W124, 90psi high side? - PeachParts Mercedes-Benz Forum

Hit Man X · #1 06-13-2006, 04:52 PM

My chum's 300E was converted to 134A before he purchased it (

) anyway, threw the gauges on there and the high side was only 90psi.

NOW since I believe it was converted with one of those cheapo kits, I seriously doubt the o-rings and what not were swapped.

Would a dying compressor cause low high side pressure or is the damned thing just low on 134A?

Thanks for any help.

rickpark · #2 06-13-2006, 05:29 PM

What is the low side pressure?

Is the 90psi the static pressure or pressure during operation.

If it is also low relative to the normal pressure, then you have low refrigerant.

Of course, a compressor that has leaky seals could be the reason you have low refrigerant among other reasons.

Hit Man X · #3 06-14-2006, 12:50 AM

Well crap, I forgot to write it down.

The 90 was under operation.

If I'm low on refer, how should the low side read?

Mike Murrell · #4 06-14-2006, 12:30 PM

If you believe info found in the a/c theory manuals and what you can read at the various WEB yack sites, R-12 high side pressure as a "rule of thumb" is approx. 2.5 times the ambient temp reading taken about a ft. in front of the cars condensor. I realize there are variations in the different systems out there.

If the reading taken is 90F, multiply 90 x 2.5 = 225 lbs.

You did mention R134A and the pressure in that refrigerant is different than R-12, but in your case, I believe this formula has value. It indicates that you are way deficient on the high side.

I would take a static reading of your low side and report that value here so that a knowledgeable person could comment. You take this reading with the car & a/c turned off. Kind of like checking pressure in your tires. I've always believed that a simple static reading is a good place to start, especially if one suspects a low charge condition.

My 2 cents.

Richard Wooldridge · #5 06-14-2006, 01:28 PM

Hi there,
I am wondering if your compressor was even turning - the 90psi means that the ambient temperature was somewhere around 84 degrees. Was that the approximate temperature when you checked the pressure? If it was, the compressor wasn't running. Usually a system charged with R-12 will show around 200 - 240psi on the high side, R-134 system will show 250 - 300psi on the high side. On a properly charged R-12 system the low side is usually regulated at around 34 - 36 psi so the evaporator won't freeze up. On a converted system you will see a higher pressure, around 40 - 45 psi.

Hit Man X · #6 06-15-2006, 06:25 PM

Okay, I'll check it early next week and report back!