air conditioning failure

This is a followup to an earlier post..the replies/answers were most helpful. However I'm not an AC expert and need some guidance regarding what I'm seeing.
It's a New Holland T4.75 tractor with 900 plus hours on it.

With AC compressor off .... I see green refrigerant(R134A) in the site glass on the dryer...it appears the level is just below the site glass.
When the AC compressor kicks in/on the refrigerant drops and I see bubbles for a short time. I can see the refrigerant but it's down a bit.during the compressor on cycle.
AC quickly pumps out very cold air
When compressor cycles off the green refrigerant comes back to original level.

Any Ideas from the experts.. do I have a low refrigerant problem?

Thanks

Measure suction pressure. Post back

I agree to check high & low pressures and report back. FYI refrigerant(R134A) is clear not green in color. Leak detector can be green in color.

A sight glass tells you nothing unless the system is running (compressor pumping). Bubbles for a few seconds is not abnormal. After it has been running and "warmed up" the glass should be clear which is a good indicator that your charge is up to snuff.

I don't remember what the original problem was. Does it cool at first, then shut off? It probably wouldnt start at all if the refrigerant was low. Can you get a set of gauges? Its pretty hard to diagnose an A/C problem without them.

Bought a T-6030 new in 2010 had the same problem it had to much refrigerant get your dealer on it

my pickup was doing the cold start then warm air. Local repair shop showed me the clogged rad under the hood. blew out the dirt and trash and WOW freezing in there. 2 cents.

I found your original post. I'm not sure how your condenser is mounted, but is it possible that it plugged up with some kind of trash and when you idled the engine down to open the gate, the trash fell off?

OK, here it is from an expert. EPA certified, been doing it for about 40 years, worked in dealerships for about 25 years, much experience.
First, the sight glass is NOT a level indicator. For that reason, it has been eliminated on most R-134a systems. It is ONLY relevant while the system is running with the compressor operating. Bubbles in the sight glass are normal with R-134a systems. You will not get a solid liquid line as you would have on an older R-12 system.
The real measure of your system's efficiency is the cooling and the pressures. You need to put a set of gauges on it. On an average 75 to 80 degree day, the low side should read in the 25 to 45 psi range. The high side should read from about 200 to 250 psi. If it is overcharged, the high side pressure will skyrocket to over 400 psi while the low side will read marginally higher.
The temperature differential should be around 40 degrees. At an ambient temperature of 80 degrees outside, the A/C should be able to get down to about 40 degrees. In a recirculating system (no outside air coming in) it will go even lower.
If your compressor is slowly cycling and the A/C temp in the cab is good, you do not have a low charge condition. Compressor "on" cycle will get longer as outside temperature increases. It should not "short cycle." The "on" cycle should last long enough for pressures to stabilize.

You need to put a set of gauges on it. On an average 75 to 80 degree day, the low side should read in the 25 to 45 psi range. The high side should read from about 200 to 250 psi. If it is overcharged, the high side pressure will skyrocket to over 400 psi while the low side will read marginally higher.

I think you are on the high side on your numbers but it taint nuttin to loose any sleep over... As for the skyrocket to over 400 psi my first check would be the airflow thru the condenser.

The "green" he is seeing MAY be a "no moisture in the system" indicator.

JF, you must not be familiar with R134A... if there's a sightglass in the system, NO bubbles means it's MT or WAY overcharged.

As another poster said, typically a sightglass in a properly charged R134A system will be bubbly/foamy/anything but CLEAR.

Thanks to all for the insight/education with a special tip of the hat to jimg from Allentown. My temporary "no-air" condition may have been a perfect storm of "conditions" .It's been hot, humid, dry and consequently very dusty in this part of New York State. My cabin filters, condenser, etc., were fairly dirty.... even though I cleaned them about 100 hours ago.. I suspect the system froze up and needed a few minutes to thaw out. The cabin blowers now seem to be pushing a bit more air. I'm planning on having the pressure checked by an expert as I don't have the proper "tools". It's been raining now for about 12 hours and will continue off and on for the next several days... maybe the dust will subside ..and more importantly, the grass/crops now can sprint toward a productive harvest/fall.

Thanks again for the assist...