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Originally Posted by jcyuhn
Seems overcharged to me. Both the high and low sides are reading higher than desired. Overcharging also reduces capacity; that would explain the cool but not cold situation. I would pull out refrigerant until the low side shows ~35PSI while running the engine at 2K RPM. Low side pressure is what controls the evaporator temperature.
In my experience Mercedes specs steep high side pressures. Still, 375 is darn high. You're probably close to triggering the high side cutout. While I'm not familiar with the 126 chassis, the 123 & 124 service manuals would state that ~300PSI on the high side is expected under those conditions.
So long as the high side is acceptable after setting the low side to the proper pressure I wouldn't sweat it.  R-134a is going to run higher high side pressures than R-12. My gut feel is that anything below 325PSI under your stated conditions would be OK.
I see we are going to have 98 degree highs later this week; guess you'll get to try it out real soon.
- JimY |
Thanks Jim, I always appreciate the insightful manner in which you post. You have confirmed all my thoughts. In the back of my mind I was thinking 35/300 would be ideal but with these converted systems you can never be positive. You have educated me with regard to the low-side controlling evap temp; I didn't know that. I guess I have always focused on the high side pressures out of concern for the compressor more than anything, and tended to disregard low-side.
Interestingly, I checked out the specs on the
binary switch for my car which shows a high-pressure cutout of 30bar or about 435 psi. It seems to me that such a high pressure might damage the compressor, but if MBZ thinks 435 is OK, then it must be. I will evacuate this evening after work to bring the pressures more in line with 35/300. You're right - the temps around 98 will be a good test! Thanks again.