All,

When the A/C is on in my 2003 XKR, there is a Hiss from the Center Vents that cycles on/off.

Is this the compressor turning on/off or something else? Is it normal?

A/C seems to cool fine with decent pressure (does have a slight stale odor).

Thoughts?

Thanks!
dsd

 

Is the A/C in the fully Auto position? If so, the air will be directed about the cockpit vents automatically by the A/C unit. Barring any problems with the A/C, the noise you are hearing is most likely the dampers opening and closing before cool air blasts from a different area of the car.

 

My first thought would be pieces of loose insulation in the ducts. The cycling sound is probably the amount of air at anyone time flowing over the loose insulation. There are a lot of threads about deteriorating duct insulation. You might try a good shop vac and put suction on the ducts and see what you get out.

 

I think that's exactly it. The hissing and the air corresponds (in auto). I assume this is normal but a cleaning couldn't hurt.

Thanks!

dsd

 

To learn more about your likely issue, google "automotive hvac servo motors hunting for correct position". Doesn't matter what brand of vehicle because they all work basically the same way....

 

I've never heard any hissing from mine. I use it in 'Auto' mode and, being in FL, it gets a good workout.

 

My car spent it's life garaged in the Seattle area, and then driven to another garaged area for eight hours and back, plus there is little need for the A/C in this area of the State most of the time, so mine was not exercised very much, if at all.

I bought it and moved it to the other side of the mountain, and the other end of the Weather Spectrum as the Eastern side of the State, where I live, has a Desert Climate. Unlike Seattle, we have the 'Text Book' Four Seasons, as far as a mild Fall, snow in the Winter, though it can get very cold with temperatures in the negative and I personally will not attempt to start my car if it is 23 degrees F or less outside, but we normally see temperatures in the 100's and up, during the Summer months.

Another good indication that the A/C was not heavily used when buying a new, used car is when you turn it on Maximum A/C, and dust blows out of every vent. That is what happened to me, and I noticed a few strips of foam Weather Stripping ejected from the Center Console Vent, along with the dust. A larger piece of foam actually had an impression permanently pressed into it from the Damper Plate constantly being in the closed position due to lack of use.

After using the A/C a few times, and the larger piece of foam was ejected from the Center Console Vent, is when I started to hear a slight whistle as the Damper Plate closed to seal, which turned more to a 'hiss' after it was fully closed, and the air flow was directed to the Lower Console Vents, but it is only noticeable when the fan is on high speed in my case.

 

I've also encountered a lot of times when the refrigerant level is low that there's also a hissing noise coming from behind the dash. The noise is coming from the expansion valve when it's low on Freon. Just a thought if you haven't come up with a fix yet.