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> AC functionality, 'world-of-the-strange...'
dante giacosa
post 11th August 2017 13:21
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1.4 16v
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So,

the other day, I was under the bonnet fooling around with the relays on the front of the battery.

I had taken the layout of these relays, as depicted in the manual, to be 'the truth' as opposed to the fiction which it really is, and had mistaken the one on the right for the Radiator fan 2nd speed relay.

(I now know this is the larger black square relay on the left)

Whilst trying to trigger this relay with a ground link (assuming constant positive, like the radiator fan relays) something else happened- I heard a couple of distinct 'clunks' from the other end (the belts end), of the engine. 'something' came in and out a couple of times.

It took me until later on to realise that what I had heard was the AC compressor (the engine was running at the time), and indeed the right hand relay is for the AC.

Now, I find this strange, as my AC doesn't work, yet.
I have verified 12volts at the green single way connector on the top of the compressor, when I press the button on the centre console (which illuminates), but nothing happens on the compressor.
None of the wiring on the right hand relay was a green outgoing line, so something else must be going on.

My question is- to run the AC compressor, is there only the On /OFF of a 12v line on that incoming green cable, or are there further electrical factors which affect the clutch on the compressor? Because I have never heard it engage, until this incident.

Or, is this a coincidence and that relay has nothing to do with the line to the compressor..?

I know there are high & low pressure switches, but if I had voltage on the compressor- shouldn't it just run..?

a schematic investigation starts now...!


EDIT- right; can anyone point out relay Q32, as it 'appears' to be inside the car..? Is it above the fusebox..? I now understand Q22 is the relay on the right at the front of the battery.

This post has been edited by dante giacosa: 11th August 2017 14:00
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Ganz
post 12th August 2017 22:58
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I think yours is a ph2. Not too knowledgeable on ph2 relays only ph1s. sure someone here will help.


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G A N Z 145

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dante giacosa
post 13th August 2017 07:08
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Thanks for that optimism, Ganz!

But, I might be out on my own on this one...
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shpuncik
post 13th August 2017 10:54
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By jump wiring relay you verified that your relay and A/C clutch both work.

But for the A/C system to work properly it has to be pressurized (refrigerant filled up). If it's empty or pressure switch is faulty A/C clutch won't engage even though A/C button will light up when pressed (at least on 145/146 it does). That's the basic principle of all A/C systems.

PS PM me your VIN number, I'll take look through wiring diagrams on what exactly you've got there tonight

PSS still haven't been to car for those ducting photos sad.gif
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dante giacosa
post 13th August 2017 22:06
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Oh, thank you, Valdas-

as it happens, after a full day down at the car; I had been under it three times by 08:00 this morning!- I am now safely up in the house, and am not planning on going out again at 23:00.

I've probably got a picture of the VIN up here, but I don't know where.

As I understand it; the AC is definitely pressured and holding pressure (verified by Alfa-specialist garage). I'm just a bit confused by how I could have had voltage on the compressor before (but no operation), and now, by accident it triggers.

The schematic shows how it all goes together, including a fascinating initial control loop through the cabin-vent fan speed control, so that if it is at OFF, the compressor could never come on..


anyway- thankyou for showing an interest- the schematic in question is 55-32, or page 20/3, by my reckoning. Everything appears to be there, but it doesn't explain my colour code jump, between relay Q22 and the compressor.

But I've owned enough of these cars not to take that too seriously!
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shpuncik
post 14th August 2017 13:02
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No problem Jim, I'm waiting for you to fire up your's A/C system so you could help me with mine wink.gif - still need to repair couple high pressure pipes.

When testing voltage it's better to use simple test light. If you have damaged wire multimeter could verify 12V and pass continuity test but bulb won't light up or will emmit dim light due to voltage drop.

As for the wiring diagram I think you should be looking into books 55-32A if you have manual A/C or 55-32B auto A/C.

If you're not stranger to MES you could use it to see maybe there are live data values in engine ECU like request for A/C clutch engagement, condenser pressure etc. And in case if you have automatic A/C there should be 3pin diagnostic plug for it too. At least in EU it's on passenger side bellow glove box.

PS Alfa wiring diagrams are simple - you should see French or Mercedes wiring schematics biggrin.gif
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dante giacosa
post 16th October 2017 09:08
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OK!

a bit of movement on this issue, as it happens.

At the weekend, I did the whole BBOB relay & fuse rewire on the group at the front of the battery. The AC relay (Q22) was in a very sorry state, and is now all good again, with a new relay base & contacts.

I now know enough about this to be able to see what is happening- but I need it explained to me.


Q22 has its coil fed by ORANGE (+) from the AC switch in the cabin, and by LIGHT-BLUE / WHITE (-) coming from the M1.5.5 engine management ECU.

With the relay removed and the AC button depressed- I can see a voltage pulsing on the coil contacts at the relay base- between 9 and 14 volts; every second or so. With the relay base plugged in; the compressor-clutch engages (!) and the compressor turns over, and then disconnects & stops, and then engages & turns over again, and then disconnects- every second or so.

It does this twice every time, and then remains disengaged.

Now, I don't think the AC button is having second thoughts on a 1 second frequency interval- but it does seem likely that the ECU is making a decision to remove the (-) feed.

My question is, along with the pressure switches (Q20) and defrosting thermostat (Q71), what could be telling the ECU to shut down the AC compressor...?

I think Ive got a good take on the pressure switch (Q20), see attached. But I can't actually see the defrosting thermostat (Q71)- any ideas where it is..?!

annoyingly Q71 isn't listed in the individual component breakdown, at the end of the AC section in the schematics



This post has been edited by dante giacosa: 16th October 2017 12:00
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Antonio
post 19th October 2017 21:23
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The anti-frost sensor is located at the low pressure side of the circuit, so, after the A/C evaporator. If I'm not mistaken, is near the drier filter. It can dis-engage the compressor if pressure falls below ~1 bar, if that occurs at idle speed, is mostly due to a lack gas on the circuit..also it would disengage it high side pressure is too high, mostly due to blockage in the circuit or fan not kicking in. Also if idle speed falls below a determined number of rpms, Aircon clutch goes off. I think easier way to know what's happening if to plug MultiEcuScan and there you can know why the clutch does that.


Remember both sensor have a check valve on the plugs, so can you can unscrew them without emptying the circuit.
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dante giacosa
post 20th October 2017 08:20
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Hey thanks Antonio-

as it happens; the car is facing the MOT next week, so I might get it checked out on the MultiEcuScan then.

Thats great to know that there is a check valve, to allow removal of both sensors from the circuit, without degassing.

I shall begin my efforts to locate the thermostat again.

yes- I didn't try to test functionality with the car actually running (driving) 'perhaps' that would have an effect on circuit pressure due to revs too...

thanks!
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