AC / R134 / Sight Glass - PeachParts Mercedes-Benz Forum

davidmash · #1 05-01-2010, 08:43 AM

I had the 190 converted a few years ago to R134. It has been cooling fine till recently.

The compressor turns on and it cools for a bit then shuts off. Comes back on a while later. If I shut down the engine and restart the compressor will come on as well.

I popped the hood and noticed when I had the engine idle with the AC running, the sight glass had some bubbles in it. Quite a bit actually. I thought I remembered reading if the pressure was not not right, it could cause the system to shut down.

I was planning on taking it to my indy to have the system charged. Does it sound like I need to be looking for something else?

Thanks

Spetz · #2 05-01-2010, 09:03 AM

If it has bubbles it means that it's low on gas.
Get it regassed (as well as vacuum leak test etc)

I had mine done 2 days ago, and now at idle it produced 8 deg C air with ambient temperature of 32 degrees C.

samiam44 · #3 05-01-2010, 01:08 PM

site glass for a converted R134a system is not accurate. Use temps and pressures.

The compressor is suppose to cycle with cooling demand. If it cuts out and requires turning the key off/on to allow it to cycle again- then it could be an oily compressor clutch. I spray mine out with brake cleaner.

M

macdrone · #4 05-01-2010, 02:44 PM

Low on gas definatly. Not a huge difference except at idle from 12 to 134 in these. The evap is so small. I put a small can of stop leak in mine for good measure just because the evaps are so hard to replace.

#5 05-02-2010, 07:41 PM

Your system is failing just as statistics show for a converted system. Statistically an R12 system converted to 134 fails in two years.

As Samiam says, the speed sensor trips out the clutch in the event of slippage in either the belt or the clutch. If you don't find a reason for speed sensor tripping, start by using manifold gauges to check the refrigerant charge.

macdrone · #6 05-03-2010, 09:24 AM

The evaps on these spring leaks also you could use dye and then check the drain under the car to see for sure as the evap drains on either side of the transmission.

#7 05-04-2010, 07:26 AM

The 190's are not prone to the same evaporator failure rate as the 124 chassis cars. Even if it WERE a 124 chassis car, assuming an evaporator leak is quite premature. Also in spite of what some people say, they do NOT ALL fail. My 88 300E still has the factory evaporator.

dstorey · #8 05-04-2010, 08:11 PM

The mention that 134A conversions fail. The problem with conversions is that while 134a approximates R12 it is less effecient and a system not designed for it has less margin. The other problem is that 134 uses different oils than r12 and needs different seals. So what everyone does is replace all the o rings with nitrile or something that is compatable with the oil forgetting that there are seals in the compressor. Also all the old oil needs to be flushed out and a new receiver dryer installed

davidmash · #9 05-17-2010, 12:35 PM

Seems like the culprit was a loose shrader(sp?) valve. Tighten it up and put in 2 lbs of R134. one third of a pound stayed in the lines so the system ended up with 1.7 lbs. Cools very nicely now and all is good in the world.

MB dealer did the conversion a few years back. I am friends with the senior tech and the shop manager and I trust them. They have save me tons of money by doing things that others have said they could not do. Wife had a trans valve leak. Everyone said the trans had to be dropped to access it. The senior tech said he was pretty sure he could do it with the trans in the car. He was right ... and the list goes on.

Any way, they did the change over to R134 and I do not notice a difference in cooling. The car can still keep me comfy on a 105 degree TX summer day. R134 is better for the environment and at the time it was less expensive so I have no regrets about the swap.

#10 05-17-2010, 01:13 PM

David,

Glad it worked out. What does the site glass look like now? The sight glass is usually useless in a converted system.

I did not notice earlier that you are in Grand Prairie. I graduated high school in Grand Prairie. My Dad died in January but my Mom still lives in GP.

Which dealer do you use? My Bro in law is a Tech at Mid Cities.

Larry Bible
GPHS Class of '67

#11 05-17-2010, 01:18 PM

Quote:

Originally Posted by dstorey

The mention that 134A conversions fail. The problem with conversions is that while 134a approximates R12 it is less effecient and a system not designed for it has less margin. The other problem is that 134 uses different oils than r12 and needs different seals. So what everyone does is replace all the o rings with nitrile or something that is compatable with the oil forgetting that there are seals in the compressor. Also all the old oil needs to be flushed out and a new receiver dryer installed

The problems with original R12 systems converted to R134a go MUCH farther than the seals or any other leak issue. Converted systems run higher high side pressures putting more stress on the compressor and all other high side components. Aggravating the problem and contributing to the statistical failure time line is the fact that many conversions do not get the proper attention to lubrication as you describe.

As I said, statistically, converted systems experience problems at the two year mark. This is fact determined from carefully recorded data, not imagination or wild dreams.

davidmash · #12 05-17-2010, 10:38 PM

I use the Mid-cites MP. Ray and Jimmy are the ones who I spoke with at length about the R134 and both suggested it.

The sight glass was bubbly when it was low and with 1.7 lbs of R134 the sight glass is clear now.

I will have to look at my paper work but I think I am on my 3rd or 4th TX summer.