Automotive AC troubleshooting 101 - help me get started?

You’re required by law to find the source of the leak.

It’s part of the reason why I sometimes like HC refrigerants as a stopgap in old cars. Makes for an easier check-out. Dyes are also your friend.

Gauges on high and low side are also important. A cheap gauge may show no pressure, but is it really the case? Is that true?

Refill IMO should be done by machine by mass in the end.
 
A can of r134a has about the same global warming potential as the CO2 released from driving 1000 miles
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This isn’t a shade tree v. Professional discussion.

It’s an EPA regulation discussion. In order to legally work on AC systems, and to buy refrigerant in quantity, you have to pass the EPA 609 certification, which stipulates how systems are to be handled, tested, and repaired.

Also, the high side runs closer to 200 PSI, so a 50 PSI test may not reveal the leak.
Yes of course you need to recover the system and not vent refrigerant to the atmosphere.

My "shade tree" comment is just about how to pressurize an empty system without sourcing a bottle of nitrogen. In order to do a soap spray test.

Shade tree - how to do it with what most people have at home.
 
That's acceptable only if you have a way to remove moisture from the air. Like a good filter like a paint shop would have.
I have painted a few cars - way back when. The fairly inexpensive oil/water separators do a pretty good job. Its empty now, so I am going to need to pull a vacuum on it for a long time before refilling anyway, so that should pull any remaining water out.
 
So while I understand the parts of an Automotive AC system quite well, I have no real practical experience because I haven't had many problems. My Xterra AC quite working one day - more or less overnight my daughter tells me ?

Put a cheap refill gauge on it and the system is empty it appears.

Is my first step to pull a vacuum on it and hopefully find / hear something?

Or do I pull a vacuum, fill it with refrigerant and die, and hope I can see it?

Suggestions on a guage set and vacuum pump? Is the Harbor Freight stuff acceptable, or the cheap stuff on Amazon, or should I look elsehwere?
It's a sealed system and you have a leak. Bring it to a Pro.
 
If the Schrader valves are actually leaking, you can confirm this with the system running while spraying soapy water see if it bubbles. I highly doubt it is the case. I am thinking the leak is elsewhere.

According to Rainman Ray, Schrader valve leaks are common. That's also my experience. Last time I had one I put blue nylog on the Schrader valve cap and screwed it back on. So far so good.
 
You’re required by law to find the source of the leak.

It’s part of the reason why I sometimes like HC refrigerants as a stopgap in old cars. Makes for an easier check-out. Dyes are also your friend.

Gauges on high and low side are also important. A cheap gauge may show no pressure, but is it really the case? Is that true?

Refill IMO should be done by machine by mass in the end.
it seems like it’s the local municipality or states that dictate whether a leak needs to be found.
The EPA appears to have no such mandate for vehicles, at least according to this Google AI result.

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it seems like it’s the local municipality or states that dictate whether a leak needs to be found.
The EPA appears to have no such mandate for vehicles, at least according to this Google AI result.

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Why do I care what AI says?

Read section 609 of the Clean Air Act. The law.

Here’s the EPA’s synopsis on venting:

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You can play sea lawyer all you want, but if you know you have a leak, and you refill (i.e. maintain or service) without repairing the leak, you are knowingly venting.
 
Yes. I had to make a special adapter just for this. Highly recommend.
The right approach is nitrogen with R22 blended in. I don’t have that, nor do most. I like to use HC refrigerant as a proxy for leak checking.

Using compressed air unless bone dry introduces more moisture into the system which is not good.
 
According to Rainman Ray, Schrader valve leaks are common. That's also my experience. Last time I had one I put blue nylog on the Schrader valve cap and screwed it back on. So far so good.
You still need to confirm everything. If it's the case then great, what if it's not the case?
 
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