New addition! With a strange AC issue... Hissing sound?

[Fairtax4me]

Been poking around for a better car for the GF for a few months and she finally stumbled across one that was a trade in where she works (Carmax).

 

A nice 95 Legacy LSi. Leather, Sunroof, Auto trans, and very clean at 138k miles. Runs great, shifts great, drives great. $1400

 

Has the usual oil leaks, power steering leak, worn out steering rack bushings, might need an inner tie rod end, but the only weird issue is the AC.

 

AC seems to work, the compressor kicks on, it will sorta blow cooler air, but it starts making this strange hissing sound from the dash, sounds like from the general area of the air box. (Haven't had time to dig into it much yet) It starts about a second after turning the AC on. Starts out quiet and gets louder over about 10 seconds. Turn the AC off and it fades away over about 5-10 seconds.

 

Kinda makes me think the expansion valve has gone bad. Suppose it could just be a plugged evaporator though. Wondering if anyone else has ever run into something similar?

[Rooster2]

Refrigerant leak??

[Gloyale]

my 97 did the same thing.  Was told by the AC tech that charged the system it was "normal"

 

I didn't think so, but it has been like that for months and months, and AC still works fine.

[1 Lucky Texan]

have read several times of newer models 'hooting' when overcharged.

[Rooster2]

possible vacuum hose leak, or vac hose not connected somewhere??

[Fairtax4me]

It's way too loud to be a vacuum leak. If there was a Vacuum leak that large it would kill the engine. Plus nothing in the dash is vacuum controlled, It's all cable and electric.

 

Blower fan operates just fine on is own with no strange noises. Only when the AC button is pressed does it start making this hissing sound, and it gets loud enough that the radio can't drown it out. (At least not at a normal volume level)

None of my other soobs have ever made any kind of noise with the AC on, except for the click of the compressor clutch kicking on and off.

Her dad has a set of gauges were gonna hook up to it and see what's going on with the pressures when we get a chance. 95 FSM lists two different failure modes for the expansion valve (plugged valve, and stuck open valve) and approximate pressure ranges for each failure. Also has quite a few other diagnostics for various problems with the AC system. Should be able to narrow it down pretty easily once we get the gauges on it.

 

If I feel ambitious ill make a video of the noise and post it for edumacational purposes.

 

 

Which reminds me of the strangeness with the stereo. Factory original stereo, when you turn it on it goes to full volume on the left channels, but the right channel is almost silent until you turn it up to about 1/2. Adjusting the balance almost all the way to the right is the only way to bring the volume on the left channel down. Figure there has to be a short between the left and right channels or something. Not that it really matters because its gonna get a CD/Bluetooth upgrade very soon, along with some Polk DB651 speakers. And Ill be checking for continuity between channels before hooking the new stereo up.

[Fairtax4me]

Thought I might update this. A bit late but we did get this fixed. Expansion valve wasnt bad. The charge was so low that the compressor was actually pulling almost 20" vacuum on the low pressure side. The compressor was actually sucking refrigerant through the expansion valve and causing the hissing sound.

 

Put a can of refrigerant in it and the noise went away and it started blowing nice and cold.

Couldn't find any major leaks on it. Compressor was clean, no apparent leaks from the hoses there. Have been keeping an eye on the condenser looking for oily spots. I have a feeling it will be low again after this winter but maybe by then ill be able to tell if the condenser is going to need replacement.