<** edited to add add'l comments based on the replies...

I believe I'm going to stick with the R12 and just want to clarify what was said: To take this approach I will simply need to flush, replace the filter drier and recharge with R12, right??!!

And the potential issue of the fan not running could be due to a low charge in my system right now vs. malfunction and to verify I need to check the voltage to the fan--but, for a numskull like myself, how do I do that?? I've looked at the fan assembly and cannot see anywhere that I would be able to do that very thing...help!!

Thanks for the replies--I appreciate it!!

end of editing **>

I know there are a lot of threads about these chemicals but think I might have a new and interesting scenario to present (maybe not??). A/C blows really cold while moving once the car is cooled down a bit but if I need to stop at a light after the car has been sitting in the wonderful heat here in AZ then it is almost useless.

Took car (1990 300D, 147K miles) into the shop for this and other check ups early this week and the mechanic told me I've got a mix of 73% R12 & 27% R134 and that he wouldn't be able to recharge unless the system was evacuated (which he couldn't do). Apparently PO did this as I have not done anything with the AC to this point.

Will this cause me any significant problems until I can find someone to evacuate and recharge with R12 (that is what he said should have been in there)?? Also, how much should I expect to pay for this??

He also said my auxiliary fan (driver's side) was not turning on and I'm wondering what troubleshooting can be done (if any) to determine if the fan itself is bad or whether it might be a sensor or something like that?? He wanted to replace to the tune of about $200 (not including some other repairs) and I said to hold off for now.

Thanks for all your help! Mike

To begin with, you need to simply check voltage to the fan with everything turned on. If there is voltage, the fan motor is bad, if there isn't, you need to trace back and find where the problem is. In the case of no voltage, the problem is likely the pushbutton unit.

As for the mix. The problem with this is that the r134 is not compatible with the mineral oil originally used with the R12. To do this right, the system needs to be disassembled at every joint and flushed, the flush COMPLETELY blown out, proper orings installed, the filter drier replaced, the compressor oil drained and replaced with r134 compatible oil, r134 adapter fittings installed, system evacuated and charged.

There is also the alternative of completely flushing the system, replacing the filter drier and going back with R12. If you live in Arizona, you should give this some consideration. It will retain maximum cooling capacity which you need in Arizona. You will lose 15 to 20% by going to r134.

Since it sounds like you are not willing or able to put this kind of money in the system, at a minimum, the system needs to be emptied, ester oil put in the compressor, r134 adapter fittings installed, evacuated and charged with r134.

Good luck,

Scarbrm,

I can't comment on the the mix of the gases, but the original problem of ac not cooling when car is noot moving as due to the non functioning aux fan. I went through this a couple of years ago on a Japanesse car.

Larry has a good point about going back to straight R-12.

Regards

I don't know about the Japanese car referred to, but this is not the case with the 123 or 124 Benz AC's. The auxilliary fan is turned on by a high side pressure switch. Whenever it comes on, it's function is to prevent the high side pressure from becoming excessive. If it is not cooling, stopped at idle, it is likely undercharged.

Have a great day,

I'm not sure thats possible. The fittings for the different types of freon are different. An R12 tank wouldn't fit on a R134 system and vice versa.