i have a 1989 mercedes 190es and i converted the a.c. to 134a the info i have says the low side pressure should be 35-45 psi at 75-85 degrees farenheit but i live in phoenix and the low temp here is more like 85-90 does anybody know what pressure i should have with an ambient temp of 100-105 degrees farenheit ? thanks


Still in the 35-45 range,colder air output at 35psi. There is almost a direct relation between evaporator temp (in F ) and low side pressure in PSI. Air flow across the condensor really affects the high side pressure. Your 35-45 is a good result for a conversion. Remember your outlet temp will be affected by humidity,with monsoon season on us AC systems will suffer. Why not keep a thermometer in your center outlet then you can see what humidity,sun load,fan speed,city driving does to your outlet temp?


I’m not sure about your W201, but I tried a R-134a conversion in one of my W123s and was not satisfied with the results. I converted back to R-12 and was much happier. Hopefully, you car has enough additional cooling capacity to work well with R-134a.


I don’t know just how hot it is when your low side pressure is 75-85 but at 105* and humidity 80%+ the low side is still at about 35psi on a properly operating system. Low side pressure is nearly equal to evaporator surface temperature and 85* isn’t too cool. Without knowing the high side pressure and the circumstances when checked I wouldn’t venture to guess what was wrong, but I feel something certainly is.


RE-read the OP is not saying his low side is 75-85 he is saying that his manual states that he should have a low side pressure of 35-45 when ambient is 75F-85F.The OP never states what pressures he does have,merily what the book says he should have. I agree if your low is 75-85 you have trouble


I miss read that. Excuse me. I was reading and posting while filing an IRS report. I guess I should review that before posting…