If the compressor went south I hope they cleaned the entire system VERY well, as metal particals from the compressor failing could have been sent through your system. It probably worked for a while and then either clogged your system or damaged your new compressor. Need to check pressures and tempratures on your system to give you a better idea of whats exactly going on. But from your description "the aux fan was never coming on with the air running"

This fan has to come on when your compressor is runing for your system to work properly. Your compressor compresses the freon GAS turning it into a high pressure superheated hot GAS, as it goes through your condensor the aux fan cools this GAS and turns the freon into a warm high pressure liquid. You should be able to see this liquid from the site glass on the dryer. This warm LIQUID freon goes through your dryer where your low pressure and hi pressure switches are located. The low pressure switch shuts off the compressor (meaning you have a leak or lost your freon) the Hi pressure switch turns on you aux fan. If your fan is not comming on then you either do not have high enough pressure (225- 300psi depending on outside temp) or your fan switch or wiring is bad. The warm liquid froen goes to the expansion valve where the magic happens. When the warm liquid freon passes thru the small opening it converts back to a gas. (This process is hard to explain and understand as this process absorbs heat and does not produce cold but that is a biproduct of the chemical reaction.) The cold freon gas circulates through your evaporator warm air is blown across the coil and absorbed thus you have cooling and condensation from removing moisture in the air. The longer this chemical reaction takes place then the low side LIQUID freon line starts to sweat, the low liquid freon line starts turning cold with moisture from the expansion valve sometimes all the way back to the dyer. After the freon GAS leaves the evaporator it is sucked by the compressor where you will not have pressure but a vaccum. Then the cycle starts over. Hope this wasn't too long.

If your mechanic is telling you that 134a wont work on your Benz he is wrong. It will it's not as cold but it will work. I would go to a different AC guy and get another opinion. You do have a system failure if your aux fan is not comming on when your compressor is running.


I converted my 260e to 134a and it blows cold. I had several restrictions in the condensor. I had to remove and flush for about an hour to get all the dark brown oil out of the coil. Flushed the evap without removing, flushed all the lines, replaced the dryer, expansion valve and all of the o-rings. I flushed with laquer thinner and shop air in my garage. I also left the condensor out in the sun on my driveway for about an hour so it would heat up and be easier to get the old oil out.

Pulled vacuum for an hour, oil and charged 134a, Blows cold 35 - 40deg out of vents on 99deg. day.

I think 134a works ok and 12 was colder but 134a I can do my self and save a bundle. Only cost me 125.00 parts


Good luck

Anthony