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Discussion Starter #1
Just wondering if anyone's got any pointers before I go down the searching for a broken cable route...

Bought my GT earlier in the year and the air con didn't work. I found a receipt from a garage saying there was a hole in the condenser from mid 2015 so it hadn't worked for at least two years. Anyway, I fitted a new condenser and had it regassed/serviced and all was well - no leaks and the air con worked.

Roll on a couple of weeks (I was fixing various things so it hadn't been driven) and the air con had stopped again. A couple of weeks after that I moved house and after the 45 mile drive I realised the air con was back! Unfortunately, this was short-lived and it hasn't worked since.

I've put 12v direct to the compressor and it works/gets cold so that's ok. I've also checked the pressure and was surprised to see it was still pressurised. So the only thing I can't find is the pressure switch, so can't bridge it to see if it's that. Does anyone know where the pressure switch is located? Any other info like pin-out diagrams would be handy or if anyone's got some other pointers, it'd be most appreciated.

Thanks in advance,

Neil
 

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You should be able to figure out where the pressure sensor is by checking Eper. It's screwed into the top of the separate dryer on my 156 (behind the left hand foglight as you look at the front of the car) but no idea if the GT is laid out the same way.

There's a post towards the end of this thread (https://www.pistonheads.com/gassing/topic.asp?h=0&f=47&t=1586367&i=40) which runs through a hunt for a dodgy connection, it's a 156 GTA rather than a GT but the general principles should help. Also this thread has a fair bit of detail on wiring arrangements which may help: http://www.alfaowner.com/Forum/alfa-gta/1082922-air-con-saga.html - same qualification about it being a 156 applies.

So I don't have an answer I'm afraid, but hopefully that may help you locate one!
 

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Thanks for the replies, it does seem to be one of those niggly faults to find.

I?ve just removed the T05 relay and bridged the switch terminals and the compressor?s kicked in straight away but this seems to bypass the demand from the climate control unit (stays on when not selected). So without a diagram I?m a bit baffled as to what this is telling me... Is the pressure switch ok or not..? Oh the joys!
 

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Thanks for the replies, it does seem to be one of those niggly faults to find.

I?ve just removed the T05 relay and bridged the switch terminals and the compressor?s kicked in straight away but this seems to bypass the demand from the climate control unit (stays on when not selected). So without a diagram I?m a bit baffled as to what this is telling me... Is the pressure switch ok or not..? Oh the joys!
I'm assuming when the compressor kicked in with the relay bridged the only route for power to get to it was with the standard wiring, i.e. you didn't have a separate direct feed to the compressor as you did with the earlie rtest you'd done? If that's right, then I think what you've learned is that wiring from the relay to the compressor is ok, so dodgy plug on the compressor is not the issue. Admittedly it may not say anything about the pressure sensor, but at least you've ruled out one potential issue!
 

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I'm assuming when the compressor kicked in with the relay bridged the only route for power to get to it was with the standard wiring, i.e. you didn't have a separate direct feed to the compressor as you did with the earlie rtest you'd done? If that's right, then I think what you've learned is that wiring from the relay to the compressor is ok, so dodgy plug on the compressor is not the issue. Admittedly it may not say anything about the pressure sensor, but at least you've ruled out one potential issue!
I'm on my fifth night shift out of seven and it's funny how things don't compute for me in the day now but in the middle of the night they do! You're absolutely right about the wiring, the supply to the compressor is separate to the control circuit with the pressure switch, so when i bridged the terminals that would otherwise be bridged by the relay latching, the compressor would start regardless of the demand from the climate control :party:

Ok so at least that rules out that section of the circuit. Think I'll bite the bullet and remove the bumper to get at the pressure switch. Then if I bridge the correct pins and the compressor kicks in, at least I'll know it's just the pressure switch.
 

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so when i bridged the terminals that would otherwise be bridged by the relay latching, the compressor would start regardless of the demand from the climate control :party:

Ok so at least that rules out that section of the circuit. Think I'll bite the bullet and remove the bumper to get at the pressure switch. Then if I bridge the correct pins and the compressor kicks in, at least I'll know it's just the pressure switch.
Yep, you're essentially bypassing the "thinking" side of the system and deciding for it that conditions are ok to send power to clunk the compressor clutch. The elearn extract linked in one of those other threads puts it in slightly more technical terms, but fundamentally that is what's happening.

There is an aircon module in MES, although I think it's only in the paid option. I don't know if that might enable you to see the status of the pressure switch without needing to remove bits of car to get at it.
 
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