Air con pressure switch test - Alfa Romeo Forum
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(Post Link) post #1 of 5 Old 06-06-05 Thread Starter
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Air con pressure switch test

Can anyone tell me if it is possible to test the pressure switch on my 156 aircon? The switch is attached to an aluminium cylinder which is located low down under the front of the drivers side wing. At 40+ I would like to check it first! The a/c has been recharged and I have confirmed the a/c switch on the dash is sending a feed to the pressure switch. As I suspect it will need changing is it possible to remove and replace without draining the a/c?
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Temporary Noble
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I have same issue.

You can't change the switch without draining and refilling.

I'm pretty sure it's the switch as the ECU says there is 0bar when I connect the car to the fiatECUscan software. I've had my AC mate attach pressure clocks and there's plenty of pressure there...

I've bitten the bullet and ordered the switch from partsgateway for 42 delivered... My mate will have to fit, in order to drain and refillt he system...
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Sadly you will need to recover the refrigerant before you change the switch. It is very unusual to isolate such items on automotive applications. However once this has been done you can still check the switch operation using Nitrogen, which a good aircon company will be able to do. Bad news is this will probably cost 40 before you know if you need a switch as well!!

If Temporary Noble is correct and the ECU measures pressure then this is a bit more than a switch and looks like a bargain at 40!!! Hopefully we are all talking about the same apples?
Temporary Noble
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I've ordered the part so will update with pics and ECU readings when it arrives...
Temporary Noble
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OK, time to update on this AC issue.

The new pressure switch eventually turned up, it can be fitted without loosing any gas, there's a valve underneath which it opens as you screw it in.

It looks like the AC pressure feature in fiatECUscan doesn't work, as the new one also reads 0bar, so this seems to have been a red herring.

We started tracing the connections back from the compressor - the relays in front of the battery were all mixed up - the AC one turned out to be the one with a white plastic cap over the main block, with very small holes that we couldn't get the multimeter through! As they unclip, we could check underneath (I also rearranged them to match the diagram on the cover)...

I found that the supply side of the relay had no power, but the ECU / switch was switching. I don't know where the power to the relay should be coming from, the 40A fuse at the back of the battery is OK.

So, in the end we simply ran a wire from the battery to the relay, via a 10A fuse.

The AC now works fine, and switches on and off with the original dash switch.

On the subject of the pressure switch, if you loosen it with the compressor running, it knocks off the compressor...

Anyone want to buy a new pressure switch???!!!

The AC is now very cold, soon after startup.

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air , con , pressure , switch , test

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