AC dryer: What are you supposed to see in the window?
 

When I rebuilt my AC, I couldn't see anything in the sight glass. Today when looking, I could see it alternating between nothing and a moving milky something. What am I supposed to see in there? Is that what it is supposed to look like?

My understanding is you should see nothing. It should be clear and bubble free. If you see bubbles after start up and the AC has been on a few min it means the system is low on freon.

While it may show some things...
It is not reliable under all circumstances....
The MB Factory Shop AC manual does not recommend it as the final analysis for anything...
Only as a possible initial indicator to be followed by other things like gauge tests before actual corrective action is taken...

This is correct.

My refrigerant shows green in the sight glass because of the leak detection fluid added by my mechanic but the key is bubbles. More bubbles means less refrigerant. My '87 300D has a tiny leak (about 1 pound of refrigerant per year) in an expensive place to access, back by the firewall under the windshield wiper motor. I probably won't have it repaired unless it gets a lot worse.

Larry may have me on his ignore list...so he may not have seen what I posted....
What I said is STRAIGHT from the MB AC manual.....

I have the same question as the OP.

the car: 1993 w124 which is running on R-134a refrigerant.

the AC is still kinda cold, but probably not as cold as it was 3 yrs ago, i noticed a difference/decline in the cooling last summer.

Here is a video of the AC dryer window, after a short trip during which i had the AC on:
W124 AC DRIER WINDOW - YouTube

At the start of the video if you listen closely you can hear the auxiliary fans running at low speed, they continue to run until the 32 second mark in the video, a few seconds before the fans shut off, the AC drier window clears up completely, and remains clear until around the 39 second mark in the video, when you can hear the AC compressor reengage along with the auxiliary fans.

a couple of questions:
1)from 1-32 seconds & 40-1:01 are those what the previous posters referred to as bubbles? does this indicate that the system is low on refrigerant?

2) if i continue to use the AC, is there a chance that i can cause damage to the AC system?

3) would an evacuation and recharge be necessary ?

any suggestions or good info would be appreciated

thanks

You can't really use the sight glass for R134a. Your best bet is to hook up some gauges to your system to truly find out what's happening.



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Well Timmy's 93 model is a car that came from the factory with 134, so I'm not sure about the sight glass being useless. On a converted car, it is indeed useless. Even on an R12 car it is an indication but not a conclusive indicator.

Timmy, you need to get us pressures and temeperatures. Connect manifold gauges, stert car with a/c full on, set engine speed to 1500 or a little more, give it five minutes to stabilize and right down pressures, ambient temp and vent temp. That will tell the story.

Also while doing this it is best done with a high volume fan placed in front of the condensor.

The video isn't really clear enough to tell. Larry's advice is okay on this topic (but not his spelling, even that's blinded by his "rightness" or his penchant for homophones). The big fan in front of the compressor better replicates on-the-road conditions so your gauge readings are more accurate. If you have a shop do it, they should also do this, particularly if the ambient temps are high.

If you're going to check it yourself and it's R-134a you can pick up a low priced gauge set from Harbor Freight. READ THE INSTRUCTIONS AND WARNINGS!

On your model car the fans and the compressor share some switch gear so the low speed fans and the compressor cycling are probably related. M-B modified the designs from year to year, so you'd need to review the wiring diagrams in the EPC Startek site to verify their operation regarding turn on at low-/medium- pressures and temps. I'd recommend reviewing the FSM before doing any work on an unfamiliar system as a matter of course.

Maybe you're low on refrigerant and the pressure switch cut out the compressor, which also cuts out the fans, or maybe there's something else that's triggering the cycling.

With a functioning unmodified system the built-in safety features should protect the system from damage. If the pressure goes too high, a safety switch will cut off the compressor; if it's too low, likewise. If it ices over, it'll cut off. But if there's persistent cycling you could have increased wear on the compressor clutch. Minor, but possible, although I wouldn't characterize that as 'damaging the system.'

If/when you get numbers from a gauge set, I recommend this site for comparison: http://www.ackits.com/aacf/ptchart.cfm Notice that you can have a relatively wide range and still be "normal" in a -134a system.

So this is what it has come to? I can't even log in and try to help someone with their car without being insulted?

Timmy, feel free to PM me for help if you would like. I won't be posting in this thread just so that I can be insulted.

Man, why don't you get a life & leave the man alone...

He's not out to prove anything, just trying to help a fellow MB owner in need.

No debating that proper hvac technical analysis involves the use of gauges but if you don't have access to gauges some might try the sight glass method.

In my redneck part of the world its common to equate lots of small bubbles (milky looking) as the system being low on freon. Most times the compressor clutch is not engaging due to the low pressure so you don't see anything in the sight glass. Typically we'll jumper across the low pressure switch for a couple of seconds just to make sure the system will allow the compressor clutch to engage before spending the cash for the new freon. If the clutch engages remove the jumper wire and return the 2 wires to the low pressure switch. Next add freon from the small cans watching the sight glass. When it goes from "milky" (the system has now engaged the compressor on its own...jumper wire was just a quick test) to the occasional larger bubbles we stop adding freon.

Lot's of cars in my experience have slow leaks and adding a small amount of freon once or twice a summer will keep you cool without investing a lot of time or money. This is obviously the best case scenario if your a/c isn't cooling and if you have other system problems or a large leak then it takes time, money, gauges, analysis, etc.

Another red neck solution to a common climate control failure is when some of the vaccum pods fail such that your getting heat along with your a/c (if your a/c is actually working). Those pods aren't cheap and IMHO its a pain to access them then you have to try to determine which are bad. Instead of worrying with it, sometime in May I'll clamp off the rubber heater hose headed toward the monovalve so no coolant can get into the cabin whether the system is calling for it or not. In the fall I'll remove the clamp so heat can work again.

Again these are cheap easy work arounds (not true resolutions) that may or may not help your situation.

Good luck!

thanks to everyone who replied.

i'll try and post replies a little later on, when i have some more free time.
for now i would just like to add, that while making the video, ambient temps were about 80-85F. while reading the FSM i found a note that mentions that the dryer window sight glass is not reliable for diagnosing low refrigerant levels when ambient temperatures are above 35c/95F.



unfortunately i do not own any AC gauges. however, i can measure ambient temp(2inches from condenser) and vent temps using my DVM and i can post a higher quality video if necessary.