A/C help please

[A80Avant]

Can someone tell me what does this solenoid valve does ?

http://www.ebay.co.uk/itm/VW-B3-B4-P...item439ff58620

its a valve that the vacuum line tree is connected to, and i am trying to figure out what some parts in the electronic climate system do, in order to pinpoint where my A/C problem exists.

What i am trying to figure out is which systems play a role in allowing the compressor to engage when asked to, IF we take for granted that the system is fully gassed, and the compressor engages when given a 12V power. Also the cables going to the compressor are checked for brakes and they are ok.

I have been told to look for the temperature sensor of the A/C system which i have found and will order and also ill look into getting a second hand control unit to test as well.

I am just trying to see what else i may be missing...

thanks

PS: i know it is not the kind of weather that i really need the A/C for,but its something that hasnd worked for a while and id like to solve it!

[johne]

That valve controls the recirculation flap vacuum actuator so isn't that important as far as the A/C is concerned. It's an open loop control so the climate control has no idea if the valve is there or working.

The recirculation flap and actuator are underneath the fan motor.

For the A/C compressor to engage the following have to be true:

The low pressure switch is closed.
The 2nd high pressure switch isn't open
The incoming air temperatue is warmer than approx. 3 degrees C outside - measured by the temperature sensor in front of the radiator. It's the same sensor that drives the display at the bottom of the dash so if that's showing a sensible reading it's reasonable to assume your sensor is OK.

There's more detail on what each part of the climate system does in the guide I put on here explaining how to convert to climate control.

John

[A80Avant]

What does the temperature sensor in the blower do?

sent using Android

[johne]

If you've got climate the system compares the temperature from the sensor behind the radiator with the temperature from the sensor above the fan and uses the average.

It's easy to tesk both sensors by measuring their resistance.

John

[A80Avant]

Is it possible that the sensor in the blower has failed and therefore the ac cannot engage?
What is the resistance I should be seeing?
The radiator sensor seems to be giving me correct readings.

sent using Android

[johne]

The temperature sensor above the blower is simple and very unlikely to fail.

Both temperature sensors should have a resistance of around 1000 ohms @ 25 degrees C, 2000 ohms @ 10 degress C.

John

[A80Avant]

i see.
i will try and check that, as i think the rest of the system is ok. Unless my control unit has a fault and doesnt allow the engagement to happen.

thanks

[johne]

In the guide I wrote and posted on here http://www.s2forum.com/forum/attachm...2&d=1283619204, Appendix C listed the fault codes you can read from the Climate Control ECU - you don't need VagCom or any external device. Through this interface you can see things like the temperature the ECU is reading from the external sensors and this may help you track down your problem.

John

[A80Avant]

i had checked the codes previously and the only one i got was for a thermostat sensor, but once i erased it, it didnt come up again.