Air Conditioning pressure question?

[mikec]

I have a vintage 1973 Mercedes. Last year the air conditioning was repaired and converted to R134. I was told that because of the age of the system and the hoses, it may be likely that i'll have to charge it with 134 every year. My question is: How do I know how much R134 to add?

I have a guage that goes on the vacuum side, but I forget what the proper reading is, and is it read with the compressor running or not?

Any air conditioning mechanics out there willing to share knowledge?

Thanks

MikeC

 

[tucsonsx]

I'm no expert - but here goes:

134a is more critical of over or under filling than R12; however I have had good luck by filling just until the bubbles disappear from the sight glass ( which going from memory your car has ). Late model stuff without a sight glass has to be evacuated and recharged with a preset amount.

134A is also a smaller molecule than R12 so it will escape from the system more readily than R12; that is why you will probably have to put a small amount in each year. This is especially true with retrofitted systems; however I have found it true of late model systems as well - just to a lesser extent.

Johnson's Freeze 12 seems to work better than 134A in old systems, and there is no retrofitting - you just evacuate the R12 and put it in. Does anyone out there know of a downside to Freeze 12?