AC makes weird noises

My air conditioning makes a noise that sounds like some kind of pump under the passenger side of the dash. It's really loud and annoying. I've had it to a Buick dealer who said they couldn't hear it (???) and I've had it to a local garage several times and they can't figure it out. It continues to make this noise long after you turn the air off. It doesn't do it when you use the heater. It's a hard kind of noise to explain but it is really driving me nuts! Can anyone help me with this? Thanks.

its kind of like a hiss? This is normal. How AC works is by shoving high pressure refrigerent through an orface. When a fluid goes through an orface, you get a pressure difference and the orface will also slow down the flow of refrigerent. So when you have the AC on, there is a compressor that circulates the refrigerent thought the system and one one side of this orface you have something like 150-200 PSI and on the other side of the orface you have like 30 PSI. Well when you shut off the compressor, the pressures between both sides of the orface equal out. What you are hearing is the two pressures equaling out. It if very normal.

I know I went into it more than you probabally wanted but, if you are interested in knowing how it works or, I have confused you anymore, jsut ask and I will try to explain better.


Welcome to AF

Andy

Andy,
Thank you so much for replying. No, it's not really a hiss. It hasn't always done this or I would think it's something normal like you've explained. It is so loud I have to turn the radio up really loud to not hear it and it does it the whole time the AC is on and long after it's off. It does sound like something trying to push something out (sorry, I'm a female--it's hard for me to explain car noises!) Let me know if you think you can help me anymore. I'll even tape it and send it to you!!

your orface tube could be partialy plugged causing higher presssure and maybe some compressor knock. It's hard to tell without being there and having AC gauges hooked up.


I would be suspicous of an orface tube. What year is your car?

It's a 1996. Thanks again!

A month later- is it still making the noise? If so, I have some suggestions.

Yes, unfortunately. I have had other things to tend to and haven't had the time or money to have it looked at yet. It's cool weather here now, but every so often I've used the AC on a warm day and it still makes the noise. Believe me, it's not going to go away on its own! I'd appreciate any help.

If it happens only when the blower is on, and especially if it's louder as you move the blower (fan) to higher settings, it could be that something has fallen through the ducting down to the blower, which is directly behind the glove box and almost at the lowest point in the system.

In other cars I've had pine straw and leaves make their way thru the screens under the hood right in front of the windshield, and lodge against the blower blades. I had a field mouse get into the ductwork and fall into the running blower- but the smell was a giveway.

On my Riviera, I started having water on the floor in front of the seats, and a bubbling, gurgling sound that everyone told me was from the power steering pump and return line in the engine compartment in front of glovebox. Various power steering repairs were recommended.

Finally I realized that it often occurred or got louder when I turned left or stopped suddenly. What I discovered was that the rubber drain tube on the air conditioning, which is like a rubber duck's beak under the system and directly behind the back of the engine, had clogged up with residue from A/C condensate, which is not uncommon.

The condensation water from A/C had filled up the condensate tray, and spilled over into the blower, which is mounted vertically at the bottom of the system and behind the glove box. The blower would swirl the water as it ran, and make a steady gurgling sound like fluid moving thru a pipe with lots of bubbles. If I turned left, the mass of water would shift to the right and go into the blower. When I stopped suddenly, it went into the blower. Turning right pulled the water away from the blower, and hence, no noise.

I had to replace the blower (about $60 at Advance) as it was all corroded from the water, and I removed the rubber beak drain from the condensate tray and replaced it with 1/2 inch copper elbow pointed down. Now the A/C drains condensation out profusely every time the car is parked, the new blower is quiet, and the weird noises are gone!

It continues to make the noise long after the air conditioning is turned off. It guess what it sounds like is a pump. I appreciate your suggestions and will have someone check them out for me as I have no idea how to work on a car! Thank you for your help.