VZ Calais Climate Control

[Philmecrackun]

Hi, still trying to find the intermittent fault with air conditioning not working, does anyone know where this sensor is fitted in or behind the dash, it is the cabin temperature sensor.

 

[diysv6]

View attachment VZ Alloytec AC dsecription01222015.pdf

I had some experience with my VT Berlina CC playing up some years back, and this is my take on how the VZ works.

The cabin temperature sensor is located to the left of the steering wheel near the Mode switch, and I think it has a small hole/ perforations to sample cabin air through the front of the dash.

Also a small air hose is attached to the temperature sensor which is connected to a thingy called an "aspirator tube" - which you have pictured in your query.
It has a special type of resistor whose resistance changes (NTC) with temperature. (Same idea as the engine temperature sensor). I think it is on the top right of the AC unit viewed from the front -

The aspirator tube has air passed through it at a certain rate. By Bernoulli effect, I think it's called, the cabin air is thus sampled continuously through into the aspirator tube. As the cabin air temperature changes, the NTC changes it's resistance values, which become the cabin's temperature signal. This signal from the NTC resistor is then fed into the control system for the AC unit. The temperature changes' signals from the cabin temperature sensor, then basically open or shut two mixer doors in the internals of the AC unit to blend cold/refrigerated air and the radiator's hot air to get the desired cabin temperature as preset by the vehicle's occupant/s.

Hope this helps you out.

edit Found some old diagrams - thanks to who posted them. typo fixed

 

[Philmecrackun]

Cool, thanks for that. I should have realised what that little vent on the LH bottom side of the instrument panel surround was, will tackle it on the weekend if it isn't a million degrees outside or raining.

 

[diysv6]

Edit: Locations for temp sensor clarified. The Aspirator unit is fixed behind the dash left of the steering wheel, found a reference to its location through a friend. I thought it was attached to the AC unit. The air sampling hose and the NTC resistor cable goes to the AC unit.

Have you tried using a hair drier/canned duster air (possibly coldish) carefully at the dash intake sampler point to see if the AC unit can be "forced" on/off gently in any way?
Can the AC be set as a manual unit? (Cannot remember my VT). Can you set to maximum cold at all? In the logics, the aspirator cabin sensor could be bypassed and out of the control circuitry.


There are three other sensors light, temperature and refrigerant pressure-

One in the top centre of the dash which detects sunlight and shade at the windscreen glass.

One at the radiator which gives the outside air ambient temperature.

I don't know if when either of these is faulty it stops the AC running properly.

Also there is an air conditioner gas/refrigerant pressure sensor switch somewhere which has some control over the AC units functions. If it is faulty perhaps its inhibiting the ACs operation?

Good luck with your searching.

A good scanner or a Tech2 could be a worthwhile investigative tool.
Haynes Manual #41743
P0532 AC pressure sig low
P0533 AC pressure sig high
P0645, 0646, 0647 - AC Compressor problems
P0691, 0692, 0693, 0694 - No1 Cooling fan circuit faults
There may be more but that's all Haynes have listed

 

[Philmecrackun]

When it does work, it works great, cold but not icy cold, all functions work, temperature varies by adjusting temp, it is just the compressor is not kicking in intermittently.
I can get in the car and drive up the coast and everything is great, then next minute, all functions are working but not cold, just ambient temperature air blowing out in your face or whatever function it is on, then switching it off then on, or just driving along it will suddenly start working again, which is real dandy up here on the north coast of NSW in summer. It is raining again this weekend so will check codes when it

 

[diysv6]

Is the compressor clutch OK? Maybe a loose, broken wire into the compressor connector or intermittent open circuit clutch winding etc.
If you can get the AC working when parked, and the fault comes on does the compressor clutch drop out then come back in etc? Usually the clutch can be heard operating.

 

[Philmecrackun]

I have a ELM327 bluetooth reader and a paid Torque Pro app(Android), just have to work out how to read codes and when it stops raining will check compressor connections again as it wasn't cutting in when faulty, I think it is an electrical connection fault hopefully.