1991 300SL
I've asked about the AC not working and I got a great list of instructions for diagnostics, however some of the instructions didn't work. I did manage to see some codes and some temps (in Celcius) and #1 with a little square. Presumed to mean no codes are stored.....................

Here's the problem... When I start the car the 'EC' is lit, the #3 fan speed is lit, the up arrow is lit, the 'F' has changed to 'C' and the air is coming out of all the vents at full force. I push the automatic button and there is no change in air force but all the other lights go out. Each time I also need to reset 'F'. After a moment the automatic works!
This all doen't happen everytime, just 9 out of 10. I sometimes push off and then auto but the AC still doesn't work (no cool air). This just started this year after winter storage. Could the battery be low?
I just don't know what to look for.
Can you please help me with this?
Thanks in advance,
Marc

A "1" means no codes. I don't think the battery voltage is an issue here, but you can get the controller to display its supply voltage if you want to check it as explained here.

When the A/C is not blowing cold, is the compressor off or on?

[QUOTE]Originally posted by bobterry99
[B]A "1" means no codes. I don't think the battery voltage is an issue here, but you can get the controller to display its supply voltage if you want to check it as explained here.

When the A/C is not blowing cold, is the compressor off or on?
Compressor ON, with no air bubbles visible in sight glass .... Dial @ LO .... rheostat works fine...But, no condenation, ie; water dripping when parked... just plain NO COLD!
Interestingly enough now this problem with the control unit, only after winter storage.

[QUOTE]Originally posted by Marc-1
[B][QUOTE]Originally posted by bobterry99
A "1" means no codes. I don't think the battery voltage is an issue here, but you can get the controller to display its supply voltage if you want to check it as explained here.

When the A/C is not blowing cold, is the compressor off or on?
Compressor ON, with no air bubbles visible in sight glass .... Dial @ LO .... rheostat works fine...But, no condenation, ie; water dripping when parked... just plain NO COLD!
Interestingly enough now this problem with the control unit, only after winter storage.
The voltage is 11 point something which is correct as I know it, but I could be wrong. ;~0
I think I checked that when I did the test. I think now the batt is ok. I now wonder if it's the ignition switch! If only some of the contacts are functional it might cause this problem as well. But then again, would the control unit come on at all???

Your ignition switch is fine. I believe the most likely cause of your problem is a faulty expansion valve. This is diagnosed by measuring the high and low-side pressures of your A/C.

[QUOTE]Originally posted by bobterry99
[B]Your ignition switch is fine. I believe the most likely cause of your problem is a faulty expansion valve. This is diagnosed by measuring the high and low-side pressures of your A/C.
I have a gage... what should the two be reading? Also there are several places to read them. One in the radiator (grill area) one just beside the air cleaner. When I first put the gage on ( beside the air cleaner) it read near 200 psi (Two Hundred), then when I started the car it dropped to 18-20 psi and didn't change. I didn't try the high side yet.
Now for a good question, I've been told that over the winter the O-rings may have shrunk. If the R-12 has leaked out I would like to change to R-134A What is the proceedure for this? Must I change the compressor? Can I just vacuum the system and convert the Shrader valves (inlet, refill valves) with an adaptor then add R-134A??
Even if the expansion valve is faulty this means I need to vacuum the system in order to replace it and replace the refridge with some thing!!! I won't put R-22 in there as it's a propane base refridgerant and ill-advised.
T.I.A

The high pressure fitting is in the grille area, and the low pressure is by the air cleaner. You measured the low side, and I believe the reading should be 29-35. I think the high side is supposed to be 210-257.

There are many opinions on what procedure to follow for converting to R-134. I've read through countless posts on the matter, and I am inclined to think it is best to stay with R-12. And at $20/lb. or so on eBay, it is really not expensive.