Loud hiss from Air Conditioner on 99 Silverado

My 99 Silverado produces a loud intermitant hiss from the engine compartment when the air conditioner (or defroster) is engaged. Sometimes the only way to get it to stop is to shut off the air. It happens in all weather conditions, cold or hot engine.

I got a 90 Silverado and I have the similar deal except I hear like water running through my vents and don't know what it is.

In regards to the loud hiss it's most likely a hiss in your Freon system. Does the air blow cold on a hot day? I know, crappy time of year to test it. I would figure you probably have a leak in your A/C system some where. Unfortunately, you'll have to get it checked by a pro.

As for the water sounds in the Vents it's most probable that your system is "LOW" on gas; your A/C system that is. Not a big deal just take it in and get it charged up. My 90' Blazer was doing that before I sold it. Wasn't a biggy as it ran fine and everything. Probably just a little on the low side for freon.

Hope this helps :D

As for the water sounds in the Vents it's most probable that your system is "LOW" on gas; your A/C system that is. Not a big deal just take it in and get it charged up. My 90' Blazer was doing that before I sold it. Wasn't a biggy as it ran fine and everything. Probably just a little on the low side for freon.

Hope this helps :DI'll try it. It's sounds like the engine sucking out the Anti-Freeze but I doubt thats it. I'll try what you said. Thanks.

This has actually been an annoyance for more than a year. The AC did blow cold last summer.

Sounds like it's most definately out of gas then

i wouldn't think that its low on freon because he says it still blows cold air and if its been leaking for over a year it would be out by now and the compressor would not engage or it would be atleast cycling on and off time after time ...... i would say that the orfice tube is prolly your cause but it sucks because you would have to drain all the freon in the system just to replace it i would take it to a air con. shop and ask them .... prolly give you a free answer and would do it alot cheaper than the dealer