Alfa GTA Sportwagon

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Spantney

334 posts

154 months

Monday 4th July 2016
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Love this thread. Props to you for saving this one from the scrapper!

Glad to see you are going to sort it properly, are you going for a colour change if you get it completely resprayed or keeping it silver?


Backtobasics

1,182 posts

182 months

Monday 4th July 2016
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Great car, I miss my 159 Q4. GTA wings turn up on ebay from time to time, sadly the one on there at the minute is tatty and near side. They appear to be about £200 new

rxe

Original Poster:

6,700 posts

102 months

Monday 11th July 2016
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Right, this is going to be a fairly nerdy post about fixing air conditioning on a 156 GTA. The general principles will apply to most air con installations, but the specifics will be different.

When i got the car, I didn't try the aircon, as it was about -3 outside, and I was simply grateful that the heater worked. Inevitably the air con didn't work, and when I was changing the radiator, I found a big hole in the aircon rad, which would explain why. So after spending £80 on a new radiator, and popping it in, I set about getting the air con going.

The principles of air con are reasonably simple, and the same as a domestic fridge. You have a "working gas", it gets compressed which raises the temperature, the hot gas gets cooled in the radiator (or "condenser" which I just replaced), and then this cooled gas is allowed to expand rapidly in the "evaporator". The evaporator gets cold as a result, and the air is blown over the cold evaporator and cools you down.

So first thing is to ensure that your system is gas tight. There are a whole load of joints and seals that could leak, and if there is no gas, then you have no air con. The other problem is water, or humidity. Any water in the system will destroy it in short order, causing corrosion and ice blockages.

Thankfully there is a simple procedure that allows you to be reasonably certain that the system is gas tight, and to remove all the water - a vacuum test. You connect the system to a vacuum pump for several hours, which boils off any water in the pipework. You then leave the system under vacuum overnight, and if it is still under vacuum, then there are no discernable leaks.



The first tool you need is a manifold and hoses. Blue is "low side" - this is the feed into the compressor. Red is "high" side, the output from the compressor. Yellow is the hose used for vacuum sucking, or adding gas if you are a professional air-con bloke. I'm not a professional, I do it the way, see later.

Inevitably, the gauges read zero pressure at this stage - I'd just replaced the condenser. So connect up the vacuum pump to the yellow hose, open the red and blue valves, and let it run. About 40 seconds later, the gauges looked like this:



Yay, vacuum. If it goes to vacuum instantly, you probably haven't opened the valves properly, it should take a while to hoover out the whole system. If it doesn't go to vacuum, then you've still got a big hole in the system, listen for hissing noises. I left it like this for 5 hours which makes absolutely sure that any water in there is boiled off. This is much better than most garages can afford to do, if you get 20 minutes of vacuum, you'll be lucky.

After 5 hours of the pump chugging away, I closed the manifold valves, switched the pump off, left the gauges connected, and went to bed. Next morning - vacuum was still there. So good news - there are no material leaks in the system. There may be very subtle leaks that can be found with a pressure test, but this has a 99% chance of being good.

With a cleaned out and leak proof system time to give it some gas. The STP cannisters in Halfords have a bad rap, but if you've done the tests above, then they have a good chance of working. Fortunately for me, the amount of gas in a can is pretty much exactly what the system needs. I wouldn't advise just adding gas to a system using these cans - air con systems need a specific weight of gas, and unless you know how much you are shoving in, then you have the potential break something.

So, connect up your cannister using the cheapo attachment, and pull the trigger, with the engine running and the aircon switched to full demand:



What should happen is that the compressor should kick in, and draw the gas through the system. Unfortunately, it didn't. The pressure in the low side went to 60 psi at the first pull of the trigger, and that was it.

Hmmm. The compressor is protected by an electric clutch, which engages with an audible "clunk" when you switch the air con on. You can clearly hear this from the driver's seat, and it is the basic test of an air con system - no clunk, no aircon.

There are a number of things that can stop the clutch working:

- it can be knackered. Easy to test, there is only one wire on the compressor, and if you give it 12v, then the clutch should click in. Mine did, so it was working.

- there is a pressure switch that will stop the compressor kicking in if the low side has no pressure (all the gas leaked out) or the high side is over pressure (blockage). Do not bypass this pressure switch, it is there to protect the system.

- there could be electrical b0rkage somewhere in the circuit that is stopping it from working. Anything is possible on a 15 year old car.

To get the gas done, I just connected the clutch to 12v and let it run - I had gauges on the system, so it was safe. The gas flowed in, pressure on the high side built up, and lovely cold air poured from the dash. All good. With the can emptied, the mechanical side was done - 500 grams of gas in, all working.

So now it is time to work out why the compressor is not kicking in. You might be tempted to hard wire the compressor into 12v in the summer, or connect it straight to the demand switch on the dashboard - this would be a mistake as there the pressure sensor is there to protect it. If something goes wrong and the clutch doesn't disengage, it can shred the aux belt, which can then throw the cambelt off and it gets expensive very fast.

The pressure sensor is here:



There's not much you can do to test it, but the wires all looked intact and the connector was plugged in. If the sensor gives the OK and the ECU gives the OK, then these fire a relay that then switches on the compressor. The relays are in front of the battery:



Being an Italian car, the relay marked "Air Con" on the box was in fact powering the fuel injection, and removing that killed the engine. The one next to it (circled) was allegedly running the cooling fans, but was in fact the air con. Your mileage may vary. if I wiggled this relay out, I could feel it unlatching as it disconnected, and latching again as it reconnected. This was good - it meant that the ECU and pressure switch were fine - air con demand was there, but the signal was not reaching the compressor clutch.

Flipping the relay over and poking around with a multimeter revealed the following:



There was a 12v supply at the relay, so looking good so far. Following the brown wire, the next stop is a big multi plug in front of the relays:



All fine here, keep looking. Round the back of the engine is the next plug:



Here the brown wire (on the left), turns into a green and red wire (on the right), which is the same as the wire going to the compressor, so we're getting close. Again everything was fine here. According to the continuity tester, I had perfect wiring from relay to compressor. But continuity does not mean an ability to carry current - so measuring voltage showed that I had power all the way to the compressor plug. A quick wiggle of the plug (fairly fraught with the engine running and a hot catalyst about 3 mm from the back of your hand), showed that the plug itself was knackered - the compressor kicked in when the plug was pushed, and died when it was was released.

The parts car yielded a new plug, and this was soldered on with heat shrink to protect the joint:



With that fixed, it was all working - the compressor engaged with air con demand, the little light came on, and cold air was plentiful. Beers all found and felt extremely chuffed.

Edited by rxe on Monday 11th July 20:43

R8PJT

17 posts

94 months

Sunday 17th July 2016
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polished trumpets are very nice on these.

rdodger

1,088 posts

202 months

Sunday 17th July 2016
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Hi. Enjoying the thread.

Can I just ask is that a fuel line coming from the fuel rail to the plenum near the throttle body?

If so what's it doing? If not, what is it and what's it doing?

Oilchange

8,421 posts

259 months

Sunday 17th July 2016
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I have a 156v6, when it goes kapput will you fix it for me?

Usget

5,426 posts

210 months

Friday 22nd July 2016
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Enjoyed this read, especially the bit about the pick n mix fuses!

budgie smuggler

5,359 posts

158 months

Tuesday 27th September 2016
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Nice writeup, thanks. thumbup