Resealing a 30 year old Denso AC compressor

[Kurtatron]

Good Morning,

I had a big leak in my 91 Toyota. I decided to go haywire and replace every single O-ring in the 30 year old AC system. Amazingly, Toyota still had the original Oem R12 o-rings available for cheap.
For the compressor I bought an eBay reseal kit. I watched a YouTube video, how to reseal a Denso 10P compressor. It didn’t seem too difficult.

I have replaced all the seals on the compressor, including shaft seal.

Before putting everything back on the vehicle, is a vacuum test sufficient for a leak test? I don’t want to assemble the entire system again and find out it has a gaping leak.
I did a vacuum test on the compressor, and it did not leak overnight. It stayed right at -19psi for 12 hours.
Is a pressure test absolutely necessary? I studied nitrogen pressure tests, and they did seem more representative of an AC system than a vacuum test.
Anyone experienced with AC?

 

[vwmaniaman]

Did you blow out your hoses and coils with cleaner. New Dryer? You would be amazed at the snot that comes out of a good flushed system.

 

[Racer4]

Did you blow out your hoses and coils with cleaner. New Dryer? You would be amazed at the snot that comes out of a good flushed system.

Being you opened the system you need to replace the dryer as vwmaniaman had stated above. Do not forget the orifice/filter!

 

[NutherDriver]

In general a system that's okay and develops a leak should just have the leak fixed and then be recharged. If things are worse than 'develops a leak' -- compressor failure, system has been discharged or open for a while, you are converting to another refrigerant -- then the bigger job is probably advisable.

1. Take out all the parts including plumbing, flush, with commercial flushing solvent, and blow out with shop air -- little tire pump compressor isn't enough. Exceptions -- DON'T solvent flush/blow out the compressor or evaporator valve. Failed compressor gets replaced, evaporator valve just keep it clean. Do nothing with the filter/dryer -- buy a new one but leave the seal in place until you install it. .

If there's foreign material in the system from a failed compressor, junkyard source, etc. your flushing/blowing out must be fanatical -- unless it's really clean it'll never work. On modern cars the condenser may not be flushable if there is debris in the system -- passages are too small.

The evaporator assembly needs to be taken out, disassembled, thoroughly cleaned. In an old car it might be well to replace it due to dirt, bugs, corrosion that are very hard to clean up. Newer cars have a cabin air filter that should protect from all that.

As each part is flushed and blown out, plug the ends to keep it clean.

2. Reassemble all the parts with new O-rings; oil the rings/joints as you hook up. Add recommended amounts of correct oil for your refrigerant (best with a UV leak detector dye) to each part as you go -- the car manufacturer will tell you what those amounts are. Install the new filter dryer last and close the system up. Reusing the compressor I wouldn't add oil to it -- flush it by hand with clean oil keeping track of any net addition. Hook up a vacuum pump and pull a vacuum for an hour or so. After just a few minute you should get a vacuum that shows as zero absolute pressure (like about -15 psig) on your gauge. Except for possible pump overheating you can't overdo this because you want to boil off all traces of moisture and cleaning solvent as well as remove all air that's dissolved in oil.

Turn off the pump; the system should hold that vacuum. 10 minutes or so holding vacuum is enough. Holding a vacuum is a stiffer test than modest (safe) amounts of pressure. Never run the compressor with a vacuum on the system -- that's likely to kill the compressor.

3. Recharge following the car maker's directions. If in doubt about system tightness (junk parts ...) then put in just a can (or pound) of refrigerant and check for leaks using either a leak tester or UV light source in total darkness. When satisfied finish filling up and test again.

Virtually all the problems I've had taking care of my old cars for a few decades were because of insufficiently clean work. The technology has been so good for so long that genuine parts failures are rare and virtually all from abuse -- collision, cracking a pipe by bending it, etc.