Howdy! I have a 79 300SD with an A/C problem. Only the defrost button works on my A/C control panel. If my memory serves me correctly, this is due to a low, or non-existent, charge of freon. I am going to get a hold of someR12 and was wondering what is the proper way in which to chargethe system and how much refrigerant is needed? I look forward to any relpies and I thank you in advance!

 

Well this much I know from my years of refrigerant work and that is if the system is low you have a leak. You need to locate the leak first or you will be right back to square one which is adding more refrigerant. Also the compressor oil needs to be checked if the freon left then the oil probably migrated with it. If the seals in an ac system aren't lubricated regularly then they dry, crack and can even leak. I suggest some r-12 with uv leak detector if you can even get the stuf anymore.
After you find the cause of the leak, I can send you the factory specs on charging the system if your interested. six pages just on checking the ac on your car. Is it the York compressor? I believe there should be a sight glass to see if there is refrigerant in the system. Gas should flow by the sight glass with no bubbles in the line.
Hopes this helps.

 

u should get the r134a conversion kit cuz it may be hard to find [if u do expensive] r12