A/C: How do you tell if R12 or R134a?
 

I bought an '85 MB 300TD with a non-working A/C that I want to fix.

The PO said the car was converted to the new system years ago.

I see no mention of it in the paperwork I received or labeled under the hood.

Is there anyway to verify this car has or has not been converted to R134a?

J.J.

If it has any remaining R134 in the system an A/C shop with a Refridgerant identifier can tell what it is. If it has lost all pressure it needs a proper rebuild and flush so now is a good time to fix it right and use R-12.

The fittings are different for 12 and 134 -134 having the larger fittings.

Here are some PICTURES to help

Assuming they changed the fittings....My W116 has the lable that its converted but has the smaller shrader valves still.

Guess you could be right - made the general assumption the conversion was done at a level of competency - was thinking if it was backyard mech. the 134 cans wouldn't fit the old shrader

if the system is still pressurized with refridgerant, you should be able to tell by checking system pressure (compressor off) R12 and R134a have different pressures depending on temperature. At 70F, it's way too close to call. At 40F or 100F, you should see a difference. But you'll need a refridgerant detector to know if they have been mixed, or god knows what else put in there.

You should never ASSUME anything when it comes to refrigerant conversion.

Federal law requires the correct fittings and a conversion label, but if 50% of the cars that have been converted to 134 have these I would be surprised. I have seen all levels of conversion ranging from, just putting 134 in a system with a suicide hose through the existing fittings, to complete system rebuild with flushing, r/d, big condensor, evacuation, fittings et al.

As mentioned in this thread, the ONLY way to know is with a refrigerant identifier.

Good luck,

Amen to that,

I have done many conversions, and I never use the adapters for the line hoses, because my manifold set is old. I just put the low side adapter in the center of my manifold so that I can get proper pressures instead using the sight glass technique. (I own all of these cars, and never sell them) You definitely don't want to add freon for trouble shooting until you know for sure. On the other hand, if the system is already open, or if you are going to be opening the system, changing the compressor or cores etc, you will need to change the drier, flush, vacuum, reoil, and recharge anyways, so you can make the choice at that time what refigerant to use.