Saab 92 Forum : Saab92x.com / Hissing from HVAC vents

Saavedro88 · 2012-07-09 14:30:59

When I bought my 9-2x Aero, it had a bad compressor clutch, nothing wrong with the compressor internally. It came with a new compressor, which I installed and had the system charged on the same day (system was open for maybe 10 minutes max = no accumulator issues). The A/C worked great for about two weeks, then one day the air coming out of the vents just wasn't cold anymore, and whenever the A/C system is engaged, there is a very loud, constant hissing noise coming from whichever vents I have the blower set to come out of. I have a sneaking suspicion that this means my evaporator core has started leaking, but I haven't smelled any freon. Figured I would ask before I tear the dash apart, Has anyone ever experienced anything like this before? I did some searching and found a few things but nothing exactly like what I've got going on.

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Linear Man · 2012-07-09 15:05:23

A normal noise. IF you searched, it's been discussed a lot. whoosh, hiss, darth vader in the dash will all yield results...

iamchris · 2012-07-09 15:07:17

It hisses the whole entire time the A/C on?

Saavedro88 · 2012-07-09 15:08:32

This is not the normal occasional hissing sound when the compressor activates, this is a CONSTANT hissing noise that doesn't stop until I turn the AC off. I couldn't find anything like that in the search...

Saavedro88 · 2012-07-09 15:08:45

iamchris wrote:
It hisses the whole entire time the A/C on?

Yes.

john_matrix · 2012-07-09 15:24:19

Snake in the dash.

Saavedro88 · 2012-07-09 15:27:55

john_matrix wrote:
Snake in the dash.

Not gonna lie, when it first started making the noise, that was exactly what I thought. eek

Scargo · 2012-07-09 17:18:53

makes sense, snakes don't like the cold...

Saavedro88 · 2012-07-14 20:06:15

Lol.

Alright. So I borrowed some AC pressure gauges from a co-worker and put 'em on the car today in between spurts of down-pouring rain. At Idle, my High side pressure was 100 PSI and my low side pressure was 10 PSI. When I raised the throttle a little, my low side pressure actually went into vacuum and my high side only went up to about 110 PSI.

Using my VERY limited knowledge of AC systems, I'm thinking this sounds like a low refrigerant issue? Can anyone back this up, or give me some more insight? Does anyone know how much refrigerant is actually supposed to be in these cars?

Saavedro88 · 2012-07-22 22:35:43

Well, after my first findings of low pressures, I decided to try to refill the system and see if it would help my situation at all. Bought me a can, hooked it up to the low side and let her rip. Before I could even blink, my LOW side pressure was up at 150 PSI, and my high side pressure wouldn't budge from 100. This was, of course, with the compressor running. Using my amazing powers of deductive reasoning, I decided my expansion valve must have gone bad, since the pressures wouldn't equalize, and the hissing sound I talked about seemed to be coming from that general location.

With the help of this guide: (http://www.clubwrx.net/forums/general-m … ost1582559) I was able to replace the expansion valve in about 45 minutes, not including the time I left the vacuum pump on the system while I put the tools away and ate dinner.

It might just be my imagination, but I'm fairly certain the AC is blowing colder now than it was before...

Hopefully this thread will be able to help someone else out in the future. Happy wrenching!

MetalNeverDies · 2012-07-22 23:03:03

How did you pull a vacuum on the system,

Saavedro88 · 2012-07-22 23:35:15

The guy at the desk next to me in the office had one. Looks exactly like this:

Hooks right up to the gauges, so it draws a vacuum from both the high and low side. It's really cool. And definitely a life saver. I wish I had known that he had it when I replaced the compressor instead of paying the Subaru dealership 212$ to do it. sadbanana