I own a 2004 Subaru Outback Wagon. Two months ago when my air conditioner was not working, my longtime mechanic told me that there was no refrigerant. He did a vacuum test and did not notice any leaks. He evacuated the unit and added the refrigerant along with a dye. Two months later the air conditioning is not working again. I took it back to him and he claims he cannot find any leaks. Any idea what might be wrong?
Apparently what is wrong is that your mechanic does not really have enough expertise to work on A/C systems.
If you take the car to an A/C specialist shop, they WILL be able to find the refrigerant leak that exists. Not all mechanics can fix all car problems. Sometimes you need to go to an expert, and this appears to be one of those situations.
I’m going to agree with VDCdriver on this one. You need an AC expert. The leak may be in a very hard-to-find location, such as the evaporator, but it’s pretty much guaranteed there’s a leak.
The dye was a good first step. The next step is to locate the leak. Then the leak can be repaired.
The valve for inserting the refrigerant may be leaking.