(another) A/C not working plea for help FIXED!!

Halcyon · 9 Jun 2018

More involved than the other topics as THERE IS NO LEAK!
Just wanted to make that bit clear - so there's no point in getting it re-gassed.
It's been pressure tested and there's plenty of gas in it.

The compressor isn't engaging (it isn't seized) there doesn't appear to be any power getting to the electro-magnet.

Unfortunately, My mate's expensive Snap-on diagnostic tool couldn't get any more info than my £3 eBay special so I don't currently have any code to work with.

I've been advised to check the compressor relay to see if the compressor does engage if I short it. Google tells me that the relay is behind the passenger seats.. could someone be more specific? Mine's a cab - does half the car have to come apart to get to it?

Something i have just noticed / double checked:
With the A/C set to LO only the off-side radiator fan is blowing. There's nothing from the near-side.
could this be what's causing the problem?

Thanks :thumb:

Alex · 9 Jun 2018

Your radiator fan problem is a faulty resistor on one side and nothing to do with your problem.

If no power goes to your electro magnetic clutch when switched on then I'd hedge my bets on it being a pressure sensor fault. If the sensor isn't reading a high enough pressure it won't let the compressor engage.

Also, my Dad once had a problem on his Saab with the aircon. It was fully gassed but didn't go cold. We tried everything and in the end it just started working. We're not 100% but reckon the expansion valve was stuck open and not creating a high/low pressure system so the gas/liquid wouldn't freeze/condense.

Have a go at tapping the valve as it could be that sticking and giving it a tap could fire the system into action, although I doubt it as the pressure sensor should still actuate the clutch even with the valve stuck open.

Halcyon · 9 Jun 2018

Thanks Alex - I was just looking at your link for the resistor from RS!

The pressure switch - that's the one in the front, just by the re-fill connectors, right?
could you point me at the location of the expansion valve? Giving it a tap won't hurt :thumb:

Alex · 9 Jun 2018

Valve, drier, pressure switch and refill ponit are all in the same place.

The valve is seen in this photo at the back, a gold coloured squared block between the yellow and green arrows.

deMort · 9 Jun 2018

With a fault like this then really its best to get a garage to use a tester and look at the sensor values .

if the car thinks its too cold either outside or inside the car then the a/c wont turn on .. no point in a/c when its below freezeing !

So a sensor fault or an electrical fault are the most obvious atm.

You could check fuses D6 and E7 .

You can download the wiring diagram from here ..

http://911uk.com/viewtopic.php?t=83491

My guess is either the interior temp sensor ( behind the round trim n/s ) or the pressure sensor .

Rad fan is as said a resistor and will not stop the a/c from working.

Edit ..

Its possible but highly unlikely the compressor clutch has failed .. you need to unplug the wire to the compressor and give it 12 volts .. you should hear a click if its working ok .

Halcyon · 9 Jun 2018

Thanks Alex, i'll give it some gentle persuasion. :thumb:

DeMort - I've checked the fuses and the look fine.

I probably have a way off logic about temperature sensors.. if it thinks it's -10c (for example) then wouldn't the heating be all to pot too? So if you set it to auto & 20c then wouldn't it just be going mental trying to heat the cabin as it would think that it wasn't getting up to temperature?

It's a 2 minute job to pop out the sensor and clean it though, so I'll do it anyway :thumbs:

Alex · 9 Jun 2018

Wouldn't think internal temp sensor would make any difference as you can run you aircon up at Hi (or eg. 28 deg c) and it'll just dry the warm air. If you switch you screen demister on, the aircon should also engage - have you tried doing that and seeing if it comes on?

Halcyon · 9 Jun 2018

***pops to the garage to check the demister function***

Halcyon · 9 Jun 2018

Demister didn't engage the A/C compressor, so air was ambient temp.

I've checked the air temp sensor and although dusty, wasn't clogged up:

and is this the pressure sensor? if not, what is it?

deMort · 9 Jun 2018

Interior and exterior temp sensors can stop the system from working if reading too low .

Halcyon · 9 Jun 2018

Ok.. So I need to get the system "read" to confirm that it's either the temp sensor or pressure sensor.. (I'm guessing these readings should be available with a PIWIS or Durametric?)
One of the sensors is over £250 so I may have to live without A/C for a while

I'll feedback when I've read the codes! Thanks guys! :thumbs: :worship:

Unless anyone knows what values I should see if i put a multi-meter on the terminals of the pressure switch?

deMort · 9 Jun 2018

Im afraid i cant tell you how to fix this but ill just say what i would do if i had the car in the garage .

i would connect a tester .. i would check the pressure sensor .. a reading of over 2 bar and it should work .. i would look at the values of all the sensors .. mainly to see if they are in operateing temp specs.

i would do a vehicle handover .. a reset of the cars control units .. a hard reset basically .

if needed i would check the feed to the compressor .. it should be 12 volts on this system .. its NOT on a 997 and onwards for anyone else .. thats a PWM signal which is different .

I may even give the compressor a 12 volt feed to see if it operates .. i cant tell you to do this though .. im responsible for what i do and cant advise this as its a total bypass of the system .

If there was no fault with the above then i would be looking at a control unit fault .. swop with a known good is the usual Porsche instructions for this .. etc etc .. that gives you an idea anyways

wasz · 9 Jun 2018

I think i once read the a/c sensor values with my £12 durametric clone tool

Halcyon · 9 Jun 2018

deMort said:
Im afraid i cant tell you how to fix this but ill just say what i would do if i had the car in the garage .

i would connect a tester .. i would check the pressure sensor .. a reading of over 2 bar and it should work .. i would look at the values of all the sensors .. mainly to see if they are in operateing temp specs.

i would do a vehicle handover .. a reset of the cars control units .. a hard reset basically .

if needed i would check the feed to the compressor .. it should be 12 volts on this system .. its NOT on a 997 and onwards for anyone else .. thats a PWM signal which is different .

I may even give the compressor a 12 volt feed to see if it operates .. i cant tell you to do this though .. im responsible for what i do and cant advise this as its a total bypass of the system .

If there was no fault with the above then i would be looking at a control unit fault .. swop with a known good is the usual Porsche instructions for this .. etc etc .. that gives you an idea anyways

Thanks :worship:
I've looked up the sensor and the pins are 0v 5v and variable 6v to 8v so I can borrow a volt meter and test that at least.

I've also ordered a PIWIS clone so I'll see where I get with that.
Might even get this fixed in time for the winter

Halcyon · 10 Jun 2018

pointless update!!!

turns out, it's a four wire sensor.
with the ignition on, two terminals have a voltage of 11.83v. one is 10.54v and the other is earth....

Sooo.. yeah.
no idea if that's any good or very bad! I'm impatient for this diag tool to turn up!!!

(another) A/C not working plea for help FIXED!!

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