Freon swap

from what i did back in my garage days was to change out the high side/low side charging fittings (usually come in a kit), and drain out the old freon and the compressor oil too as well.

new/fresh oil, and R-134 filled to specs.

we never had to change over anything else, but maybe the receiver/drier (basically a filter)

but too, that being such an old truck, there can be and very well may be seal leaks around the compressor pulley and at many connections, (look for lots of caked on dirt at all these places) so be prepared to do a leak test, with a leak detector, maybe even dye. but you need a full charged system for good results of the testing, so a little to a lot of freon will be wasted.

 

If I remember right: all you "need" is the kit with the new ports for the low and high side to hook up the gauges. Everything else will work but for best efficiency the 134 systems have a larger condenser in front of the radiator.

Edit: what @buddyd157 says

 

I thank the older Petes did OK with the R12 condensers and 134A.
If you can turn the compressor by hand might want to do an extended vacuum. Then see what it does with some freon in it.
I would do a complete flush and dryer as a minimum but you do not even know if your compressor builds pressure.
Search block- top right.

 

when it is pulling a vacuum, it will "level off" on it's own. then you shut off the vacuum, and watch the gauges. an incredibly slow rise will indicate a tiny leak, some wheres in the system.

a sudden sharp rise in the gauges, will indicate a larger leak.

then you'd have to recharge the system, with a dye, run the a/c, you will also need a black light to located the leaks.


and using a "sniffer" have to go to each and every fitting, the compressor, etc, and when the "sniffer" alarms goes off, there's your leak.


you want to do this leak test during calm weather (NO wind), or in a garage, NO running fans..!!

 

The dryer must be changed even if it looks new before the change over to late model freon! If it still has the old stand/up york type A/C comp. buying a adaptor plate and buying a jap. made rotor type a/c comp. will make it blow ice cold.

 

The only real difference is the fittings. You can use a newer compressor, w/o fittings, but will need to change lines to lines with fittings. Or use the old style w/ adapters. The conversion kits had a 4oz. Can of oil. It was either pag or ester oil. Whichever one, it was supposed to be compatible. Bottom line, use correct oil. I’ve been using oil, w/ green dye for a while. Makes finding a leak very easy. Vacuum rule of thumb is 30 lbs, for 30 minutes. In reality 28-29 lbs is all that’s possible, I usually pull one for 45 min- 1 hr. Then let sit for 30 minutes making sure it holds a vacuum. I would check the availablilty of original compressor. If it’s no longer available, might want to upgrade it now, along with new hoses, or adapter manifold with new port fittings.

 

R134a has smaller molecules. It will permeate thru the R12 hoses.

Apparently the R12 condensors don't work as efficiently with R134a either.