Interpreting sight glass

strother · 06-03-2005, 04:16 PM

I'm trying to find out how bad my A/C situation is. In my 82 SC, the sight glass is behind a yellow screw off cap in the receiver/dryer (I think), located in the driver side front wheel well. When I turn the engine on and the A/C on full blast, I don't see much going on in the sight glass. There is a little pale yellow ball in the sight glass that just sits there.

I don't see streaking and I don't see bubbles, but to be honest, I'm not sure I see any freon there, either. If there was freon, would that little ball flutter around?

strother · 06-05-2005, 07:34 AM

Gotta bump this question back up to see if anyone has an answer...

asphaltgambler · 06-05-2005, 07:37 AM

If all is good you should see almost nothing, occaisional cloudy mist going through, that's it. Any more than that it is probably undercharged or too much vapor, not enough liquid freon.

strother · 06-05-2005, 07:50 AM

I see absolutely nothing except a lifeless, pale yellow ball. Bentley doesn't mention anything about there being a ball in there, but I suspect it was put there so one could observe fluid flowing. To be honest, I have no idea.

911pcars · 06-05-2005, 03:33 PM

If you see absolutely nothing, that probably means the system is completely full or completely empty.

At any rate, manufacturers no longer rely on (or use) the sight glass to diagnose the system. If the system isn't producing cold air, they connect a pressure gauge or recycling machine to the system and diagnose. Refrigerant is too expensive to diagnose by trial and error.

And if the sight glass showed some bubbles, there is only way to ensure the system operates at maximum efficiency; by using the correct quantity of refrigerant. The only way they can do this is by removing and recycling what's was in there and installing the correct amount; no more and no less.

Unless you can install a new receiver/drier, connect pressure gauges to your system, evacuate the system with a vacuum pump and charge with refrigerant, I'd leave it to an A/C shop.

MHO,
Sherwood

dfink · 06-05-2005, 05:36 PM

Yes the ball is there so you can tell if fluid is moving with out the ball a full system looks empty. But all the other answers are correct you should probably take it in and have it checked out. Might just be out of freon. If it is totally out I would think you have a leak somewhere. If it is a slow leak the shop will put in a dye that they can use to later locate the leak.

tommy5305 · 06-05-2005, 05:52 PM

Does the clutch engage, does it blow cold? If not, Its probably empty.

strother · 06-05-2005, 06:39 PM

Thanks, everyone, for the info. It's always been my plan to have a professional work on the A/C -- I was hoping I could diagnose the extent of the problem, so that I could schedule how long my car is away and so I could be prepared for the money to vanish.

How does one know if the clutch has engaged? FWIW, my air does not blow cold, but it does seem to blow cooler than the ambient temp.

tommy5305 · 06-05-2005, 07:00 PM

Look at the FACE of the comp. If it is spinning it is on. If it cycles on and off you might be low on freon

kuehl · kuehl's Garage

There where many thoughts on reading the driers with the ball type site glass. Typically the old rule was \\\"as you are filling the system, and the ball just starts to float and rise to the top, you were full\\\".

When you have a site glass that does not have a ball then you are looking for refrigerant. In that case you would fill the system and stop when the site glass was full of refrigerant.

The problem with either interpretation, as noted or posted in the thread, is that that concept can be difficult to read on either type site glass (with ball or without). When the ball type site glasses were picked for the car the type of refrigerant at that time period was R12. If you are using R134a, for example, you can disregard looking at the ball or looking at the site glass all together because you are more interested in the high side system pressure.

You are better off using what is called the P&T Method, which means Pressures and Temperatures. To do a P&T the ac tech notes the ambient or outside air temperature. This ambient temperature is cross referenced to a refrigerant chart for your particular type of refrigerant. Along side of the that specific ambient temperature will be a \\\"suggested\\\" high side pressure value, which in theory is near perfect (in theory mind you) for that given ambient temperature. So if the ac tech is comfortable with P&T charts then you should do OK in getting near a good refrigerant charge.

In most likelyhood your car does not have a high low pressure switch (started with the 964), therefore your compressor clutch can still engage with a low refrigerant charge. This is not good by the way since your compressor gets its lubrication from the refrigerant and oil mix that flows through the system.

So in the mean time until you see your ac tech, locate the clutch wire coming from the compressor. It will connect to a female spade terminal near the oil filter. Unplug the connection. This will prevent the clutch from engaging until you get it serviced. Don\\\'t forget to advise the ac tech that you have done this.

911pcars · 06-05-2005, 09:24 PM

BTW, don't allow the A/C tech to insert any dyes in the system. Reasons:

- Dyes usually include refrigerant oil (sometime a "stop leak" solution). Both take up space inside the system and reduces the volume available for refrigerant.
- If there are leaks inside the vehicle, it will stain upholstery fabric and clothes. If you're into retro parties, dye-stained clothes are visible under a black (ultraviolet) light.
- Electronic sniffers are cleaner and more sensitive

Sherwood

strother · 06-07-2005, 01:06 PM

Took it to the shop, and all it needed was some freon. Cold air now. By the way, the pale yellow ball FLOATS in the freon, even when the A/C is off. If you look at the pale yellow ball and it is lifelessly sitting at the bottom of the sight glass, your system is (like mine was) empty of freon.

kuehl · kuehl's Garage

Quote:

Originally posted by strother
Took it to the shop, and all it needed was some freon. Cold air now. By the way, the pale yellow ball FLOATS in the freon, even when the A/C is off. If you look at the pale yellow ball and it is lifelessly sitting at the bottom of the sight glass, your system is (like mine was) empty of freon.

Good for another season?

strother · 06-07-2005, 03:09 PM

I dunno. Here in Houston, the A/C season is 10 months.