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Air conditioning unit


Ady111
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Hello,

I have an, what I call, uncommon fault on my a/c system which consist of blowing hot air with the a/c ON, while releasing a strange smell and the aerator holes get wet with something oily. Sometimes for short periods the a/c works, but is becoming more and more rare. This conducts me to the idea that there is something wrong with the expansion valve or/and the evaporator. So I've took the decision to buy new ones and change them. My problem is that I cannot find a service manual where it's shown how to change this parts, or if there is an other way rather than to remove all the dashboard. If someone can help me with some pictures or information about the changing of this parts would be highly appreciated. 

The car is an 2012 Avensis T27 2.0l diesel with dual climate control.

Thanks!

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That sounds really strange to me. If something wet and oily is coming out of the vent (aerator holes ??) then you have to assume it is either coolant or some of the oil from the refrigerant... the problem with the latter is that any leak would reduce the pressure in the system which would render it inoperative. The system 'working sometimes' and having a leak aren't compatible with each other. If the system genuinely gets cold and operates some of the time then I wouldn't be suspecting the evaporator at this point. 

Is the drain hole OK and the pollen filter in good order (not disintegrating and clogging the air box up). 

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The filter is ok. I don't think it gets as cold as it should be. I suspect that the expansion valve is not working properly and has a leak. Why would you thin that it would be the evaporator? Would I have a headaching smell when the compressor stops if it would be the evaporator?

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You mentioned replacing the evaporator in the first post, and I wrote that it wouldn't be among the first suspects. You can get terrible smells from air con units that have stagnant water collecting in the evaporator housing. That water comes from the condensation produced, and if it can not drain away then it stagnates.

If the system gets cold then it hasn't a refrigerant leak. If it doesn't get as cold as it should then the most likely cause is that it is a little low on refrigerant gas (the system needs recharging). If it smells then it needs the drain hole checking and a suitable disinfectant product running through the system.

As you are unsure of the problems I would recommend you take it to an air con specialist who will be able to diagnose any issues and check the level of gas in the system. 

  

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Hello Mooly,

The fact is that I went to 4 air con "specialist", all of them sayed that the system needs recharged, all of them recharged the system, the a/c worked for 10-15 minutes, untill I left, and then again the same problems. This is why I want to take the problems in my heands.

I also got a diganosis tool and I saw that when the system is activated it's making pressure (16Bar) after it reaches the desire temp (5* i think) it shuts down (the compressor) and after this it is blowing normal temperature air. The system is then acitvated randomly and  without reaching desire temperature or pressure.

I sayed that I will change the evaporator and the expansion valve because the operation to reach them seems verry long so I wold not like to make it 2 times.

Can I chack the drain hole from the inside of the car? Where it should be?

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The drain hole is actually a tube that drains the evaporator housing to the outside word. If you lift the bonnet and then with the air con working you should be able to see water dripping onto the ground from around the middle of the car under the bulkhead.  

Is it possible the system has a leak that only opening up under a 'full charge condition' ?

If you have been to four different places and if all say that the system needs recharging, and if it actually worked for a short period after them doing so then that points to a leak.

I once had an Audi A4 (1995 model) and that suffered something similar. The air con failed and was diagnosed as low on charge and no obvious leaks were found. The system was only good for a few days after a recharge. It was really the final straw with that car and Audi but that's another story. I had a local air con engineer try a can of a special polymer sealant but again no good, the system would not hold a charge. The problem (I was told by Audi) was a leak in the evaporator and it was apparently not unheard off. The system retained a lot of pressure though.    

Replacing an evaporator/expansion valve (and the valve may even be part of the evaporator rather than a separate item as in older systems) is a major dismantling  job of the cars interior and dashboard and then the heater box. All the seals need renewing and re-assembling using correct procedures, otherwise it will just leak again.

If the system will not even cut in at all, then that to me suggests the pressure switches are not activated and the main reason for that is low charge. Those switches should be activated even with the aircon off and the engine not running. They monitor the system pressure when static, and there is also a switch that monitors for excess pressure when operations.

The definitive test for any air con system is to have the engineer couple it to a manifold gauge and look at the pressures. That instantly diagnoses most issues and if they did that and then said 'low on charge' then you have to take that as fact.       

    

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Hello Molly,

Thanks for your reply. This is also my point of view regarding the full chargte leak. I will also buy some gauges to monitor the pressures before starting to dismantle, and hopefully together with the diagnosis I will have a more clear view of the problem. I will buy also some orings, but hoped that it would be an easyer way to access the evaporator rather than dismantling all the dash (on my old opel I had only to remove some plastics to access it).

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One other thing comes to mind. If the system consistently works normally (but perhaps days apart... and you do originally say it blows cold air) but only works for a short time then another possibility is moisture within the system freezing and causing an obstruction. Now anything like that should be eradicated with a proper recharge which first of all involves pulling the system down to a vacuum and holding it there for 15 minutes or more. The vacuum causes water to have a lower boiling point and so the resulting water vapour is extracted.

If the system  has some unknown history and/or has had work done on the AC in the past with the possibility of moisture entering the system, then an extended vacuuming period of several hours would be needed, perhaps even with replacement of the receiver/drier being needed.

As before though, a proper diagnostic evaluation with manifold gauges should provide some clues.

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