juror

Subject pretty much says it all.
The A/C has stopped making cold air. Here's where things stand:

• The blower blows (as in, it functions)
• The compressor clutch is engaging
• Both fans run
• I hear a "hissing" sort of noise in the cabin, more or less continuously

The compressor, interestingly enough, doesn't seem to turn off. As I recall from last time, it should cycle on and off maybe a couple times in a minute? Probably depending on temperature, etc. I watched the clutch for a little over a minute, and didn't see it cut off.

The "hissing" noise isn't a straight hiss like a cat would make (or like letting air out of a tire). It sounds a little like somebody trying to play flute who hasn't a clue what they're doing. It's still predominantly a hiss though. Like on a scale of letting air out of a tire to incompetent flute playing, it's a 2.

Since the last time I had A/C problems, nothing has been done to the A/C. Other stuff that's been done:

• I did replace the alternator, which I realize is in close proximity to the compressor and receiver/dryer, but given that the compressor is running, I'm optimistic that I didn't damage anything up there with my big clumsy hands. Or at least I didn't bang anything in a way that created a leak.
• My posting history tells me that I had the downstream O2 replaced, but I think we can probably call that unrelated.
• Replaced the blower motor assembly. The old one was making noise.

Diagnostic equipment is limited to a DMM; I don't own a gauge set, nor would I have general knowledge of how to use such a thing if I did :-/

Is there any useful diagnostic testing I can do at this point, or am I taking it to the shop?

Thanks as always.

Slumpertcivic

juror

Don't we know the system isn't completely empty? Last time I had A/C problems, it was due to a hole in the system, and the compressor wasn't turning on. This time, it isn't turning off.

To be clear, I'm not claiming that the system can't be low, but if it is, it's in a window where there's enough R134 in the system that the low-pressure cutoff switch isn't disabling the compressor, but not enough to produce any cool air.

I'm also kind of looking for an explanation for the continuous hiss. As near as I can tell, that's new and showed up with the A/C no longer working. Is that a possible side-effect of a low charge, or is it possibly a symptom of another problem?

I'm reluctant to do a muggle's job of adding refrigerant without establishing how much is in the system with the proper equipment. I've read enough threads of people doing so and really getting themselves into a screwed-up situation as a result.

I should note that there's (probably?) dye in the system from the last time the A/C was inoperative. The shop added dye to the system when they determined that the condensor was bad. I know this because there's dye in a whole mess of places from that. Like the top of the battery. They're good guys, but maybe not as tidy as some On the other hand, they're generally willing to work with somebody who does some of their own work. Not all shops are.

I've been watching youtube videos all morning about automotive A/C diagnosis, and I think I've picked up a couple things about using a gauge set (which I don't yet own). If you'll all bear with me, this is what I've pieced together between that and looking at Majestic's parts diagrams:

When the compressor runs, it should lower the low-side pressure, and raise the high side pressure (obviously). The compressor is commanded on and off by the evaporator sensor, which I'm inferring is a temperature sensor based on some comments in other threads and the instructions for installing A/C on a vehicle that doesn't already have it., and will be forced off by a low pressure reading on the low side to protect the compressor.

We know that the compressor isn't turning off, which suggests a couple possibilities:

1. Slumpertcivic's low pressure hypothesis, and I have a really poor understanding of how this all works :-) Can probably confirm by waiting another week and observing the compressor not coming on.
2. Bad compressor (Would see no pressure rise on the high side or drop on the low side with it running)
3. Bad evaporator sensor OR control system screwed up. (A/C would blow cold, and eventually ice-up. Not the observed behavior)
4. Expansion valve stuck open (No rise in pressure on the high side, no drop on the low)
5. Low/no charge AND bad low pressure cutoff switch (If the compressor isn't bad, it will be soon )
6. Something else I'm missing?

Incidentally, the compressor clutch does disengage when the A/C button is turned off, so we know there isn't a short in that wiring.

Slumpertcivic

Slumpertcivic

ezone

Sounds like your freon is low.

Don't use stop leak. That **** can ruin the big expensive AC recover/recycle/charging stations us professionals use. I turn away AC work that involves freon on cars that have that in their AC systems.

juror

Thanks to both Slumpertcivic and ezone for the replies.

I've been trying to avoid just throwing more R134a at the problem because if the system is low, it means it has a leak (obviously), and the refrigerant has leaked out since the system was last properly charged (by weight, by a shop with a machine) a year ago. Having just replaced the alternator, my worry is that I would have knocked something loose in the compressor neighborhood and caused the leak recently.

