My car A/C is not cooling. It has R12 fittings on the compressor. I took one of the valve covers off and pushed in the schrader valve and I did get a hissing sound. I bought some Johnsens Freeze 12 and some oil. One of the auto parts stores I sell parts to suggested putting in cheaper r134a and some leak detector to find the leak first before I a)put on a new drier etc. and put in expensive freeze 12 only to have it possibly leak out. Do you all agree with this assessment?

How long ago did the system work? Can you see any wet connections were the oil and freon may have leaked out? If you have not lost the oil, you do not want to overfill the system. Since R134 is cheaper and easier on our enviroment, your approach sounds reasonable. Check my thread on HVAC, it will give a few names of venders that work on the old R12 systems. If the compressor is shot, you may want to convert to R134.

My wifes uncle lives close to me. He had R12 gauges and a vacuum. I was going to put a little dye in there with some 134A and see if a leak was obvious before pumping in the liquid gold known as R12.

How long ago did the system work? Can you see any wet connections were the oil and freon may have leaked out? If you have not lost the oil, you do not want to overfill the system. Since R134 is cheaper and easier on our enviroment, your approach sounds reasonable. Check my thread on HVAC, it will give a few names of venders that work on the old R12 systems. If the compressor is shot, you may want to convert to R134.

R134A isnt compatible with R12. If you do that it may contaminate the system and cause big problems. My experience is in residential appliance repair and I know for certain you cant put 134A in a R12 system in my field at least. Save yourself some money and take it to repair shop.

Brian

You also can't mix Freeze 12 with R12. To go from one to the other, I believe you have to evacuate the system first, but research whether there's anything else you need to do too.

FAIW, we did a cheap 134a conversion on a GM R12 system (changing a few fittings), and it worked pretty badly, ultimately blowing up in an impressive display of spraying freon. I wouldn't recommend it, especially in a place as hot as Houston.

Ben,

It would be quickest and most cost effective to put in just enough R12 and dye in the system to get the compressor to engage, then let it run for a while and check for leaks. If you use the fluorescent detection lamp, the leak will show up real quick. After that just address the leak. FYI - The Hitachi system that Nissan used has a real whack-job of an expansion valve - not replaceable.

A/C service is not work I'm comfortable doing myself, personally. It takes equipement- manifold gauges,vacuum pump, etc. They are often available from auto stores for rent or loan but I pick my battles carefully.

Faced with an inoperative A/C system (77 280) last summer, I elected to have the local Nissan dealer convert from R12 to R134a. The evacuation/recharge was $128 (labor and freon). The conversion kit costs $76 and labor was $84. The icy cold result was really appreciated all last summer.

This past weekend was an opportunity to use the A/C but the chill was gone. A neighbor, whose is a pro HVAC tech, took a look for me and is of the opinion that there is a slow leak in the core valves, indicated by a short "hiss" when he removed the protective caps. He said that in his experience, the Schrader valves are the most common leak point and the most overlooked replacement part during an overhaul/conversion/recharge.

He also noted that the original reciever/drier was still in place. His personal and professional opinion is that the R/D should always be replaced during a conversion and even if the system has been exposed to atmosphere or a low/no pressure condition.

I am going to order a new r/d and valve/cap kit and have the system serviced again. I hope that the dealer will work with me on this, as it appears that perhaps the job was not as comprehensive as it should have been.

If you find a good price on a R/D let me know as the only I have found is from Four Seasons and was around $60 I believe.

A/C service is not work I'm comfortable doing myself, personally. It takes equipement- manifold gauges,vacuum pump, etc. They are often available from auto stores for rent or loan but I pick my battles carefully.

Faced with an inoperative A/C system (77 280) last summer, I elected to have the local Nissan dealer convert from R12 to R134a. The evacuation/recharge was $128 (labor and freon). The conversion kit costs $76 and labor was $84. The icy cold result was really appreciated all last summer.

This past weekend was an opportunity to use the A/C but the chill was gone. A neighbor, whose is a pro HVAC tech, took a look for me and is of the opinion that there is a slow leak in the core valves, indicated by a short "hiss" when he removed the protective caps. He said that in his experience, the Schrader valves are the most common leak point and the most overlooked replacement part during an overhaul/conversion/recharge.

He also noted that the original reciever/drier was still in place. His personal and professional opinion is that the R/D should always be replaced during a conversion and even if the system has been exposed to atmosphere or a low/no pressure condition.

I am going to order a new r/d and valve/cap kit and have the system serviced again. I hope that the dealer will work with me on this, as it appears that perhaps the job was not as comprehensive as it should have been.