Air conditioning

[85_Calais]

Just wondering, when a car air conditioning system "de-pressurises", where would you expect the hissing sound to come from?

I just had mine regased about ten days ago, and after I used it one day, I noticed a loud hissing noise coming from around the radiator / heat exchanger after the car had stopped. I phoned the mechanic, who said you can expect to hear a hissing sound as it depressurises, but I'm concerned that this may actually be a gas leak...any thoughts?

[commsirac]

sounds normal to me.

If the you can hear it leaking, it should have run out of gas by now!
Look for any tell tale oily residue around the fittings.

The hissing noise can come from several areas in the system as the pressure and phase changes stabilise.
Possibly the hissing in your system is coming from the receiver dryer which is typically mounted close to the radiator. It looks like a big can of fly spray. Follow the pipes that lead from the condensor, the thing that looks like a radiator that is in front of the engine radiator and one of them will lead to the can.

[85_Calais]

The receiver dryer looks to be OK.

I've got the feeling it has run out of gas...after ten days, but it's hard to tell at the moment as it's 10 degrees outside, getting down to two!

If I take it back to the mechanic, is there much involved in him doing a pressure test on it?

[commsirac]

No there is not much involved in doing a pressure test, takes 5 mins.

There should be a sight glass, either on the top of the receiver dryer or up near the fire wall where you should be able to see liquid refrigerant rather than bubbles.

Possibly suggest waiting until the temperature warms up and see if it really is working or not.

[85_Calais]

I had a look at the sight glass...should the liquid refrigerant be any particular colour? It just looks clear.

[commsirac]

I had a look at the sight glass...should the liquid refrigerant be any particular colour? It just looks clear.

Clear is good, if it has been charged with r12. Your car is designed to run with r12. With r134 there should just be the signs of slight bubbling when the system is running for optimum cooling, though my own tests have indicated it runs better on my car with the no bubbles.
Do you know what gas is in there, it could even be HC gas.
The refrigerant gases are colourless, they sometimes a green dye is added for leak detection.
Bubbles basically indicate the level of fill, lots of bubbles not enough gas.

[85_Calais]

i've got 134a (has been retrofitted), and the invoice says it has had a dye added.

Looks like I might be out of gas! It's going in tomorrow...

[85_Calais]

well...I need a new compressor...$1,200. Screw that!

:@:@:@

[Tom_1569]

Get one from a wreckers, or someone wrecking one. You will get one for 20 bux easy.

[85_Calais]

Well, the dodgy mechanic who told me I needed a new compressor was way off.

Took it to another place for a second opinion today - no leaks coming from the compressor, but there's a major leak in the condensor (like I said to the mechanic - there was a loud hissing noise coming from around the radiator!)

I guess it sucks that the first regas was wasted, but good news is the condensor is much less than the compressor to replace!

[commsirac]

I hope the 2nd mechanic knows what he is doing...... Did he show you exactly where it was leaking? Usually they leak at one of the fittings.
Were you not able to find the leak in the condensor yourself?
Would at least be going back to the 1st mechanic and asking for your money back for the regas service. A leak in the condensor would have easily shown up in the vacuum test and given that you could hear it would have been easily picked up by a sniffer that should have been run over the whole system after actually putting some gas in it. They may of course claim that the condensor became defective after the service, but most unlikely and was possibly the reason you were out of gas in the 1st place? You could also point to their diagnosis that the compressor was the culprit even when the leak was in the condensor as evidence that they must not have checked the condensor for leaks previously either!
Its hard going back and doing this sort of thing, but do it for the money and so they think twice about doing it to the next person. Possibly wait until another customer is in the office so it limits how nasty they try and get.