I rustled up the last incandescent blacklight bulb in Boston a couple days ago (LED ones are like $15, wtf?) and checked things out last night. I can confirm that the system has been dyed. I see dye on the top of the receiver/dryer by the banjo fittings, around the top connection to the condenser, and on the same side of the condenser on the front.

I'm going to try pulling the bumper cover, cleaning up the dye (anybody got any better suggestions than brake parts cleaner?), then running for a few days to see where I actually have leaks. At this point, there's kind of too much dye everywhere to tell me anything specific.

If I end up adding R134a myself, I'll get the kind without stop-leak so as to avoid contaminating anybody's recovery machine in the future.

Thanks again, and I apologize for overthinking this!

ezone

Go ahead and strip the bumper cover off so you can see all areas of the condenser
Mix up some dish soap and water, I keep some in a spray bottle, (We keep a huge bottle of Dawn at work)
Run the AC system several minutes, (raises pressure in high side/condensor)
shut it off.
Immediately douse or spray soapy water all over the condenser areas where you found the UV dye. Wait a few/several minutes, see if you can find any bubbles forming somewhere other than where the hose and pipe bolt on (seams, tube joints, etc.). Reason, to make sure the condensor itself it not leaking. If it took several months to leak only a few ounces out then the bubble trail you're looking for is gonna be pretty dang tiny, if there is any at all.

If condenser is not proven bad, then reseal the line connections
Replace the O rings for each fitting where you found the UV dye. Both fittings on the drier. Use O rings that are correct for use with R134a. (some are green, but not always)

Not sure what to use to clean the dye off though. Soapy water will be on it, does it work?
I have lots of Brake cleaner in the shop so it's the next shot lol

juror

Update:

Circa ezone's reply, the compressor quit running at all, enough refrigerant having leaked out to set off the low pressure cutoff switch. I endured a couple weeks of putting up without A/C while my wife was out of town, during which time, I can happily report that I wasn't driving much.

I confirmed today that there was still R134a in the system by touching the low pressure valve and listening for a hiss. I'm pretty A/C ignorant, but I understand that if it were totally empty (i.e. all the R134a had leaked out and air had gotten in), adding refrigerant wouldn't work. Today I hit the parts store, and I can report that every can of R134a save the generic stuff comes with sealant. I said screw it, and got a can and a recharge hose. They were out of ones with a gauge, so I got one without, and went with the highly scientific method of slowly adding R134a until the compressor kicked on and the vents blew cold.

Because I'm not very bright, I didn't get a weight of the can and hose while it was full. Based on an equally scientific shaking of the can, I reckon I put in maybe 1/2 to 2/3'rds of a 12 oz (340 gram) can. So maybe 150-200 grams.

That's when I discovered that we don't have a spray bottle. Fortunately, I hadn't pulled the bumper cover off yet :-P

Further diagnosis will probably have to wait until later this week. In the meantime, at least I have cold air again, as I'm now commuting about 45 minutes each way to school.

Apologies for going about this in the most cowboy-*** way possible. I'm just trying to get to the point of being able to find out how big a problem I have. Once I think I have that fixed (if I decide to fix it; we might just live with it for the next few months), I'll take it to a real shop to get it vacuumed down and charged properly.

ezone

That was far more thought out and careful than most people just adding a full can or more then wondering why it still doesn't blow cold and now it tries to stall the engine when the compressor kicks on, or kicks on and off rapidly, or even vents clouds of freon out the high pressure relief valve.


If the freon you bought had DYE in it, that would be real helpful too

Slumpertcivic

juror

Progress update:

The system already has dye in it from when the condenser crapped out last summer. I've gone and cleaned the dye off of several places: the banjo fittings on the receiver/drier, the upper fitting on the condenser, and a couple of spots on the condenser. We'll see where it reappears and find out if I have one leak or several.

I'm happy to report that brake parts cleaner will remove the dye just fine. I feel like every time I use that stuff, I get cancer a year sooner. What a foul concoction.

I did pull the bumper cover off and spray soapy water on the places with dye on them while the car was running, but no luck getting bubbles. It seemed like the water was drying out before I had a chance to see any bubbles. Grrr.

While I was working on the car, I did some unrelated work renewing the zip-ties that hold the CVS solenoid valve in place (I noticed one of the original zip-ties dragging yesterday) and managed to drop a socket wrench on my face. Good thing I'm already ugly and married.

bbynams