D-20 shows which vacuum actuators are applied with vacuum in a certain mode. Vacuum is vented from the vacuum actuator/plastic tube once the vacuum ECC mode switch is used to select a different setting.

 

[QldKev]

I may give it a play with this weekend, thanks for the idea of what next to try. Will post back how I go.

 

[QldKev]

Had a look today. Looks like the vac solenoid pack must be dead. I ran the black vac feed line straight into the white 'face' line and I have face level vents. I strapped it into place for now, and will look at another vac solenoid pack later. At least I have air con again. It's 3.30pm and still >28c, and it's not summer for another few weeks. Then the hot stuff hits. Once summer passes I'll have a look if the pack is serviceable or I'll just get a new one.

Thanks for the diagram.

Couple of links I found helpful (once I knew what to search for)
http://forums.justcommodores.com.au...changing-itself-98-vt-berlina-3-8-ltr-v6.html

https://forums.justcommodores.com.au/threads/how-change-aircon-actuator-vt.148796



QldKev