R12 to R134

[Mastiff]

I've got all my parts and the R134a with oil in it. The one thing I don't know is how to vacuum down the system at home. I asked at O'Reilly and they don't have anything for rent, and neither does Autozone. Is there a way? How much vacuum do I need to pull? I have a mityvac, but it's a puny little thing.

 

[frankin5]

You need an AC vacuum pump to pull 30" of Mercury and have it hold that for thirty minutes.

 

[Kenny78]

Autozones around here rent them. You might check another autozone to see about different results, sad but usually effective.

You'd have a sore hand using a mity-vac LOL

 

[73k5blazer]

Watch this guys video. It's for a Pontiac 6000, but the procedure is the same. I just did this on my '89 STE and it worked awesome. Replaced dryer, new orings, cleaned everything perfect, new oil, vaccumed condenser, evap, lines all individually for hours then whole system for hours...filled up with duster....blowin' 40 no issues.

There's a 2nd part too. It's lenghty but very detailed. He also replaced the compressor, I didn't do that if you think yours is ok, no need. Use 134a if you don't want to use duster. Although according to GM's own test duster (R152a) was a much better replacment for systems designed for R12.

The mighty vac will work so long as it pulls 30hg. But you'll need to leave it on there for hours, overnight preferably. The key to a good vacuum job is time. It's pulling every little moisture drop. You can't just pull 30hg and turn it off. That'd be all of 30seconds with a real vacuum pump or 2-4 mins with your mighty vac. Leave it run, that's the key, get every contaminant out of the system.

 

[Blue85]

Another option is to pay a shop just for vacuum, as they will have a nice dual stage electric pump. I paid $20 for this once. Of course to do this you need to be confident that there are no leaks. You could use the Harbor Freight venturi pump to get there if you have a decent air compressor (https://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html). It's also useful for some other vacuum jobs, but at this point you're like 1/3rd or 1/3-way to the Harbor Freight single-stage. So maybe it's worth even calling an Autozone in another town. With many loan-a-tool, you can drop off at any store.

 

[Mastiff]

Turns out the oreilly guy was wrong. AutoZone does have the stuff for loan. I'll go that route once I get the right drier. Rock Auto sent something with the ports in the wrong locations, and a weirdly curved tube. I posted another thread venting about their return policy...

 

[Kenny78]

One important thing, make sure your charging hose or gauges make a good connection on the adapters. I had borrowed a manifold gauge for the initial charge but only owned a cheap gauge with a single hose and qd couplers for lo and hi with a screw in can piercer. The low won't snap on the adapter so to charge it you must manually hold it on.... Lots of fun and leaks a little if you don't pay attention.