Hissing sound when ac is turned on
 

Hi everyone.
I have a slight problem with my air conditioning.
When I press the button to turn it on, there is a hissing sound for a few seconds, until the ac kicks in.
I should also add, there is a slight squeak when turning on the car, probably from the serpentine belt.
I say this because I did some looking and some people said that it might be the ac compressor pump.
However, I couldn’t find anything definitive.

Basically just before the evaporator (under the dash) there is a component that restricts the flow of liquid refrigerant, after this the refrigerant is released into a larger area to drop the pressure. This is where the cooling process happens, I would be very surprised if this process could ever be totally silent, certainly when you first start the a/c

There's a recent post on this. It's an early sign of low refrigerant due to bubbles in the expansion valve.

Please bear in mind that "flashing" can be caused also by a dirty condenser, so don't just assume low refrigerant in the system. Check the function of the components first. So many times low refrigerant charge is blamed for symptoms in an a/c system and it turns out to be bad house keeping.

Hi mate.
It’s not any flashing, it’s just a hiss sound.

I don’t remember hearing this hissing sound though until before a few weeks ago?

The refrigerant was refilled about 6 years ago, but it might have gone dry since then

You are dealing with a system that is running refrigerant around it, this is constantly changing from a high pressure gas to a liquid. I haven't seen a refrigeration unit that runs 100% quietly. The refrigerant would never dry up. If your system was "dry" it would have tripped out long ago on low pressure. If you have any concerns about the system please take it to someone who is qualified and registered to work on such systems and is on the f gas register.

had exactly the same issue on mine, it was low on refrigerant gas. I had it re-filled and tested for leaks (none found) but it came back after 6 months

anyway I ended up replacing the condenser as it was looking a little worse for wear, had it re-filled again and its been great ever since (nearly 2 years ago)

so yes, low on gas but you need to find out why there is no gas in the system. I strongly recommend getting someone check it for leaks

How can I check for leaks?